The Cluster API project

Cluster API is a Kubernetes sub-project focused on providing declarative APIs and tooling to simplify provisioning, upgrading, and operating multiple Kubernetes clusters.

Started by the Kubernetes Special Interest Group (SIG) Cluster Lifecycle, the Cluster API project uses Kubernetes-style APIs and patterns to automate cluster lifecycle management for platform operators. The supporting infrastructure, like virtual machines, networks, load balancers, and VPCs, as well as the Kubernetes cluster configuration are all defined in the same way that application developers operate deploying and managing their workloads. This enables consistent and repeatable cluster deployments across a wide variety of infrastructure environments.

Getting started

• Quick start
• Concepts
• Developer guide
• Contributing

Using Cluster API v1alpha2? See the legacy documentation.

Why build Cluster API?

Kubernetes is a complex system that relies on several components being configured correctly to have a working cluster. Recognizing this as a potential stumbling block for users, the community focused on simplifying the bootstrapping process. Today, over 100 Kubernetes distributions and installers have been created, each with different default configurations for clusters and supported infrastructure providers. SIG Cluster Lifecycle saw a need for a single tool to address a set of common overlapping installation concerns and started kubeadm.

Kubeadm was designed as a focused tool for bootstrapping a best-practices Kubernetes cluster. The core tenet behind the kubeadm project was to create a tool that other installers can leverage and ultimately alleviate the amount of configuration that an individual installer needed to maintain. Since it began, kubeadm has become the underlying bootstrapping tool for several other applications, including Kubespray, Minikube, kind, etc.

However, while kubeadm and other bootstrap providers reduce installation complexity, they don’t address how to manage a cluster day-to-day or a Kubernetes environment long term. You are still faced with several questions when setting up a production environment, including

• How can I consistently provision machines, load balancers, VPC, etc., across multiple infrastructure providers and locations?
• How can I automate cluster lifecycle management, including things like upgrades and cluster deletion?
• How can I scale these processes to manage any number of clusters?

SIG Cluster Lifecycle began the Cluster API project as a way to address these gaps by building declarative, Kubernetes-style APIs, that automate cluster creation, configuration, and management. Using this model, Cluster API can also be extended to support any infrastructure provider (AWS, Azure, vSphere, etc.) or bootstrap provider (kubeadm is default) you need. See the growing list of available providers.

Goals

• To manage the lifecycle (create, scale, upgrade, destroy) of Kubernetes-conformant clusters using a declarative API.
• To work in different environments, both on-premises and in the cloud.
• To define common operations, provide a default implementation, and provide the ability to swap out implementations for alternative ones.
• To reuse and integrate existing ecosystem components rather than duplicating their functionality (e.g. node-problem-detector, cluster autoscaler, SIG-Multi-cluster).
• To provide a transition path for Kubernetes lifecycle products to adopt Cluster API incrementally. Specifically, existing cluster lifecycle management tools should be able to adopt Cluster API in a staged manner, over the course of multiple releases, or even adopting a subset of Cluster API.

Non-goals

• To add these APIs to Kubernetes core (kubernetes/kubernetes).
  • This API should live in a namespace outside the core and follow the best practices defined by api-reviewers, but is not subject to core-api constraints.
• To manage the lifecycle of infrastructure unrelated to the running of Kubernetes-conformant clusters.
• To force all Kubernetes lifecycle products (kops, kubespray, GKE, AKS, EKS, IKS etc.) to support or use these APIs.
• To manage non-Cluster API provisioned Kubernetes-conformant clusters.
• To manage a single cluster spanning multiple infrastructure providers.
• To configure a machine at any time other than create or upgrade.
• To duplicate functionality that exists or is coming to other tooling, e.g., updating kubelet configuration (c.f. dynamic kubelet configuration), or updating apiserver, controller-manager, scheduler configuration (c.f. component-config effort) after the cluster is deployed.

Community, discussion, contribution, and support

Cluster API is developed in the open, and is constantly being improved by our users, contributors, and maintainers. It is because of you that we are able to automate cluster lifecycle management for the community. Join us!

If you have questions or what to get the latest project news, you can connect with us in the following ways:

• Chat with us on the Kubernetes Slack in the #cluster-api channel
• Subscribe to the SIG Cluster Lifecycle Google Group for access to documents and calendars
• Participate in the conversations on Kubernetes Discuss
• Join our Cluster API working group sessions where we share the latest project news, demos, answer questions, and triage issues
  • Weekly on Wednesdays @ 10:00 PT on Zoom
  • Previous meetings: [ notes | recordings ]

Pull Requests and feedback on issues are very welcome! See the issue tracker if you’re unsure where to start, especially the Good first issue and Help wanted tags, and also feel free to reach out to discuss.

See also our contributor guide and the Kubernetes community page for more details on how to get involved.

Code of conduct

Participation in the Kubernetes community is governed by the Kubernetes Code of Conduct.

Quick Start

In this tutorial we’ll cover the basics of how to use Cluster API to create one or more Kubernetes clusters.

Installation

Common Prerequisites

• Install and setup kubectl in your local environment
• Install Kind and Docker

Install and/or configure a kubernetes cluster

Cluster API requires an existing Kubernetes cluster accessible via kubectl; during the installation process the Kubernetes cluster will be transformed into a management cluster by installing the Cluster API provider components, so it is recommended to keep it separated from any application workload.

It is a common practice to create a temporary, local bootstrap cluster which is then used to provision a target management cluster on the selected infrastructure provider.

Choose one of the options below:

1. Existing Management Cluster

For production use-cases a “real” Kubernetes cluster should be used with appropriate backup and DR policies and procedures in place. The Kubernetes cluster must be at least v1.16+.

export KUBECONFIG=<...>

2. Kind

kind can be used for creating a local Kubernetes cluster for development environments or for the creation of a temporary bootstrap cluster used to provision a target management cluster on the selected infrastructure provider.

The installation procedure depends on the version of kind; if you are planning to user the docker infrastructure provider (CAPD), please follow the additional instructions in the dedicated tab:

kind create cluster

kubectl cluster-info

cat > kind-cluster-with-extramounts.yaml <<EOF
kind: Cluster
apiVersion: kind.x-k8s.io/v1alpha4
nodes:
- role: control-plane
  extraMounts:
    - hostPath: /var/run/docker.sock
      containerPath: /var/run/docker.sock
EOF

export KIND_EXPERIMENTAL_DOCKER_NETWORK=bridge

Install clusterctl

The clusterctl CLI tool handles the lifecycle of a Cluster API management cluster.

curl -L https://github.com/kubernetes-sigs/cluster-api/releases/download/v0.3.24/clusterctl-linux-amd64 -o clusterctl

chmod +x ./clusterctl

sudo mv ./clusterctl /usr/local/bin/clusterctl

clusterctl version

curl -L https://github.com/kubernetes-sigs/cluster-api/releases/download/v0.3.24/clusterctl-darwin-amd64 -o clusterctl

chmod +x ./clusterctl

sudo mv ./clusterctl /usr/local/bin/clusterctl

clusterctl version

Initialize the management cluster

Now that we’ve got clusterctl installed and all the prerequisites in place, let’s transform the Kubernetes cluster into a management cluster by using clusterctl init.

The command accepts as input a list of providers to install; when executed for the first time, clusterctl init automatically adds to the list the cluster-api core provider, and if unspecified, it also adds the kubeadm bootstrap and kubeadm control-plane providers.

Initialization for common providers

Depending on the infrastructure provider you are planning to use, some additional prerequisites should be satisfied before getting started with Cluster API. See below for the expected settings for common providers.

export AWS_REGION=us-east-1 # This is used to help encode your environment variables
export AWS_ACCESS_KEY_ID=<your-access-key>
export AWS_SECRET_ACCESS_KEY=<your-secret-access-key>
export AWS_SESSION_TOKEN=<session-token> # If you are using Multi-Factor Auth.

# The clusterawsadm utility takes the credentials that you set as environment
# variables and uses them to create a CloudFormation stack in your AWS account
# with the correct IAM resources.
clusterawsadm bootstrap iam create-cloudformation-stack

# Create the base64 encoded credentials using clusterawsadm.
# This command uses your environment variables and encodes
# them in a value to be stored in a Kubernetes Secret.
export AWS_B64ENCODED_CREDENTIALS=$(clusterawsadm bootstrap credentials encode-as-profile)

# Finally, initialize the management cluster
clusterctl init --infrastructure aws

export AZURE_SUBSCRIPTION_ID="<SubscriptionId>"

# Create an Azure Service Principal and paste the output here
export AZURE_TENANT_ID="<Tenant>"
export AZURE_CLIENT_ID="<AppId>"
export AZURE_CLIENT_SECRET="<Password>"

# Azure cloud settings
# To use the default public cloud, otherwise set to AzureChinaCloud|AzureGermanCloud|AzureUSGovernmentCloud
export AZURE_ENVIRONMENT="AzurePublicCloud"

export AZURE_SUBSCRIPTION_ID_B64="$(echo -n "$AZURE_SUBSCRIPTION_ID" | base64 | tr -d '\n')"
export AZURE_TENANT_ID_B64="$(echo -n "$AZURE_TENANT_ID" | base64 | tr -d '\n')"
export AZURE_CLIENT_ID_B64="$(echo -n "$AZURE_CLIENT_ID" | base64 | tr -d '\n')"
export AZURE_CLIENT_SECRET_B64="$(echo -n "$AZURE_CLIENT_SECRET" | base64 | tr -d '\n')"

# Finally, initialize the management cluster
clusterctl init --infrastructure azure

clusterctl init --infrastructure docker

# Create the base64 encoded credentials by catting your credentials json.
# This command uses your environment variables and encodes
# them in a value to be stored in a Kubernetes Secret.
export GCP_B64ENCODED_CREDENTIALS=$( cat /path/to/gcp-credentials.json | base64 | tr -d '\n' )

# Finally, initialize the management cluster
clusterctl init --infrastructure gcp

# The username used to access the remote vSphere endpoint
export VSPHERE_USERNAME="vi-admin@vsphere.local"
# The password used to access the remote vSphere endpoint
# You may want to set this in ~/.cluster-api/clusterctl.yaml so your password is not in
# bash history
export VSPHERE_PASSWORD="admin!23"

# Finally, initialize the management cluster
clusterctl init --infrastructure vsphere

# Initialize the management cluster
clusterctl init --infrastructure openstack

export PACKET_API_KEY="34ts3g4s5g45gd45dhdh"

clusterctl init --infrastructure packet

The output of clusterctl init is similar to this:

Fetching providers
Installing cert-manager
Waiting for cert-manager to be available...
Installing Provider="cluster-api" Version="v0.3.0" TargetNamespace="capi-system"
Installing Provider="bootstrap-kubeadm" Version="v0.3.0" TargetNamespace="capi-kubeadm-bootstrap-system"
Installing Provider="control-plane-kubeadm" Version="v0.3.0" TargetNamespace="capi-kubeadm-control-plane-system"
Installing Provider="infrastructure-aws" Version="v0.5.0" TargetNamespace="capa-system"

Your management cluster has been initialized successfully!

You can now create your first workload cluster by running the following:

  clusterctl config cluster [name] --kubernetes-version [version] | kubectl apply -f -

Create your first workload cluster

Once the management cluster is ready, you can create your first workload cluster.

Preparing the workload cluster configuration

The clusterctl config cluster command returns a YAML template for creating a workload cluster.

Required configuration for common providers

Depending on the infrastructure provider you are planning to use, some additional prerequisites should be satisfied before configuring a cluster with Cluster API. Instructions are provided for common providers below.

Otherwise, you can look at the clusterctl config cluster command documentation for details about how to discover the list of variables required by a cluster templates.

export AWS_REGION=us-east-1
export AWS_SSH_KEY_NAME=default
# Select instance types
export AWS_CONTROL_PLANE_MACHINE_TYPE=t3.large
export AWS_NODE_MACHINE_TYPE=t3.large

# Name of the Azure datacenter location. Change this value to your desired location.
export AZURE_LOCATION="centralus" 

# Select VM types.
export AZURE_CONTROL_PLANE_MACHINE_TYPE="Standard_D2s_v3"
export AZURE_NODE_MACHINE_TYPE="Standard_D2s_v3"

# The list of service CIDR, default ["10.128.0.0/12"]
export SERVICE_CIDR=["10.96.0.0/12"]

# The list of pod CIDR, default ["192.168.0.0/16"]
export POD_CIDR=["192.168.0.0/16"]

# The service domain, default "cluster.local"
export SERVICE_DOMAIN="k8s.test"

# The vCenter server IP or FQDN
export VSPHERE_SERVER="10.0.0.1"
# The vSphere datacenter to deploy the management cluster on
export VSPHERE_DATACENTER="SDDC-Datacenter"
# The vSphere datastore to deploy the management cluster on
export VSPHERE_DATASTORE="vsanDatastore"
# The VM network to deploy the management cluster on
export VSPHERE_NETWORK="VM Network"
# The vSphere resource pool for your VMs
export VSPHERE_RESOURCE_POOL="*/Resources"
# The VM folder for your VMs. Set to "" to use the root vSphere folder
export VSPHERE_FOLDER="vm"
# The VM template to use for your VMs
export VSPHERE_TEMPLATE="ubuntu-1804-kube-v1.17.3"
# The VM template to use for the HAProxy load balancer of the management cluster
export VSPHERE_HAPROXY_TEMPLATE="capv-haproxy-v0.6.0-rc.2"
# The public ssh authorized key on all machines
export VSPHERE_SSH_AUTHORIZED_KEY="ssh-rsa AAAAB3N..."

clusterctl init --infrastructure vsphere

clusterctl config cluster --infrastructure openstack --list-variables capi-quickstart

wget https://raw.githubusercontent.com/kubernetes-sigs/cluster-api-provider-openstack/master/templates/env.rc -O /tmp/env.rc
source /tmp/env.rc <path/to/clouds.yaml> <cloud>

# The list of nameservers for OpenStack Subnet being created.
# Set this value when you need create a new network/subnet while the access through DNS is required.
export OPENSTACK_DNS_NAMESERVERS=<dns nameserver>
# FailureDomain is the failure domain the machine will be created in.
export OPENSTACK_FAILURE_DOMAIN=<availability zone name>
# The flavor reference for the flavor for your server instance.
export OPENSTACK_CONTROL_PLANE_MACHINE_FLAVOR=<flavor>
# The flavor reference for the flavor for your server instance.
export OPENSTACK_NODE_MACHINE_FLAVOR=<flavor>
# The name of the image to use for your server instance. If the RootVolume is specified, this will be ignored and use rootVolume directly.
export OPENSTACK_IMAGE_NAME=<image name>
# The SSH key pair name
export OPENSTACK_SSH_KEY_NAME=<ssh key pair name>

# The URL of the kernel to deploy.
export DEPLOY_KERNEL_URL="http://172.22.0.1:6180/images/ironic-python-agent.kernel"
# The URL of the ramdisk to deploy.
export DEPLOY_RAMDISK_URL="http://172.22.0.1:6180/images/ironic-python-agent.initramfs"
# The URL of the Ironic endpoint.
export IRONIC_URL="http://172.22.0.1:6385/v1/"
# The URL of the Ironic inspector endpoint.
export IRONIC_INSPECTOR_URL="http://172.22.0.1:5050/v1/"
# Do not use a dedicated CA certificate for Ironic API. Any value provided in this variable disables additional CA certificate validation.
# To provide a CA certificate, leave this variable unset. If unset, then IRONIC_CA_CERT_B64 must be set.
export IRONIC_NO_CA_CERT=true
# Disables basic authentication for Ironic API. Any value provided in this variable disables authentication.
# To enable authentication, leave this variable unset. If unset, then IRONIC_USERNAME and IRONIC_PASSWORD must be set.
export IRONIC_NO_BASIC_AUTH=true
# Disables basic authentication for Ironic inspector API. Any value provided in this variable disables authentication.
# To enable authentication, leave this variable unset. If unset, then IRONIC_INSPECTOR_USERNAME and IRONIC_INSPECTOR_PASSWORD must be set.
export IRONIC_INSPECTOR_NO_BASIC_AUTH=true

# The project where your cluster will be placed to.
# You have to get out from Packet Portal if you don't have one already.
export PROJECT_ID="5yd4thd-5h35-5hwk-1111-125gjej40930"
# The facility where you want your cluster to be provisioned
export FACILITY="ewr1"
# The operatin system used to provision the device
export NODE_OS="ubuntu_18_04"
# The ssh key name you loaded in Packet Portal
export SSH_KEY="my-ssh"
export POD_CIDR="192.168.0.0/16"
export SERVICE_CIDR="172.26.0.0/16"
export CONTROLPLANE_NODE_TYPE="t1.small"
export WORKER_NODE_TYPE="t1.small"

Generating the cluster configuration

For the purpose of this tutorial, we’ll name our cluster capi-quickstart.

clusterctl config cluster capi-quickstart \
  --kubernetes-version v1.18.19 \
  --control-plane-machine-count=3 \
  --worker-machine-count=3 \
  > capi-quickstart.yaml

clusterctl config cluster capi-quickstart --flavor development \
  --kubernetes-version v1.18.19 \
  --control-plane-machine-count=3 \
  --worker-machine-count=3 \
  > capi-quickstart.yaml

This creates a YAML file named capi-quickstart.yaml with a predefined list of Cluster API objects; Cluster, Machines, Machine Deployments, etc.

The file can be eventually modified using your editor of choice.

See clusterctl config cluster for more details.

Apply the workload cluster

When ready, run the following command to apply the cluster manifest.

kubectl apply -f capi-quickstart.yaml

The output is similar to this:

cluster.cluster.x-k8s.io/capi-quickstart created
awscluster.infrastructure.cluster.x-k8s.io/capi-quickstart created
kubeadmcontrolplane.controlplane.cluster.x-k8s.io/capi-quickstart-control-plane created
awsmachinetemplate.infrastructure.cluster.x-k8s.io/capi-quickstart-control-plane created
machinedeployment.cluster.x-k8s.io/capi-quickstart-md-0 created
awsmachinetemplate.infrastructure.cluster.x-k8s.io/capi-quickstart-md-0 created
kubeadmconfigtemplate.bootstrap.cluster.x-k8s.io/capi-quickstart-md-0 created

Accessing the workload cluster

The cluster will now start provisioning. You can check status with:

kubectl get cluster --all-namespaces

You can also get an “at glance” view of the cluster and its resources by running:

clusterctl describe cluster capi-quickstart

To verify the first control plane is up:

kubectl get kubeadmcontrolplane --all-namespaces

You should see an output is similar to this:

NAME                            INITIALIZED   API SERVER AVAILABLE   VERSION    REPLICAS   READY   UPDATED   UNAVAILABLE
capi-quickstart-control-plane   true                                 v1.18.16   3                  3         3

After the first control plane node is up and running, we can retrieve the workload cluster Kubeconfig:

clusterctl get kubeconfig capi-quickstart > capi-quickstart.kubeconfig

Deploy a CNI solution

Calico is used here as an example.

kubectl --kubeconfig=./capi-quickstart.kubeconfig \
  apply -f https://docs.projectcalico.org/v3.15/manifests/calico.yaml

kubectl --kubeconfig=./capi-quickstart.kubeconfig get nodes

kubectl --kubeconfig=./capi-quickstart.kubeconfig \
  apply -f https://raw.githubusercontent.com/kubernetes-sigs/cluster-api-provider-azure/master/templates/addons/calico.yaml

kubectl --kubeconfig=./capi-quickstart.kubeconfig get nodes

Clean Up

Delete workload cluster.

kubectl delete cluster capi-quickstart

Delete management cluster

kind delete cluster

Next steps

See the clusterctl documentation for more detail about clusterctl supported actions.

Concepts

Management cluster

A Kubernetes cluster that manages the lifecycle of Workload Clusters. A Management Cluster is also where one or more Infrastructure Providers run, and where resources such as Machines are stored.

Workload cluster

A Kubernetes cluster whose lifecycle is managed by a Management Cluster.

Infrastructure provider

A source of computational resources, such as compute and networking. For example, cloud Infrastructure Providers include AWS, Azure, and Google, and bare metal Infrastructure Providers include VMware, MAAS, and metal3.io.

When there is more than one way to obtain resources from the same Infrastructure Provider (such as AWS offering both EC2 and EKS), each way is referred to as a variant.

Bootstrap provider

The Bootstrap Provider is responsible for:

1. Generating the cluster certificates, if not otherwise specified
2. Initializing the control plane, and gating the creation of other nodes until it is complete
3. Joining control plane and worker nodes to the cluster

Control plane

The control plane is a set of services that serve the Kubernetes API and continuously reconcile desired state using control loops.

• Machine-based control planes are the most common type. Dedicated machines are provisioned, running static pods for components such as kube-apiserver, kube-controller-manager and kube-scheduler.

• Pod-based deployments require an external hosting cluster. The control plane components are deployed using standard Deployment and StatefulSet objects and the API is exposed using a Service.

• External control planes are offered and controlled by some system other than Cluster API, such as GKE, AKS, EKS, or IKS.

As of v1alpha2, Machine-Based is the only control plane type that Cluster API supports.

The default provider uses kubeadm to bootstrap the control plane. As of v1alpha3, it exposes the configuration via the KubeadmControlPlane object. The controller, capi-kubeadm-control-plane-controller-manager, can then create Machine and BootstrapConfig objects based on the requested replicas in the KubeadmControlPlane object.

Custom Resource Definitions (CRDs)

Machine

A “Machine” is the declarative spec for an infrastructure component hosting a Kubernetes Node (for example, a VM). If a new Machine object is created, a provider-specific controller will provision and install a new host to register as a new Node matching the Machine spec. If the Machine’s spec is updated, the controller replaces the host with a new one matching the updated spec. If a Machine object is deleted, its underlying infrastructure and corresponding Node will be deleted by the controller.

Common fields such as Kubernetes version are modeled as fields on the Machine’s spec. Any information that is provider-specific is part of the InfrastructureRef and is not portable between different providers.

Machine Immutability (In-place Upgrade vs. Replace)

From the perspective of Cluster API, all Machines are immutable: once they are created, they are never updated (except for labels, annotations and status), only deleted.

For this reason, MachineDeployments are preferable. MachineDeployments handle changes to machines by replacing them, in the same way core Deployments handle changes to Pod specifications.

MachineDeployment

A MachineDeployment provides declarative updates for Machines and MachineSets.

A MachineDeployment works similarly to a core Kubernetes Deployment. A MachineDeployment reconciles changes to a Machine spec by rolling out changes to 2 MachineSets, the old and the newly updated.

MachineSet

A MachineSet’s purpose is to maintain a stable set of Machines running at any given time.

A MachineSet works similarly to a core Kubernetes ReplicaSet. MachineSets are not meant to be used directly, but are the mechanism MachineDeployments use to reconcile desired state.

MachineHealthCheck

A MachineHealthCheck defines the conditions when a Node should be considered unhealthy.

If the Node matches these unhealthy conditions for a given user-configured time, the MachineHealthCheck initiates remediation of the Node. Remediation of Nodes is performed by deleting the corresponding Machine.

MachineHealthChecks will only remediate Nodes if they are owned by a MachineSet. This ensures that the Kubernetes cluster does not lose capacity, since the MachineSet will create a new Machine to replace the failed Machine.

BootstrapData

BootstrapData contains the Machine or Node role-specific initialization data (usually cloud-init) used by the Infrastructure Provider to bootstrap a Machine into a Node.

Personas

This document describes the personas for the Cluster API 1.0 project as driven from use cases.

We are marking a “proposed priority for project at this time” per use case. This is not intended to say that these use cases aren’t awesome or important. They are intended to indicate where we, as a project, have received a great deal of interest, and as a result where we think we should invest right now to get the most users for our project. If interest grows in other areas, they will be elevated. And, since this is an open source project, if you want to drive feature development for a less-prioritized persona, we absolutely encourage you to join us and do that.

Use-case driven personas

Service Provider: Managed Kubernetes

Managed Kubernetes is an offering in which a provider is automating the lifecycle management of Kubernetes clusters, including full control planes that are available to, and used directly by, the customer.

Proposed priority for project at this time: High

There are several projects from several companies that are building out proposed managed Kubernetes offerings (Project Pacific’s Kubernetes Service from VMware, Microsoft Azure, Google Cloud, Red Hat) and they have all expressed a desire to use Cluster API. This looks like a good place to make sure Cluster API works well, and then expand to other use cases.

Feature matrix

Service Provider: Kubernetes-as-a-Service

Examples of a Kubernetes-as-a-Service provider include services such as Red Hat’s hosted OpenShift, AKS, GKE, and EKS. The cloud services manage the control plane, often giving those cloud resources away “for free,” and the customers spin up and down their own worker nodes.

Proposed priority for project at this time: Medium

Existing Kubernetes as a Service providers, e.g. AKS, GKE have indicated interest in replacing their off-tree automation with Cluster API, however since they already had to build their own automation and it is currently “getting the job done,” switching to Cluster API is not a top priority for them, although it is desirable.

Feature matrix

Cluster API Developer

The Cluster API developer is a developer of Cluster API who needs tools and services to make their development experience more productive and pleasant. It’s also important to take a look at the on-boarding experience for new developers to make sure we’re building out a project that other people can more easily submit patches and features to, to encourage inclusivity and welcome new contributors.

Proposed priority for project at this time: Low

We think we’re in a good place right now, and while we welcome contributions to improve the development experience of the project, it should not be the primary product focus of the open source development team to make development better for ourselves.

Feature matrix

Raw API Consumers

Examples of a raw API consumer is a tool like Prow, a customized enterprise platform built on top of Cluster API, or perhaps an advanced “give me a Kubernetes cluster” button exposing some customization that is built using Cluster API.

Proposed priority for project at this time: Low

Feature matrix

Tooling: Provisioners

Examples of this use case, in which a tooling provisioner is using Cluster API to automate behavior, includes tools such as kops and kubicorn.

Proposed priority for project at this time: Low

Maintainers of tools such as kops have indicated interest in using Cluster API, but they have also indicated they do not have much time to take on the work. If this changes, this use case would increase in priority.

Feature matrix

Service Provider: End User/Consumer

This user would be an end user or consumer who is given direct access to Cluster API via their service provider to manage Kubernetes clusters. While there are some commercial projects who plan on doing this (Project Pacific, others), they are doing this as a “super user” feature behind the backdrop of a “Managed Kubernetes” offering.

Proposed priority for project at this time: Low

This is a use case we should keep an eye on to see how people use Cluster API directly, but we think the more relevant use case is people building managed offerings on top at this top.

Feature matrix

Using Custom Certificates

Cluster API expects certificates and keys used for bootstrapping to follow the below convention. CABPK generates new certificates using this convention if they do not already exist.

Each certificate must be stored in a single secret named one of:

Example

apiVersion: v1
kind: Secret
metadata:
  name: cluster1-ca
type: kubernetes.io/tls
data:
  tls.crt: <base 64 encoded PEM>
  tls.key: <base 64 encoded PEM>

Generating a Kubeconfig with your own CA

1. Create a new Certificate Signing Request (CSR) for the system:masters Kubernetes role, or specify any other role under CN.

openssl req  -subj "/CN=system:masters" -new -newkey rsa:2048 -nodes -out admin.csr -keyout admin.key  -out admin.csr

2. Sign the CSR using the [cluster-name]-ca key:

openssl x509 -req -in admin.csr -CA tls.crt -CAkey tls.key -CAcreateserial -out admin.crt -days 5 -sha256

3. Update your kubeconfig with the sign key:

kubectl config set-credentials cluster-admin --client-certificate=admin.crt --client-key=admin.key --embed-certs=true

Upgrading management and workload clusters

Considerations

Supported versions of Kubernetes

If you are upgrading the version of Kubernetes for a cluster managed by Cluster API, check that the running version of Cluster API on the Management Cluster supports the target Kubernetes version.

You may need to upgrade the version of Cluster API in order to support the target Kubernetes version.

In addition, you must always upgrade between Kubernetes minor versions in sequence, e.g. if you need to upgrade from Kubernetes v1.17 to v1.19, you must first upgrade to v1.18.

Images

For kubeadm based clusters, infrastructure providers require a “machine image” containing pre-installed, matching versions of kubeadm and kubelet, ensure that relevant infrastructure machine templates reference the appropriate image for the Kubernetes version.

Upgrading using Cluster API

The high level steps to fully upgrading a cluster are to first upgrade the control plane and then upgrade the worker machines.

Upgrading the control plane machines

How to upgrade the underlying machine image

To upgrade the control plane machines underlying machine images, the MachineTemplate resource referenced by the KubeadmControlPlane must be changed. Since MachineTemplate resources are immutable, the recommended approach is to

1. Copy the existing MachineTemplate.
2. Modify the values that need changing, such as instance type or image ID.
3. Create the new MachineTemplate on the management cluster.
4. Modify the existing KubeadmControlPlane resource to reference the new MachineTemplate resource in the infrastructureRef field.

The next step will trigger a rolling update of the control plane using the new values found in the new MachineTemplate.

How to upgrade the Kubernetes control plane version

To upgrade the Kubernetes control plane version make a modification to the KubeadmControlPlane resource’s Spec.Version field. This will trigger a rolling upgrade of the control plane and, depending on the provider, also upgrade the underlying machine image.

Some infrastructure providers, such as AWS, require that if a specific machine image is specified, it has to match the Kubernetes version specified in the KubeadmControlPlane spec. In order to only trigger a single upgrade, the new MachineTemplate should be created first and then both the Version and InfrastructureTemplate should be modified in a single transaction.

Upgrading machines managed by a MachineDeployment

Upgrades are not limited to just the control plane. This section is not related to Kubeadm control plane specifically, but is the final step in fully upgrading a Cluster API managed cluster.

It is recommended to manage machines with one or more MachineDeployments. MachineDeployments will transparently manage MachineSets and Machines to allow for a seamless scaling experience. A modification to the MachineDeployments spec will begin a rolling update of the machines. Follow these instructions for changing the template for an existing MachineDeployment.

For a more in-depth look at how MachineDeployments manage scaling events, take a look at the MachineDeployment controller documentation and the MachineSet controller documentation.

Upgrading Cluster API components

When to upgrade

In general, it’s recommended to upgrade to the latest version of Cluster API to take advantage of bug fixes, new features and improvements.

Considerations

If moving between different API versions, there may be additional tasks that you need to complete. See below for instructions moving between v1alpha2 and v1alpha3.

Ensure that the version of Cluster API is compatible with the Kubernetes version of the management cluster.

Upgrading to newer versions of 0.3.x

It is recommended to use clusterctl to upgrade between versions of Cluster API 0.3.x.

Upgrading from Cluster API v1alpha2 (0.2.x) to Cluster API v1alpha3 (0.3.x)

We will be using the clusterctl init command to upgrade an existing management cluster from v1alpha2 to v1alpha3.

For detailed information about the changes from v1alpha2 to v1alpha3, please refer to the Cluster API v1alpha2 compared to v1alpha3 section.

Prerequisites

There are a few preliminary steps needed to be able to run clusterctl init on a management cluster with v1alpha2 components installed.

Delete the cabpk-system namespace

Delete the cabpk-system namespace by running:

kubectl delete namespace cabpk-system

Delete the core and infrastructure provider controller-manager deployments

Delete the capi-controller-manager deployment from the capi-system namespace:

kubectl delete deployment capi-controller-manager -n capi-system

Depending on your infrastructure provider, delete the controller-manager deployment.

For example, if you are using the AWS provider, delete the capa-controller-manager deployment from the capa-system namespace:

kubectl delete deployment capa-controller-manager -n capa-system

Optional: Ensure preserveUnknownFields is set to ‘false’ for the infrastructure provider CRDs Spec

This should be the case for all infrastructure providers using conversion webhooks to allow upgrading from v1alpha2 to v1alpha3.

This can verified by running kubectl get crd <crd name>.infrastructure.cluster.x-k8s.io -o yaml for all the infrastructure provider CRDs.

Upgrade Cluster API components using clusterctl

Run clusterctl init with the relevant infrastructure flag. For the AWS provider you would run:

clusterctl init --infrastructure aws

You should now be able to manage your resources using the v1alpha3 version of the Cluster API components.

Adopting existing machines into KubeadmControlPlane management

If your cluster has existing machines labeled with cluster.x-k8s.io/control-plane, you may opt in to management of those machines by creating a new KubeadmControlPlane object and updating the associated Cluster object’s controlPlaneRef like so:

---
apiVersion: "cluster.x-k8s.io/v1alpha3"
kind: Cluster
...
spec:
  controlPlaneRef:
    apiVersion: controlplane.cluster.x-k8s.io/v1alpha3
    kind: KubeadmControlPlane
    name: controlplane
    namespace: default
...

Caveats:

• The KCP controller will refuse to adopt any control plane Machines not bootstrapped with the kubeadm bootstrapper.
• The KCP controller may immediately begin upgrading Machines post-adoption if they’re out of date.
• The KCP controller attempts to behave intelligently when adopting existing Machines, but because the bootstrapping process sets various fields in the KubeadmConfig of a machine it’s not always obvious the original user-supplied KubeadmConfig would have been for that machine. The controller attempts to guess this intent to not replace Machines unnecessarily, so if it guesses wrongly, the consequence is that the KCP controller will effect an “upgrade” to its current config.
• If the cluster’s PKI materials were generated by an initial KubeadmConfig reconcile, they’ll be owned by the KubeadmConfig bound to that machine. The adoption process re-parents these resources to the KCP so they’re not lost during an upgrade, but deleting the KCP post-adoption will destroy those materials.
• The ClusterConfiguration is only partially reconciled with their ConfigMaps the workload cluster, and kubeadm considers the ConfigMap authoritative. Fields which are reconciled include:
  • kubeadmConfigSpec.clusterConfiguration.etcd.local.imageRepository
  • kubeadmConfigSpec.clusterConfiguration.etcd.local.imageTag
  • kubeadmConfigSpec.clusterConfiguration.dns.imageRepository
  • kubeadmConfigSpec.clusterConfiguration.dns.imageTag
  • Further information can be found in issue 2083

Configure a MachineHealthCheck

Prerequisites

Before attempting to configure a MachineHealthCheck, you should have a working management cluster with at least one MachineDeployment or MachineSet deployed.

What is a MachineHealthCheck?

A MachineHealthCheck is a resource within the Cluster API which allows users to define conditions under which Machines within a Cluster should be considered unhealthy. A MachineHealthCheck is defined on a management cluster and scoped to a particular workload cluster.

When defining a MachineHealthCheck, users specify a timeout for each of the conditions that they define to check on the Machine’s Node; if any of these conditions is met for the duration of the timeout, the Machine will be remediated. By default, the action of remediating a Machine should trigger a new Machine to be created to replace the failed one, but providers are allowed to plug in more sophisticated external remediation solutions.

Creating a MachineHealthCheck

Use the following example as a basis for creating a MachineHealthCheck for worker nodes:

apiVersion: cluster.x-k8s.io/v1alpha3
kind: MachineHealthCheck
metadata:
  name: capi-quickstart-node-unhealthy-5m
spec:
  # clusterName is required to associate this MachineHealthCheck with a particular cluster
  clusterName: capi-quickstart
  # (Optional) maxUnhealthy prevents further remediation if the cluster is already partially unhealthy
  maxUnhealthy: 40%
  # (Optional) nodeStartupTimeout determines how long a MachineHealthCheck should wait for
  # a Node to join the cluster, before considering a Machine unhealthy
  nodeStartupTimeout: 10m
  # selector is used to determine which Machines should be health checked
  selector:
    matchLabels:
      nodepool: nodepool-0
  # Conditions to check on Nodes for matched Machines, if any condition is matched for the duration of its timeout, the Machine is considered unhealthy
  unhealthyConditions:
  - type: Ready
    status: Unknown
    timeout: 300s
  - type: Ready
    status: "False"
    timeout: 300s

Use this example as the basis for defining a MachineHealthCheck for control plane nodes managed via the KubeadmControlPlane:

apiVersion: cluster.x-k8s.io/v1alpha3
kind: MachineHealthCheck
metadata:
  name: capi-quickstart-kcp-unhealthy-5m
spec:
  clusterName: capi-quickstart
  maxUnhealthy: 100%
  selector:
    matchLabels:
      cluster.x-k8s.io/control-plane: ""
  unhealthyConditions:
    - type: Ready
      status: Unknown
      timeout: 300s
    - type: Ready
      status: "False"
      timeout: 300s

Remediation Short-Circuiting

To ensure that MachineHealthChecks only remediate Machines when the cluster is healthy, short-circuiting is implemented to prevent further remediation via the maxUnhealthy field within the MachineHealthCheck spec.

If the user defines a value for the maxUnhealthy field (either an absolute number or a percentage of the total Machines checked by this MachineHealthCheck), before remediating any Machines, the MachineHealthCheck will compare the value of maxUnhealthy with the number of Machines it has determined to be unhealthy. If the number of unhealthy Machines exceeds the limit set by maxUnhealthy, remediation will not be performed.

With an Absolute Value

If maxUnhealthy is set to 2:

• If 2 or fewer nodes are unhealthy, remediation will be performed
• If 3 or more nodes are unhealthy, remediation will not be performed

These values are independent of how many Machines are being checked by the MachineHealthCheck.

With Percentages

If maxUnhealthy is set to 40% and there are 25 Machines being checked:

• If 10 or fewer nodes are unhealthy, remediation will be performed
• If 11 or more nodes are unhealthy, remediation will not be performed

If maxUnhealthy is set to 40% and there are 6 Machines being checked:

• If 2 or fewer nodes are unhealthy, remediation will be performed
• If 3 or more nodes are unhealthy, remediation will not be performed

Note, when the percentage is not a whole number, the allowed number is rounded down.

Skipping Remediation

There are scenarios where remediation for a machine may be undesirable (eg. during cluster migration using clustrctl move). For such cases, MachineHealthCheck provides 2 mechanisms to skip machines for remediation.

Implicit skipping when the resource is paused (using cluster.x-k8s.io/paused annotation):

• When a cluster is paused, none of the machines in that cluster are considered for remediation.
• When a machine is paused, only that machine is not considered for remediation.
• A cluster or a machine is usually paused automatically by Cluster API when it detects a migration.

Explicit skipping using cluster.x-k8s.io/skip-remediation annotation:

• Users can also skip any machine for remediation by setting the cluster.x-k8s.io/skip-remediation for that machine.

Limitations and Caveats of a MachineHealthCheck

Before deploying a MachineHealthCheck, please familiarise yourself with the following limitations and caveats:

• Only Machines owned by a MachineSet or a KubeadmControlPlane can be remediated by a MachineHealthCheck (since a MachineDeployment uses a MachineSet, then this includes Machines that are part of a MachineDeployment)
• Machines managed by a KubeadmControlPlane are remediated according to the delete-and-recreate guidelines described in the KubeadmControlPlane proposal
• If the Node for a Machine is removed from the cluster, a MachineHealthCheck will consider this Machine unhealthy and remediate it immediately
• If no Node joins the cluster for a Machine after the NodeStartupTimeout, the Machine will be remediated
• If a Machine fails for any reason (if the FailureReason is set), the Machine will be remediated immediately

Kubeadm control plane

Using the Kubeadm control plane type to manage a control plane provides several ways to upgrade control plane machines.

Kubeconfig management

KCP will generate and manage the admin Kubeconfig for clusters. The client certificate for the admin user is created with a valid lifespan of a year, and will be automatically regenerated when the cluster is reconciled and has less than 6 months of validity remaining.

Upgrades

See the section on upgrading clusters.

Using Kubeadm Control Plane when upgrading from Cluster API v1alpha2 (0.2.x)

See the section on Adopting existing machines into KubeadmControlPlane management

Running workloads on control plane machines

We don’t suggest running workloads on control planes, and highly encourage avoiding it unless absolutely necessary.

However, in the case the user wants to run non-control plane workloads on control plane machines they are ultimately responsible for ensuring the proper functioning of those workloads, given that KCP is not aware of the specific requirements for each type of workload (e.g. preserving quorum, shutdown procedures etc.).

In order to do so, the user could leverage on the same assumption that applies to all the Cluster API Machines:

• The Kubernetes node hosted on the Machine will be cordoned & drained before removal (with well known exceptions like full Cluster deletion).
• The Machine will respect PreDrainDeleteHook and PreTerminateDeleteHook. see the Machine Deletion Phase Hooks proposal for additional details.

Changing Infrastructure Machine Templates

Several different components of Cluster API leverage infrastructure machine templates, including KubeadmControlPlane, MachineDeployment, and MachineSet. These MachineTemplate resources should be immutable, unless the infrastructure provider documentation indicates otherwise for certain fields (see below for more details).

The correct process for modifying an infrastructure machine template is as follows:

1. Duplicate an existing template. Users can use kubectl get <MachineTemplateType> <name> -o yaml > file.yaml to retrieve a template configuration from a running cluster to serve as a starting point.
2. Update the desired fields. Fields that might need to be modified could include the SSH key, the AWS instance type, or the Azure VM size. Refer to the provider-specific documentation for more details on the specific fields that each provider requires or accepts.
3. Give the newly-modified template a new name by modifying the metadata.name field (or by using metadata.generateName).
4. Create the new infrastructure machine template on the API server using kubectl. (If the template was initially created using the command in step 1, be sure to clear out any extraneous metadata, including the resourceVersion field, before trying to send it to the API server.)

Once the new infrastructure machine template has been persisted, users may modify the object that was referencing the infrastructure machine template. For example, to modify the infrastructure machine template for the KubeadmControlPlane object, users would modify the spec.infrastructureTemplate.name field. For a MachineDeployment or MachineSet, users would need to modify the spec.template.spec.infrastructureRef.name field. In all cases, the name field should be updated to point to the newly-modified infrastructure machine template. This will trigger a rolling update. (This same process is described in the documentation for upgrading the underlying machine image for KubeadmControlPlane in the “How to upgrade the underlying machine image” section.)

Some infrastructure providers may, at their discretion, choose to support in-place modifications of certain infrastructure machine template fields. This may be useful if an infrastructure provider is able to make changes to running instances/machines, such as updating allocated memory or CPU capacity. In such cases, however, Cluster API will not trigger a rolling update.

Experimental Features

Cluster API now ships with a new experimental package that lives under exp/ directory which has new features. This is a temporary location for features which will be moved to their permanent locations after graduation. Users can experiment with these features by enabling them using feature gates.

Enabling Experimental Features for Management Clusters Started with clusterctl

Users can enable/disable features by setting OS environment variables before running clusterctl init, e.g.:

export EXP_CLUSTER_RESOURCE_SET=true

clusterctl init --infrastructure vsphere

As an alternative to environment variables, it is also possible to set variables in the clusterctl config file located at $HOME/.cluster-api/clusterctl.yaml, e.g.:

# Values for environment variable substitution
EXP_CLUSTER_RESOURCE_SET: "true"

In case a variable is defined both in the config file and as an OS environment variable, the latter takes precedence. For more information on how to set variables for clusterctl, see clusterctl Configuration File

Some features like MachinePools may require infrastructure providers to implement a separate CRD that handles infrastructure side of the feature too. For such a feature to work, infrastructure providers should also enable their controllers as well if it is also implemented as features; if it is not implemented as features, no additional step is necessary. As an example, Cluster API Provider Azure (CAPZ) has support for MachinePool through the infrastructure type AzureMachinePool.

Enabling Experimental Features for e2e Tests

One way is to set experimental variables on the clusterctl config file. For CAPI, these configs are under ./test/e2e/config/... such as docker-ci.yaml:

variables:
  EXP_CLUSTER_RESOURCE_SET: "true"
  EXP_MACHINE_POOL: "true"

Another way is to set them as environmental variables before running e2e tests.

Enabling Experimental Features on Tilt

On development environments started with Tilt, features can be enabled by setting the feature variables in kustomize_substitutions, e.g.:

{
  "enable_providers": ["kubeadm-bootstrap","kubeadm-control-plane"],
  "allowed_contexts": ["kind-kind"],
  "default_registry": "gcr.io/cluster-api-provider",
  "provider_repos": [],
  "kustomize_substitutions": {
    "EXP_CLUSTER_RESOURCE_SET": "true",
    "EXP_MACHINE_POOL": "true"
  }
}

For more details on setting up a development environment with tilt, see Developing Cluster API with Tilt

Enabling Experimental Features on Existing Management Clusters

To enable/disable features on existing management clusters, users can modify CAPI controller manager deployment which will restart all controllers with requested features.

#  kubectl edit -n capi-system deployment.apps/capi-controller-manager
   // Enable/disable available feautures by modifying Args below. 
    Args:
      --metrics-addr=127.0.0.1:8080
      --enable-leader-election
      --feature-gates=MachinePool=true,ClusterResourceSet=true

Similarly, to validate if a particular feature is enabled, see cluster-api-provider deployment arguments by:

# kubectl describe -n capi-system deployment.apps/capi-controller-manager

Active Experimental Features

• MachinePools
• ClusterResourceSet

Warning: Experimental features are unreliable, i.e., some may one day be promoted to the main repository, or they may be modified arbitrarily or even disappear altogether. In short, they are not subject to any compatibility or deprecation promise.

Experimental Feature: MachinePool (alpha)

MachinePool feature provides a way to manage a set of machines by defining a common configuration, number of desired machine replicas etc. similar to MachineDeployment, except MachineSet controllers are responsible for the lifecycle management of the machines for MachineDeployment, whereas in MachinePools, each infrastructure provider has a specific solution for orchestrating these Machines.

Feature gate name: MachinePool

Variable name to enable/disable the feature gate: EXP_MACHINE_POOL

Infrastructure providers can support this feature by implementing their specific MachinePool such as AzureMachinePool.

More details on MachinePool can be found at: MachinePool CAEP

Experimental Feature: ClusterResourceSet (alpha)

ClusterResourceSet feature is introduced to provide a way to automatically apply a set of resources (such as CNI/CSI) defined by users to matching newly-created/existing clusters.

Feature gate name: ClusterResourceSet

Variable name to enable/disable the feature gate: EXP_CLUSTER_RESOURCE_SET

More details on ClusterResourceSet and an example to test it can be found at: ClusterResourceSet CAEP

Overview of clusterctl

The clusterctl CLI tool handles the lifecycle of a Cluster API management cluster.

The clusterctl command line interface is specifically designed for providing a simple “day 1 experience” and a quick start with Cluster API; it automates fetching the YAML files defining provider components and installing them.

Additionally it encodes a set of best practices in managing providers, that helps the user in avoiding mis-configurations or in managing day 2 operations such as upgrades.

• use clusterctl init to install Cluster API providers

• use clusterctl upgrade to upgrade Cluster API providers

• use clusterctl delete to delete Cluster API providers

• use clusterctl config cluster to spec out workload clusters

• use clusterctl generate yaml to process yaml

• use clusterctl get kubeconfig to get the kubeconfig of an existing workload cluster. using clusterctl’s internal yaml processor.

• use clusterctl move to migrate objects defining a workload clusters (e.g. Cluster, Machines) from a management cluster to another management cluster

clusterctl Commands

• clusterctl init
• clusterctl config cluster
• clusterctl generate yaml
• clusterctl get kubeconfig
• clusterctl describe cluster
• clusterctl move
• clusterctl upgrade
• clusterctl delete
• clusterctl completion

clusterctl init

The clusterctl init command installs the Cluster API components and transforms the Kubernetes cluster into a management cluster.

This document provides more detail on how clusterctl init works and on the supported options for customizing your management cluster.

Defining the management cluster

The clusterctl init command accepts in input a list of providers to install.

Automatically installed providers

The clusterctl init command automatically adds the cluster-api core provider, the kubeadm bootstrap provider, and the kubeadm control-plane provider to the list of providers to install. This allows users to use a concise command syntax for initializing a management cluster. For example, to get a fully operational management cluster with the aws infrastructure provider, the cluster-api core provider, the kubeadm bootstrap, and the kubeadm control-plane provider, use the command:

clusterctl init --infrastructure aws

Provider version

The clusterctl init command by default installs the latest version available for each selected provider.

Target namespace

The clusterctl init command by default installs each provider in the default target namespace defined by each provider, e.g. capi-system for the Cluster API core provider.

See the provider documentation for more details.

Watching namespace

The clusterctl init command by default installs each provider configured for watching objects in all namespaces.

Multi-tenancy

Multi-tenancy for Cluster API means a management cluster where multiple instances of the same provider are installed.

The user can achieve multi-tenancy configurations with clusterctl by a combination of:

• Multiple calls to clusterctl init;
• Usage of the --target-namespace flag;
• Usage of the --watching-namespace flag;

The clusterctl command officially supports the following multi-tenancy configurations:

Provider repositories

To access provider specific information, such as the components YAML to be used for installing a provider, clusterctl init accesses the provider repositories, that are well-known places where the release assets for a provider are published.

See clusterctl configuration for more info about provider repository configurations.

Variable substitution

Providers can use variables in the components YAML published in the provider’s repository.

During clusterctl init, those variables are replaced with environment variables or with variables read from the clusterctl configuration.

Additional information

When installing a provider, the clusterctl init command executes a set of steps to simplify the lifecycle management of the provider’s components.

• All the provider’s components are labeled, so they can be easily identified in subsequent moments of the provider’s lifecycle, e.g. upgrades.

labels:
- clusterctl.cluster.x-k8s.io: ""
- cluster.x-k8s.io/provider: "<provider-name>"

• An additional Provider object is created in the target namespace where the provider is installed. This object keeps track of the provider version, the watching namespace, and other useful information for the inventory of the providers currently installed in the management cluster.

clusterctl config cluster

The clusterctl config cluster command returns a YAML template for creating a workload cluster.

For example

clusterctl config cluster my-cluster --kubernetes-version v1.16.3 --control-plane-machine-count=3 --worker-machine-count=3 > my-cluster.yaml

Creates a YAML file named my-cluster.yaml with a predefined list of Cluster API objects; Cluster, Machines, Machine Deployments, etc. to be deployed in the current namespace (in case, use the --target-namespace flag to specify a different target namespace).

Then, the file can be modified using your editor of choice; when ready, run the following command to apply the cluster manifest.

kubectl apply -f my-cluster.yaml

Selecting the infrastructure provider to use

The clusterctl config cluster command uses smart defaults in order to simplify the user experience; in the example above, it detects that there is only an aws infrastructure provider in the current management cluster and so it automatically selects a cluster template from the aws provider’s repository.

In case there is more than one infrastructure provider, the following syntax can be used to select which infrastructure provider to use for the workload cluster:

clusterctl config cluster my-cluster --kubernetes-version v1.16.3 \
    --infrastructure:aws > my-cluster.yaml

or

clusterctl config cluster my-cluster --kubernetes-version v1.16.3 \
    --infrastructure:aws:v0.4.1 > my-cluster.yaml

Flavors

The infrastructure provider authors can provide different type of cluster templates, or flavors; use the --flavor flag to specify which flavor to use; e.g.

clusterctl config cluster my-cluster --kubernetes-version v1.16.3 \
    --flavor high-availability > my-cluster.yaml

Please refer to the providers documentation for more info about available flavors.

Alternative source for cluster templates

clusterctl uses the provider’s repository as a primary source for cluster templates; the following alternative sources for cluster templates can be used as well:

ConfigMaps

Use the --from-config-map flag to read cluster templates stored in a Kubernetes ConfigMap; e.g.

clusterctl config cluster my-cluster --kubernetes-version v1.16.3 \
    --from-config-map my-templates > my-cluster.yaml

Also following flags are available --from-config-map-namespace (defaults to current namespace) and --from-config-map-key (defaults to template).

GitHub or local file system folder

Use the --from flag to read cluster templates stored in a GitHub repository or in a local file system folder; e.g.

clusterctl config cluster my-cluster --kubernetes-version v1.16.3 \
   --from https://github.com/my-org/my-repository/blob/master/my-template.yaml > my-cluster.yaml

or

clusterctl config cluster my-cluster --kubernetes-version v1.16.3 \
   --from ~/my-template.yaml > my-cluster.yaml

Variables

If the selected cluster template expects some environment variables, user should ensure those variables are set in advance.

e.g. if the AWS_CREDENTIALS variable is expected for a cluster template targeting the aws infrastructure, you should ensure the corresponding environment variable to be set before executing clusterctl config cluster.

Please refer to the providers documentation for more info about the required variables or use the clusterctl config cluster --list-variables flag to get a list of variables names required by a cluster template.

The clusterctl configuration file can be used as alternative to environment variables.

clusterctl generate yaml

The clusterctl generate yaml command processes yaml using clusterct’s yaml processor.

The intent of this command is to allow users who may have specific templates to leverage clusterctl’s yaml processor for variable substitution. For example, this command can be leveraged in local and CI scripts or for development purposes.

clusterctl ships with a simple yaml processor that performs variable substitution that takes into account of default values. Under the hood, clusterctl’s yaml processor uses drone/envsubst to replace variables and uses the defaults if necessary.

Variable values are either sourced from the clusterctl config file or from environment variables.

Current usage of the command is as follows:

# Generates a configuration file with variable values using a template from a
# specific URL.
clusterctl generate yaml --from https://github.com/foo-org/foo-repository/blob/master/cluster-template.yaml

# Generates a configuration file with variable values using
# a template stored locally.
clusterctl generate yaml  --from ~/workspace/cluster-template.yaml

# Prints list of variables used in the local template
clusterctl generate yaml --from ~/workspace/cluster-template.yaml --list-variables

# Prints list of variables from template passed in via stdin
cat ~/workspace/cluster-template.yaml | clusterctl generate yaml --from - --list-variables

# Default behavior for this sub-command is to read from stdin.
# Generate configuration from stdin
cat ~/workspace/cluster-template.yaml | clusterctl generate yaml

clusterctl get kubeconfig

This command prints the kubeconfig of an existing workload cluster into stdout. This functionality is available in clusterctl v0.3.9 or newer.

Examples

Get the kubeconfig of a workload cluster named foo.

clusterctl get kubeconfig foo

Get the kubeconfig of a workload cluster named foo in the namespace bar

clusterctl get kubeconfig foo --namespace bar

Get the kubeconfig of a workload cluster named foo using a specific context bar

clusterctl get kubeconfig foo --kubeconfig-context bar

clusterctl describe cluster

The clusterctl describe cluster command provides an “at glance” view of a Cluster API cluster designed to help the user in quickly understanding if there are problems and where.

For example clusterctl describe cluster capi-quickstart will provide an output similar to:

The “at glance” view is based on the idea that clusterctl should avoid to overload the user with information, but instead surface problems, if any.

In practice, if you look at the ControlPlane node, you might notice that the underlying machines are grouped together, because all of them have the same state (Ready equal to True), so it is not necessary to repeat the same information three times.

If this is not the case, and machines have different states, the visualization is going to use different lines:

You might also notice that the visualization does not represent the infrastructure machine or the bootstrap object linked to a machine, unless their state differs from the machine’s state.

Customizing the visualization

By default the visualization generated by clusterctl describe cluster hides details for the sake of simplicity and shortness. However, if required, the user can ask for showing all the detail:

By using the --disable-grouping flag, the user can force the visualization to show all the machines on separated lines, no matter if they have the same state or not:

By using the --disable-no-echo flag, the user can force the visualization to show infrastructure machines and bootstrap objects linked to machines, no matter if they have the same state or not:

It is also possible to force the visualization to show all the conditions for an object (instead of showing only the ready condition). e.g. with --show-conditions KubeadmControlPlane you get:

Please note that this option is flexible, and you can pass a comma separated list of kind or kind/name for which the command should show all the object’s conditions (use ‘all’ to show conditions for everything).

clusterctl move

The clusterctl move command allows to move the Cluster API objects defining workload clusters, like e.g. Cluster, Machines, MachineDeployments, etc. from one management cluster to another management cluster.

You can use:

clusterctl move --to-kubeconfig="path-to-target-kubeconfig.yaml"

To move the Cluster API objects existing in the current namespace of the source management cluster; in case if you want to move the Cluster API objects defined in another namespace, you can use the --namespace flag.

Pivot

Pivoting is a process for moving the provider components and declared Cluster API resources from a source management cluster to a target management cluster.

This can now be achieved with the following procedure:

1. Use clusterctl init to install the provider components into the target management cluster
2. Use clusterctl move to move the cluster-api resources from a Source Management cluster to a Target Management cluster

Bootstrap & Pivot

The pivot process can be bounded with the creation of a temporary bootstrap cluster used to provision a target Management cluster.

This can now be achieved with the following procedure:

1. Create a temporary bootstrap cluster, e.g. using Kind or Minikube
2. Use clusterctl init to install the provider components
3. Use clusterctl config cluster ... | kubectl apply -f - to provision a target management cluster
4. Wait for the target management cluster to be up and running
5. Get the kubeconfig for the new target management cluster
6. Use clusterctl init with the new cluster’s kubeconfig to install the provider components
7. Use clusterctl move to move the Cluster API resources from the bootstrap cluster to the target management cluster
8. Delete the bootstrap cluster

Note: It’s required to have at least one worker node to schedule Cluster API workloads (i.e. controllers). A cluster with a single control plane node won’t be sufficient due to the NoSchedule taint. If a worker node isn’t available, clusterctl init will timeout.

Dry run

With --dry-run option you can dry-run the move action by only printing logs without taking any actual actions. Use log level verbosity -v to see different levels of information.

clusterctl upgrade

The clusterctl upgrade command can be used to upgrade the version of the Cluster API providers (CRDs, controllers) installed into a management cluster.

Background info: management groups

The upgrade procedure is designed to ensure all the providers in a management group use the same API Version of Cluster API (contract), e.g. the v1alpha 3 Cluster API contract.

A management group is a group of providers composed by a CoreProvider and a set of Bootstrap/ControlPlane/Infrastructure providers watching objects in the same namespace.

Usually, in a management cluster there is only a management group, but in case of n-core multi tenancy there can be more than one.

upgrade plan

The clusterctl upgrade plan command can be used to identify possible targets for upgrades.

clusterctl upgrade plan

Produces an output similar to this:

Checking new release availability...

Management group: capi-system/cluster-api, latest release available for the v1alpha3 API Version of Cluster API (contract):

NAME                NAMESPACE                          TYPE                     CURRENT VERSION   TARGET VERSION
cluster-api         capi-system                        CoreProvider             v0.3.0            v0.3.1
kubeadm             capi-kubeadm-bootstrap-system      BootstrapProvider        v0.3.0            v0.3.1
kubeadm             capi-kubeadm-control-plane-system  ControlPlaneProvider     v0.3.0            v0.3.1
docker              capd-system                        InfrastructureProvider   v0.3.0            v0.3.1


You can now apply the upgrade by executing the following command:

   clusterctl upgrade apply --management-group capi-system/cluster-api  --contract v1alpha3

The output contains the latest release available for each management group in the cluster/for each API Version of Cluster API (contract) available at the moment.

upgrade apply

After choosing the desired option for the upgrade, you can run the following command to upgrade all the providers in the management group. This upgrades all the providers to the latest stable releases.

clusterctl upgrade apply \
  --management-group capi-system/cluster-api  \
  --contract v1alpha3

The upgrade process is composed by three steps:

• Check the cert-manager version, and if necessary, upgrade it.
• Delete the current version of the provider components, while preserving the namespace where the provider components are hosted and the provider’s CRDs.
• Install the new version of the provider components.

Please note that clusterctl does not upgrade Cluster API objects (Clusters, MachineDeployments, Machine etc.); upgrading such objects are the responsibility of the provider’s controllers.

Upgrading a Multi-tenancy management cluster

Multi-tenancy for Cluster API means a management cluster where multiple instances of the same provider are installed, and this is achieved by multiple calls to clusterctl init, and in most cases, each one with different environment variables for customizing the provider instances.

In order to upgrade a multi-tenancy management cluster, and preserve the instance specific settings, you should do the same during upgrades and execute multiple calls to clusterctl upgrade apply, each one with different environment variables.

For instance, in case of a management cluster with n>1 instances of an infrastructure provider, and only one instance of Cluster API core provider, bootstrap provider and control plane provider, you should:

Run once clusterctl upgrade apply for the core provider, the bootstrap provider and the control plane provider; this can be achieved by using the --core, --bootstrap and --control-plane flags followed by the upgrade target for each one of those providers, e.g.

clusterctl upgrade apply --management-group capi-system/cluster-api \
    --core capi-system/cluster-api:v0.3.1 \
    --bootstrap capi-kubeadm-bootstrap-system/kubeadm:v0.3.1 \
    --control-plane capi-kubeadm-control-plane-system/kubeadm:v0.3.1

Run clusterctl upgrade apply for each infrastructure provider instance, using the --infrastructure flag, taking care to provide different environment variables for each call (as in the initial setup), e.g.

Set the environment variables for instance 1 and then run:

clusterctl upgrade apply --management-group capi-system/cluster-api \
    --infrastructure instance1/docker:v0.3.1

Afterwards, set the environment variables for instance 2 and then run:

clusterctl upgrade apply --management-group capi-system/cluster-api \
    --infrastructure instance2/docker:v0.3.1

etc.

clusterctl delete

The clusterctl delete command deletes the provider components from the management cluster.

The operation is designed to prevent accidental deletion of user created objects. For example:

clusterctl delete --infrastructure aws

Deletes the AWS infrastructure provider components, while preserving the namespace where the provider components are hosted and the provider’s CRDs.

If you want to delete all the providers in a single operation , you can use the --all flag.

clusterctl delete --all

clusterctl completion

The clusterctl completion command outputs shell completion code for the specified shell (bash or zsh). The shell code must be evaluated to provide interactive completion of clusterctl commands. This can be done by sourcing it from the ~/.bash_profile.

Bash

To install it on macOS use Homebrew:

$ brew install bash-completion

Once installed, bash_completion must be evaluated. This can be done by adding the following line to the ~/.bash_profile.

[[ -r "$(brew --prefix)/etc/profile.d/bash_completion.sh" ]] && . "$(brew --prefix)/etc/profile.d/bash_completion.sh"

If bash-completion is not installed on Linux, please install the ‘bash-completion’ package via your distribution’s package manager.

You now have to ensure that the clusterctl completion script gets sourced in all your shell sessions. There are multiple ways to achieve this:

• Source the completion script in your ~/.bash_profile file:

  source <(clusterctl completion bash)
  

• Add the completion script to the /usr/local/etc/bash_completion.d directory:

  clusterctl completion bash >/usr/local/etc/bash_completion.d/clusterctl
  

Zsh

The clusterctl completion script for Zsh can be generated with the command clusterctl completion zsh. Sourcing the completion script in your shell enables clusterctl autocompletion.

To do so in all your shell sessions, add the following to your ~/.zshrc file:

source <(clusterctl completion zsh)

After reloading your shell, clusterctl autocompletion should be working.

If you get an error like complete:13: command not found: compdef, then add the following to the beginning of your ~/.zshrc file:

autoload -Uz compinit
compinit

clusterctl Configuration File

The clusterctl config file is located at $HOME/.cluster-api/clusterctl.yaml and it can be used to:

• Customize the list of providers and provider repositories.
• Provide configuration values to be used for variable substitution when installing providers or creating clusters.
• Define image overrides for air-gapped environments.

Provider repositories

The clusterctl CLI is designed to work with providers implementing the clusterctl Provider Contract.

Each provider is expected to define a provider repository, a well-known place where release assets are published.

By default, clusterctl ships with providers sponsored by SIG Cluster Lifecycle. Use clusterctl config repositories to get a list of supported providers and their repository configuration.

Users can customize the list of available providers using the clusterctl configuration file, as shown in the following example:

providers:
  # add a custom provider
  - name: "my-infra-provider"
    url: "https://github.com/myorg/myrepo/releases/latest/infrastructure_components.yaml"
    type: "InfrastructureProvider"
  # override a pre-defined provider
  - name: "cluster-api"
    url: "https://github.com/myorg/myforkofclusterapi/releases/latest/core_components.yaml"
    type: "CoreProvider"

See provider contract for instructions about how to set up a provider repository.

Variables

When installing a provider clusterctl reads a YAML file that is published in the provider repository; while executing this operation, clusterctl can substitute certain variables with the ones provided by the user.

The same mechanism also applies when clusterctl reads the cluster templates YAML published in the repository, e.g. when injecting the Kubernetes version to use, or the number of worker machines to create.

The user can provide values using OS environment variables, but it is also possible to add variables in the clusterctl config file:

# Values for environment variable substitution
AWS_B64ENCODED_CREDENTIALS: XXXXXXXX

In case a variable is defined both in the config file and as an OS environment variable, the latter takes precedence.

Overrides Layer

clusterctl uses an overrides layer to read in injected provider components, cluster templates and metadata. By default, it reads the files from $HOME/.cluster-api/overrides.

The directory structure under the overrides directory should follow the template

<providerType-providerName>/<version>/<fileName>

For example,

├── bootstrap-kubeadm
│   └── v0.3.0
│       └── bootstrap-components.yaml
├── cluster-api
│   └── v0.3.0
│       └── core-components.yaml
├── control-plane-kubeadm
│   └── v0.3.0
│       └── control-plane-components.yaml
└── infrastructure-aws
    └── v0.5.0
            ├── cluster-template-dev.yaml
            └── infrastructure-components.yaml

For developers who want to generate the overrides layer, see Run the local-overrides hack!.

Once these overrides are specified, clusterctl will use them instead of getting the values from the default or specified providers.

One example usage of the overrides layer is that it allows you to deploy clusters with custom templates that may not be available from the official provider repositories. For example, you can now do

clusterctl config cluster mycluster --flavor dev --infrastructure aws:v0.5.0 -v5

The -v5 provides verbose logging which will confirm the usage of the override file.

Using Override="cluster-template-dev.yaml" Provider="infrastructure-aws" Version="v0.5.0"

Another example, if you would like to deploy a custom version of CAPA, you can make changes to infrastructure-components.yaml in the overrides folder and run,

clusterctl init --infrastructure aws:v0.5.0 -v5
...
Using Override="infrastructure-components.yaml" Provider="infrastructure-aws" Version="v0.5.0"
...

If you prefer to have the overrides directory at a different location (e.g. /Users/foobar/workspace/dev-releases) you can specify the overrides directory in the clusterctl config file as

overridesFolder: /Users/foobar/workspace/dev-releases

Image overrides

When working in air-gapped environments, it’s necessary to alter the manifests to be installed in order to pull images from a local/custom image repository instead of public ones (e.g. gcr.io, or quay.io).

The clusterctl configuration file can be used to instruct clusterctl to override images automatically.

This can be achieved by adding an images configuration entry as shown in the example:

images:
  all:
    repository: myorg.io/local-repo

Please note that the image override feature allows for more fine-grained configuration, allowing to set image overrides for specific components, for example:

images:
  all:
    repository: myorg.io/local-repo
  cert-manager:
    tag: v1.1.0

In this example we are overriding the image repository for all the components and the image tag for all the images in the cert-manager component.

If required to alter only a specific image you can use:

images:
  all:
    repository: myorg.io/local-repo
  cert-manager/cert-manager-cainjector:
    tag: v1.1.0

Cert-Manager timeout override

For situations when resources are limited or the network is slow, the cert-manager wait time to be running can be customized by adding a field to the clusterctl config file, for example:

  cert-manager-timeout: 15m

The value string is a possibly signed sequence of decimal numbers, each with optional fraction and a unit suffix, such as “300ms”, “-1.5h” or “2h45m”. Valid time units are “ns”, “us” (or “µs”), “ms”, “s”, “m”, “h”.

If no value is specified or the format is invalid, the default value of 10 minutes will be used.

Debugging/Logging

To have more verbose logs you can use the -v flag when running the clusterctl and set the level of the logging verbose with a positive integer number, ie. -v 3.

If you do not want to use the flag every time you issue a command you can set the environment variable CLUSTERCTL_LOG_LEVEL or set the variable in the clusterctl config file which is located by default at $HOME/.cluster-api/clusterctl.yaml.

clusterctl Provider Contract

The clusterctl command is designed to work with all the providers compliant with the following rules.

Provider Repositories

Each provider MUST define a provider repository, that is a well-known place where the release assets for a provider are published.

The provider repository MUST contain the following files:

• The metadata YAML
• The components YAML

Additionally, the provider repository SHOULD contain the following files:

• Workload cluster templates

Creating a provider repository on GitHub

You can use GitHub release to package your provider artifacts for other people to use.

A github release can be used as a provider repository if:

• The release tag is a valid semantic version number
• The components YAML, the metadata YAML and eventually the workload cluster templates are include into the release assets.

See the GitHub help for more information about how to create a release.

Creating a local provider repository

clusterctl supports reading from a repository defined on the local file system.

A local repository can be defined by creating a <provider-label> folder with a <version> sub-folder for each hosted release; the sub-folder name MUST be a valid semantic version number. e.g.

~/local-repository/infrastructure-aws/v0.5.2

Each version sub-folder MUST contain the corresponding components YAML, the metadata YAML and eventually the workload cluster templates.

Metadata YAML

The provider is required to generate a metadata YAML file and publish it to the provider’s repository.

The metadata YAML file documents the release series of each provider and maps each release series to an API Version of Cluster API (contract).

For example, for Cluster API:

apiVersion: clusterctl.cluster.x-k8s.io/v1alpha3
kind: Metadata
releaseSeries:
- major: 0
  minor: 3
  contract: v1alpha3
- major: 0
  minor: 2
  contract: v1alpha2

Components YAML

The provider is required to generate a components YAML file and publish it to the provider’s repository. This file is a single YAML with all the components required for installing the provider itself (CRDs, Controller, RBAC etc.).

The following rules apply:

Naming conventions

It is strongly recommended that:

• Core provider release a file called core-components.yaml
• Infrastructure providers release a file called infrastructure-components.yaml
• Bootstrap providers release a file called bootstrap-components.yaml
• Control plane providers release a file called control-plane-components.yaml

Shared and instance components

The objects contained in a component YAML file can be divided in two sets:

• Instance specific objects, like the Deployment for the controller, the ServiceAccount used for running the controller and the related RBAC rules.
• The objects that are shared among all the provider instances, like e.g. CRDs, ValidatingWebhookConfiguration or the Deployment implementing the web-hook servers and related Service and Certificates.

As per the Cluster API contract, all the shared objects are expected to be deployed in a namespace named capi-webhook-system (if applicable).

clusterctl implements a different lifecycle for shared resources e.g.

• ensuring that the version of the shared objects for each provider matches the latest version installed in the cluster.
• ensuring that deleting an instance of a provider does not destroy shared resources unless explicitly requested by the user.

Target namespace

The instance components should contain one Namespace object, which will be used as the default target namespace when creating the provider components.

All the objects in the components YAML MUST belong to the target namespace, with the exception of objects that are not namespaced, like ClusterRoles/ClusterRoleBinding and CRD objects.

Controllers & Watching namespace

Each provider is expected to deploy controllers using a Deployment.

While defining the Deployment Spec, the container that executes the controller binary MUST be called manager.

The manager MUST support a --namespace flag for specifying the namespace where the controller will look for objects to reconcile.

Variables

The components YAML can contain environment variables matching the format ${VAR}; it is highly recommended to prefix the variable name with the provider name e.g. ${AWS_CREDENTIALS}

clusterctl uses the library drone/envsubst to perform variable substitution.

# If `VAR` is not set or empty, the default value is used. This is true for
all the following formats.
${VAR:=default}
${VAR=default}
${VAR:-default}

Other functions such as substring replacement are also supported by the library. See drone/envsubst for more information.

Additionally, each provider should create user facing documentation with the list of required variables and with all the additional notes that are required to assist the user in defining the value for each variable.

Labels

The components YAML components should be labeled with cluster.x-k8s.io/provider and the name of the provider. This will enable an easier transition from kubectl apply to clusterctl.

As a reference you can consider the labels applied to the following providers.

Workload cluster templates

An infrastructure provider could publish a cluster templates file to be used by clusterctl config cluster. This is single YAML with all the objects required to create a new workload cluster.

The following rules apply:

Naming conventions

Cluster templates MUST be stored in the same folder as the component YAML and follow this naming convention:

1. The default cluster template should be named cluster-template.yaml.
2. Additional cluster template should be named cluster-template-{flavor}.yaml. e.g cluster-template-prod.yaml

{flavor} is the name the user can pass to the clusterctl config cluster --flavor flag to identify the specific template to use.

Each provider SHOULD create user facing documentation with the list of available cluster templates.

Target namespace

The cluster template YAML MUST assume the target namespace already exists.

All the objects in the cluster template YAML MUST be deployed in the same namespace.

Variables

The cluster templates YAML can also contain environment variables (as can the components YAML).

Additionally, each provider should create user facing documentation with the list of required variables and with all the additional notes that are required to assist the user in defining the value for each variable.

Common variables

The clusterctl config cluster command allows user to set a small set of common variables via CLI flags or command arguments.

Templates writers should use the common variables to ensure consistency across providers and a simpler user experience (if compared to the usage of OS environment variables or the clusterctl config file).

Additionally, value of the command argument to clusterctl config cluster <cluster-name> (<cluster-name> in this case), will be applied to every occurrence of the ${ CLUSTER_NAME } variable.

OwnerReferences chain

Each provider is responsible to ensure that all the providers resources (like e.g. VSphereCluster, VSphereMachine, VSphereVM etc. for the vsphere provider) MUST have a Metadata.OwnerReferences entry that links directly or indirectly to a Cluster object.

Please note that all the provider specific resources that are referenced by the Cluster API core objects will get the OwnerReference sets by the Cluster API core controllers, e.g.:

• The Cluster controller ensures that all the objects referenced in Cluster.Spec.InfrastructureRef get an OwnerReference that links directly to the corresponding Cluster.
• The Machine controller ensures that all the objects referenced in Machine.Spec.InfrastructureRef get an OwnerReference that links to the corresponding Machine, and the Machine is linked to the Cluster through its own OwnerReference chain.

That means that, practically speaking, provider implementers are responsible for ensuring that the OwnerReferences are set only for objects that are not directly referenced by Cluster API core objects, e.g.:

• All the VSphereVM instances should get an OwnerReference that links to the corresponding VSphereMachine, and the VSphereMachine is linked to the Cluster through its own OwnerReference chain.

Additional notes

Components YAML transformations

Provider authors should be aware of the following transformations that clusterctl applies during component installation:

• Variable substitution;
• Enforcement of target namespace:
  • The name of the namespace object is set;
  • The namespace field of all the objects is set (with exception of cluster wide objects like e.g. ClusterRoles);
  • ClusterRole and ClusterRoleBinding are renamed by adding a “${namespace}-“ prefix to the name; this change reduces the risks of conflicts between several instances of the same provider in case of multi tenancy;
• Enforcement of watching namespace;
• All components are labeled;

Cluster template transformations

Provider authors should be aware of the following transformations that clusterctl applies during components installation:

• Variable substitution;
• Enforcement of target namespace:
  • The namespace field of all the objects is set;

Links to external objects

The clusterctl command requires that both the components YAML and the cluster templates contain all the required objects.

If, for any reason, the provider authors/YAML designers decide not to comply with this recommendation and e.g. to

• implement links to external objects from a component YAML (e.g. secrets, aggregated ClusterRoles NOT included in the component YAML)
• implement link to external objects from a cluster template (e.g. secrets, configMaps NOT included in the cluster template)

The provider authors/YAML designers should be aware that it is their responsibility to ensure the proper functioning of all the clusterctl features both in single tenancy or multi-tenancy scenarios and/or document known limitations.

Move

Provider authors should be aware that clusterctl move command implements a discovery mechanism that considers:

• All the objects of Kind defined in one of the CRDs installed by clusterctl using clusterctl init.
• Secret and ConfigMap objects.
• The OwnerReference chain of the above objects.
• Any object of Kind in which its CRD has the “move” label (clusterctl.cluster.x-k8s.io/move) attached to it.

clusterctl move does NOT consider any objects:

• Not included in the set of objects defined above.
• Included in the set of objects defined above, but not:
  • Directly or indirectly linked to a Cluster object through the OwnerReference chain.
  • Directly or indirectly linked to a ClusterResourceSet object through the OwnerReference chain.

If moving some of excluded object is required, the provider authors should create documentation describing the the exact move sequence to be executed by the user.

Additionally, provider authors should be aware that clusterctl move assumes all the provider’s Controllers respect the Cluster.Spec.Paused field introduced in the v1alpha3 Cluster API specification.

clusterctl for Developers

This document describes how to use clusterctl during the development workflow.

Prerequisites

• A Cluster API development setup (go, git, kind v0.9 or newer, Docker v19.03 or newer etc.)
• A local clone of the Cluster API GitHub repository
• A local clone of the GitHub repositories for the providers you want to install

Build clusterctl

From the root of the local copy of Cluster API, you can build the clusterctl binary by running:

make clusterctl

The output of the build is saved in the bin/ folder; In order to use it you have to specify the full path, create an alias or copy it into a folder under your $PATH.

Use local artifacts

Clusterctl by default uses artifacts published in the providers repositories; during the development workflow it might happen you want to use artifacts from your local workstation.

There are two options to do so:

• Use the overrides layer, when you want to override a single published artifact with a local one.
• Create a local repository, when you want to avoid to use published artifacts and use intead the local ones.

If you want to create a local artifact, follow those instructions:

Build artifacts locally

In order to build artifacts for the CAPI core provider, the kubeadm bootstrap provider and the kubeadm control plane provider:

make docker-build REGISTRY=gcr.io/k8s-staging-cluster-api
make generate-manifests REGISTRY=gcr.io/k8s-staging-cluster-api PULL_POLICY=IfNotPresent

In order to build docker provider artifacts

make -C test/infrastructure/docker docker-build REGISTRY=gcr.io/k8s-staging-cluster-api
make -C test/infrastructure/docker generate-manifests REGISTRY=gcr.io/k8s-staging-cluster-api PULL_POLICY=IfNotPresent

Create a clusterctl-settings.json file

Next, create a clusterctl-settings.json file and place it in your local copy of Cluster API. This file will be used by create-local-repository.py. Here is an example:

{
  "providers": ["cluster-api","bootstrap-kubeadm","control-plane-kubeadm", "infrastructure-aws", "infrastructure-docker"],
  "provider_repos": ["../cluster-api-provider-aws"]
}

providers (Array[]String, default=[]): A list of the providers to enable. See available providers for more details.

provider_repos (Array[]String, default=[]): A list of paths to all the providers you want to use. Each provider must have a clusterctl-settings.json file describing how to build the provider assets.

Create the local repository

Run the create-local-repository hack from the root of the local copy of Cluster API:

cmd/clusterctl/hack/create-local-repository.py

The script reads from the source folders for the providers you want to install, builds the providers’ assets, and places them in a local repository folder located under $HOME/.cluster-api/dev-repository/. Additionally, the command output provides you the clusterctl init command with all the necessary flags. The output should be similar to:

clusterctl local overrides generated from local repositories for the cluster-api, bootstrap-kubeadm, control-plane-kubeadm, infrastructure-docker, infrastructure-aws providers.
in order to use them, please run:

clusterctl init \
   --core cluster-api:v0.3.8 \
   --bootstrap kubeadm:v0.3.8 \
   --control-plane kubeadm:v0.3.8 \
   --infrastructure aws:v0.5.0 \
   --infrastructure docker:v0.3.8 \
   --config ~/.cluster-api/dev-repository/config.yaml

As you might notice, the command is using the $HOME/.cluster-api/dev-repository/config.yaml config file, containing all the required setting to make clusterctl use the local repository.

Available providers

The following providers are currently defined in the script:

• cluster-api
• bootstrap-kubeadm
• control-plane-kubeadm
• infrastructure-docker

More providers can be added by editing the clusterctl-settings.json in your local copy of Cluster API; please note that each provider_repo should have its own clusterctl-settings.json describing how to build the provider assets, e.g.

{
  "name": "infrastructure-aws",
  "config": {
    "componentsFile": "infrastructure-components.yaml",
    "nextVersion": "v0.5.0",
  }
}

Create a kind management cluster

kind can provide a Kubernetes cluster to be used a management cluster. See Install and/or configure a kubernetes cluster for more about how.

Before running clusterctl init, you must ensure all the required images are available in the kind cluster.

This is always the case for images published in some image repository like docker hub or gcr.io, but it can’t be the case for images built locally; in this case, you can use kind load to move the images built locally. e.g

kind load docker-image gcr.io/k8s-staging-cluster-api/cluster-api-controller-amd64:dev
kind load docker-image gcr.io/k8s-staging-cluster-api/kubeadm-bootstrap-controller-amd64:dev
kind load docker-image gcr.io/k8s-staging-cluster-api/kubeadm-control-plane-controller-amd64:dev
kind load docker-image gcr.io/k8s-staging-cluster-api/capd-manager-amd64:dev

to make the controller images available for the kubelet in the management cluster.

When the kind cluster is ready and all the required images are in place, run the clusterctl init command generated by the create-local-repository.py script.

Optionally, you may want to check if the components are running properly. The exact components depend on which providers you have initialized. Below is an example with an installed Docker provider (CAPD).

kubectl get deploy -A | grep  "cap\|cert"
capd-system                         capd-controller-manager                         1/1     1            1           25m
capi-kubeadm-bootstrap-system       capi-kubeadm-bootstrap-controller-manager       1/1     1            1           25m
capi-kubeadm-control-plane-system   capi-kubeadm-control-plane-controller-manager   1/1     1            1           25m
capi-system                         capi-controller-manager                         1/1     1            1           25m
cert-manager                        cert-manager                                    1/1     1            1           27m
cert-manager                        cert-manager-cainjector                         1/1     1            1           27m
cert-manager                        cert-manager-webhook                            1/1     1            1           27m

Additional Notes for the Docker Provider

The command for getting the kubeconfig file for connecting to a workload cluster is the following:

clusterctl get kubeconfig capi-quickstart > capi-quickstart.kubeconfig

When using docker on MacOS, you will need to do a couple of additional steps to get the correct kubeconfig for a workload cluster created with the docker provider:

# Point the kubeconfig to the exposed port of the load balancer, rather than the inaccessible container IP.
sed -i -e "s/server:.*/server: https:\/\/$(docker port capi-quickstart-lb 6443/tcp | sed "s/0.0.0.0/127.0.0.1/")/g" ./capi-quickstart.kubeconfig

# Ignore the CA, because it is not signed for 127.0.0.1
sed -i -e "s/certificate-authority-data:.*/insecure-skip-tls-verify: true/g" ./capi-quickstart.kubeconfig

Developer Guide

Pieces of Cluster API

Cluster API is made up of many components, all of which need to be running for correct operation. For example, if you wanted to use Cluster API with AWS, you’d need to install both the cluster-api manager and the aws manager.

Cluster API includes a built-in provisioner, Docker, that’s suitable for using for testing and development. This guide will walk you through getting that daemon, known as [CAPD], up and running.

Other providers may have additional steps you need to follow to get up and running.

Prerequisites

Docker

Iterating on the cluster API involves repeatedly building Docker containers. You’ll need the docker daemon v19.03 or newer available.

A Cluster

You’ll likely want an existing cluster as your management cluster. The easiest way to do this is with kind v0.9 or newer, as explained in the quick start.

Make sure your cluster is set as the default for kubectl. If it’s not, you will need to modify subsequent kubectl commands below.

A container registry

If you’re using kind, you’ll need a way to push your images to a registry to they can be pulled. You can instead side-load all images, but the registry workflow is lower-friction.

Most users test with GCR, but you could also use something like Docker Hub. If you choose not to use GCR, you’ll need to set the REGISTRY environment variable.

Kustomize

You’ll need to install kustomize. There is a version of kustomize built into kubectl, but it does not have all the features of kustomize v3 and will not work.

Kubebuilder

You’ll need to install kubebuilder.

Envsubst

You’ll need drone/envsubst or similar to handle clusterctl var replacement. envsubst in GNU gettext package is insufficient and we’ve noticed some parsing differences, e.g. when parsing a YAML configuration file containing variables with default values. Note: drone/envsubst releases v1.0.2 and earlier do not have the binary packaged under cmd/envsubst. It is available in Go psuedo-version v1.0.3-0.20200709231038-aa43e1c1a629

We provide a make target to generate the envsubst binary if desired. See the provider contract for more details about how clusterctl uses variables.

make envsubst

The generated binary can be found at ./hack/tools/bin/envsubst

Cert-Manager

You’ll need to deploy cert-manager components on your management cluster, using kubectl

kubectl apply -f https://github.com/jetstack/cert-manager/releases/download/v1.1.0/cert-manager.yaml

Ensure the cert-manager webhook service is ready before creating the Cluster API components.

This can be done by running:

kubectl wait --for=condition=Available --timeout=300s apiservice v1beta1.webhook.cert-manager.io

Development

Option 1: Tilt

Tilt is a tool for quickly building, pushing, and reloading Docker containers as part of a Kubernetes deployment. Many of the Cluster API engineers use it for quick iteration. Please see our Tilt instructions to get started.

Option 2: The Old-fashioned way

Building everything

You’ll need to build two docker images, one for Cluster API itself and one for the Docker provider (CAPD).

make docker-build
make -C test/infrastructure/docker docker-build

Push both images

$ make docker-push
docker push gcr.io/cluster-api-242700/cluster-api-controller-amd64:dev
The push refers to repository [gcr.io/cluster-api-242700/cluster-api-controller-amd64]
90a39583ad5f: Layer already exists
932da5156413: Layer already exists
dev: digest: sha256:263262cfbabd3d1add68172a5a1d141f6481a2bc443672ce80778dc122ee6234 size: 739
$ make -C test/infrastructure/docker docker-push
make: Entering directory '/home/liz/src/sigs.k8s.io/cluster-api/test/infrastructure/docker'
docker push gcr.io/cluster-api-242700/manager:dev
The push refers to repository [gcr.io/cluster-api-242700/manager]
5b1e744b2bae: Pushed
932da5156413: Layer already exists
dev: digest: sha256:35670a049372ae063dad910c267a4450758a139c4deb248c04c3198865589ab2 size: 739
make: Leaving directory '/home/liz/src/sigs.k8s.io/cluster-api/test/infrastructure/docker'

Make a note of the URLs and the digests. You’ll need them for the next step. In this case, they’re...

gcr.io/cluster-api-242700/manager@sha256:35670a049372ae063dad910c267a4450758a139c4deb248c04c3198865589ab2

and

gcr.io/cluster-api-242700/cluster-api-controller-amd64@sha256:263262cfbabd3d1add68172a5a1d141f6481a2bc443672ce80778dc122ee6234

Edit the manifests

$EDITOR config/manager/manager_image_patch.yaml
$EDITOR test/infrastructure/docker/config/manager/manager_image_patch.yaml

In both cases, change the - image: url to the digest URL mentioned above:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: controller-manager
  namespace: system
spec:
  template:
    spec:
      containers:
      - image: gcr.io/cluster-api-242700/manager@sha256:35670a049372ae063dad910c267a4450758a139c4deb248c04c3198865589ab2`
        name: manager

Apply the manifests

$ kustomize build config/ | ./hack/tools/bin/envsubst | kubectl apply -f -
namespace/capi-system configured
customresourcedefinition.apiextensions.k8s.io/clusters.cluster.x-k8s.io configured
customresourcedefinition.apiextensions.k8s.io/kubeadmconfigs.bootstrap.cluster.x-k8s.io configured
customresourcedefinition.apiextensions.k8s.io/kubeadmconfigtemplates.bootstrap.cluster.x-k8s.io configured
customresourcedefinition.apiextensions.k8s.io/machinedeployments.cluster.x-k8s.io configured
customresourcedefinition.apiextensions.k8s.io/machines.cluster.x-k8s.io configured
customresourcedefinition.apiextensions.k8s.io/machinesets.cluster.x-k8s.io configured
role.rbac.authorization.k8s.io/capi-leader-election-role configured
clusterrole.rbac.authorization.k8s.io/capi-manager-role configured
rolebinding.rbac.authorization.k8s.io/capi-leader-election-rolebinding configured
clusterrolebinding.rbac.authorization.k8s.io/capi-manager-rolebinding configured
deployment.apps/capi-controller-manager created

$ kustomize build test/infrastructure/docker/config | ./hack/tools/bin/envsubst | kubectl apply -f -
namespace/capd-system configured
customresourcedefinition.apiextensions.k8s.io/dockerclusters.infrastructure.cluster.x-k8s.io configured
customresourcedefinition.apiextensions.k8s.io/dockermachines.infrastructure.cluster.x-k8s.io configured
customresourcedefinition.apiextensions.k8s.io/dockermachinetemplates.infrastructure.cluster.x-k8s.io configured
role.rbac.authorization.k8s.io/capd-leader-election-role configured
clusterrole.rbac.authorization.k8s.io/capd-manager-role configured
clusterrole.rbac.authorization.k8s.io/capd-proxy-role configured
rolebinding.rbac.authorization.k8s.io/capd-leader-election-rolebinding configured
clusterrolebinding.rbac.authorization.k8s.io/capd-manager-rolebinding configured
clusterrolebinding.rbac.authorization.k8s.io/capd-proxy-rolebinding configured
service/capd-controller-manager-metrics-service created
deployment.apps/capd-controller-manager created

Check the status of the clusters

$ kubectl get po -n capd-system
NAME                                       READY   STATUS    RESTARTS   AGE
capd-controller-manager-7568c55d65-ndpts   2/2     Running   0          71s
$ kubectl get po -n capi-system
NAME                                      READY   STATUS    RESTARTS   AGE
capi-controller-manager-bf9c6468c-d6msj   1/1     Running   0          2m9s

Testing

Cluster API has a number of test suites available for you to run. Please visit the testing page for more information on each suite.

That’s it!

Now you can create CAPI objects! To test another iteration, you’ll need to follow the steps to build, push, update the manifests, and apply.

Repository Layout

This page is still being written - stay tuned!

Developing Cluster API with Tilt

Overview

This document describes how to use kind and Tilt for a simplified workflow that offers easy deployments and rapid iterative builds.

Prerequisites

1. Docker v19.03 or newer
2. kind v0.9 or newer (other clusters can be used if preload_images_for_kind is set to false)
3. kustomize standalone (kubectl kustomize does not work because it is missing some features of kustomize v3)
4. Tilt v0.12.0 or newer
5. envsubst or similar to handle clusterctl var replacement. Note: drone/envsubst releases v1.0.2 and earlier do not have the binary packaged under cmd/envsubst. It is available in Go psuedo-version v1.0.3-0.20200709231038-aa43e1c1a629
6. Clone the Cluster API repository locally
7. Clone the provider(s) you want to deploy locally as well

We provide a make target to generate the envsubst binary if desired. See the provider contract for more details about how clusterctl uses variables.

make envsubst

Getting started

Create a kind cluster

First, make sure you have a kind cluster and that your KUBECONFIG is set up correctly:

kind create cluster

Create a tilt-settings.json file

Next, create a tilt-settings.json file and place it in your local copy of cluster-api. Here is an example:

{
  "default_registry": "gcr.io/your-project-name-here",
  "provider_repos": ["../cluster-api-provider-aws"],
  "enable_providers": ["aws", "docker", "kubeadm-bootstrap", "kubeadm-control-plane"]
}

tilt-settings.json fields

allowed_contexts (Array, default=[]): A list of kubeconfig contexts Tilt is allowed to use. See the Tilt documentation on *allow_k8s_contexts for more details.

default_registry (String, default=””): The image registry to use if you need to push images. See the Tilt *documentation for more details.

provider_repos (Array[]String, default=[]): A list of paths to all the providers you want to use. Each provider must have a tilt-provider.json file describing how to build the provider.

enable_providers (Array[]String, default=[‘docker’]): A list of the providers to enable. See available providers for more details.

kind_cluster_name (String, default=”kind”): The name of the kind cluster to use when preloading images.

kustomize_substitutions (Map{String: String}, default={}): An optional map of substitutions for ${}-style placeholders in the provider’s yaml.

"kustomize_substitutions": {
  "AWS_B64ENCODED_CREDENTIALS": "your credentials here"
}

AZURE_SUBSCRIPTION_ID=$(az account show --query id --output tsv)
az account set --subscription $AZURE_SUBSCRIPTION_ID

AZURE_SERVICE_PRINCIPAL_NAME=ServicePrincipalName

AZURE_TENANT_ID=$( az account show --query tenantId --output tsv)
AZURE_CLIENT_SECRET=$(az ad sp create-for-rbac --name http://$AZURE_SERVICE_PRINCIPAL_NAME --query password --output tsv)
AZURE_CLIENT_ID=$(az ad sp show --id http://$AZURE_SERVICE_PRINCIPAL_NAME --query appId --output tsv)

cat <<EOF
"kustomize_substitutions": {
   "AZURE_SUBSCRIPTION_ID_B64": "$(echo "${AZURE_SUBSCRIPTION_ID}" | tr -d '\n' | base64 | tr -d '\n')",
   "AZURE_TENANT_ID_B64": "$(echo "${AZURE_TENANT_ID}" | tr -d '\n' | base64 | tr -d '\n')",
   "AZURE_CLIENT_SECRET_B64": "$(echo "${AZURE_CLIENT_SECRET}" | tr -d '\n' | base64 | tr -d '\n')",
   "AZURE_CLIENT_ID_B64": "$(echo "${AZURE_CLIENT_ID}" | tr -d '\n' | base64 | tr -d '\n')"
  }
EOF

base64 -i ~/path/to/gcp/credentials.json

"kustomize_substitutions": {
  "GCP_B64ENCODED_CREDENTIALS": "your credentials here"
}

deploy_cert_manager (Boolean, default=true): Deploys cert-manager into the cluster for use for webhook registration.

preload_images_for_kind (Boolean, default=true): Uses kind load docker-image to preload images into a kind cluster.

trigger_mode (String, default=auto): Optional setting to configure if tilt should automatically rebuild on changes. Set to manual to disable auto-rebuilding and require users to trigger rebuilds of individual changed components through the UI.

extra_args (Object, default={}): A mapping of provider to additional arguments to pass to the main binary configured for this provider. Each item in the array will be passed in to the manager for the given provider.

Example:

{
    "extra_args": {
        "core": ["--feature-gates=MachinePool=true"],
        "kubeadm-bootstrap": ["--feature-gates=MachinePool=true"],
        "azure": ["--feature-gates=MachinePool=true"]
    }
}

With this config, the respective managers will be invoked with:

manager --feature-gates=MachinePool=true

Run Tilt!

To launch your development environment, run

tilt up

This will open the command-line HUD as well as a web browser interface. You can monitor Tilt’s status in either location. After a brief amount of time, you should have a running development environment, and you should now be able to create a cluster. Please see the Usage section in the Quick Start for more information on creating workload clusters.

Available providers

The following providers are currently defined in the Tiltfile:

• core: cluster-api itself (Cluster/Machine/MachineDeployment/MachineSet/KubeadmConfig/KubeadmControlPlane)
• docker: Docker provider (DockerCluster/DockerMachine)

tilt-provider.json

A provider must supply a tilt-provider.json file describing how to build it. Here is an example:

{
    "name": "aws",
    "config": {
        "image": "gcr.io/k8s-staging-cluster-api-aws/cluster-api-aws-controller",
        "live_reload_deps": [
            "main.go", "go.mod", "go.sum", "api", "cmd", "controllers", "pkg"
        ]
    }
}

config fields

image: the image for this provider, as referenced in the kustomize files. This must match; otherwise, Tilt won’t build it.

live_reload_deps: a list of files/directories to watch. If any of them changes, Tilt rebuilds the manager binary for the provider and performs a live update of the running container.

additional_docker_helper_commands (String, default=””): Additional commands to be run in the helper image docker build. e.g.

RUN wget -qO- https://dl.k8s.io/v1.14.4/kubernetes-client-linux-amd64.tar.gz | tar xvz
RUN wget -qO- https://get.docker.com | sh

additional_docker_build_commands (String, default=””): Additional commands to be appended to the dockerfile. The manager image will use docker-slim, so to download files, use additional_helper_image_commands. e.g.

COPY --from=tilt-helper /usr/bin/docker /usr/bin/docker
COPY --from=tilt-helper /go/kubernetes/client/bin/kubectl /usr/bin/kubectl

kustomize_config (Bool, default=true): Whether or not running kustomize on the ./config folder of the provider. Set to false if your provider does not have a ./config folder or you do not want it to be applied in the cluster.

go_main (String, default=”main.go”): The go main file if not located at the root of the folder

Customizing Tilt

If you need to customize Tilt’s behavior, you can create files in cluster-api’s tilt.d directory. This file is ignored by git so you can be assured that any files you place here will never be checked in to source control.

These files are included after the providers map has been defined and after all the helper function definitions. This is immediately before the “real work” happens.

Under the covers, a.k.a “the real work”

At a high level, the Tiltfile performs the following actions:

1. Read tilt-settings.json
2. Configure the allowed Kubernetes contexts
3. Set the default registry
4. Define the providers map
5. Include user-defined Tilt files
6. Deploy cert-manager
7. Enable providers (core + what is listed in tilt-settings.json)
   1. Build the manager binary locally as a local_resource
   2. Invoke docker_build for the provider
   3. Invoke kustomize for the provider’s config/ directory

Live updates

Each provider in the providers map has a live_reload_deps list. This defines the files and/or directories that Tilt should monitor for changes. When a dependency is modified, Tilt rebuilds the provider’s manager binary on your local machine, copies the binary to the running container, and executes a restart script. This is significantly faster than rebuilding the container image for each change. It also helps keep the size of each development image as small as possible (the container images do not need the entire go toolchain, source code, module dependencies, etc.).

Testing Cluster API

This document presents testing guideline and conventions for Cluster API.

IMPORTANT: improving and maintaining this document is a collaborative effort, so we are encouraging constructive feedback and suggestions.

Unit tests

Unit tests focus on individual pieces of logic - a single func - and don’t require any additional services to execute. They should be fast and great for getting the first signal on the current implementation, but unit test have the risk that to allow integration bugs to slip through.

Historically, in Cluster API unit test were developed using go test, gomega and the fakeclient; see the quick reference below.

However, considered some changes introduced in the v0.3.x releases (e.g. ObservedGeneration, Conditions), there is a common agreement among Cluster API maintainers that usage fakeclient should be progressively deprecated in favor of usage of envtest; see the quick reference below.

Integration tests

Integration tests are focuses on testing the behavior of an entire controller or the interactions between two or more Cluster API controllers.

In older versions of Cluster API, integration test were based on a real cluster and meant to be run in CI only; however, now we are considering a different approach base on envtest and with one or more controllers configured to run against the test cluster.

With this approach it is possible to interact with Cluster API like in a real environment, by creating/updating Kubernetes objects and waiting for the controllers to take action.

Please note that while using this mode, as of today, when testing the interactions with an infrastructure provider some infrastructure components will be generated, and this could have relevant impacts on test durations (and requirements).

While, as of today this is a strong limitation, in the future we might consider to have a “dry-run” option in CAPD or a fake infrastructure provider to allow test coverage for testing the interactions with an infrastructure provider as well.

Running unit and integration tests

Using the test target through make will run all of the unit and integration tests.

End-to-end tests

The end-to-end tests are meant to verify the proper functioning of a Cluster API management cluster in an environment that resemble a real production environment.

Following guidelines should be followed when developing E2E tests:

• Use the [Cluster API test framework].
• Define test spec reflecting real user workflow, e.g. [Cluster API quick start].
• Unless you are testing provider specific features, ensure your test can run with different infrastructure providers (see Writing Portable Tests).

See e2e development for more information on developing e2e tests for CAPI and external providers.

Running the end-to-end tests

make docker-build-e2e will build the images for all providers that will be needed for the e2e test.

make test-e2e will run e2e tests by using whatever provider images already exist on disk. After running make docker-build-e2e at least once, this can be used for a faster test run if there are no provider code changes.

Additionally, test-e2e target supports the following env variables:

• GINKGO_FOCUS to set ginkgo focus (default empty - all tests)
• GINKGO_NODES to set the number of ginkgo parallel nodes (default to 1)
• E2E_CONF_FILE to set the e2e test config file (default to ${REPO_ROOT}/test/e2e/config/docker.yaml)
• ARTIFACTS to set the folder where test artifact will be stored (default to ${REPO_ROOT}/_artifacts)
• SKIP_RESOURCE_CLEANUP to skip resource cleanup at the end of the test (useful for problem investigation) (default to false)
• USE_EXISTING_CLUSTER to use an existing management cluster instead of creating a new one for each test run (default to false)
• GINKGO_NOCOLOR to turn off the ginko colored output (default to false)

Quick reference

envtest

envtest is a testing environment that is provided by the controller-runtime project. This environment spins up a local instance of etcd and the kube-apiserver. This allows test to be executed in an environment very similar to a real environment.

Additionally, in Cluster API there is a set of utilities under test/helpers that helps developers in setting up a envtest ready for Cluster API testing, and most specifically:

• With the required CRDs already pre-configured.
• With all the Cluster API webhook pre-configured, so there are enforced guarantees about the semantic accuracy of the test objects you are going to create.

This is an example of how to create an instance of envtest that can be shared across all the tests in a package; by convention, this code should be in a file named suite_test.go:

var (
	testEnv *helpers.TestEnvironment
	ctx     = context.Background()
)

func TestMain(m *testing.M) {
	// Bootstrapping test environment
	testEnv = helpers.NewTestEnvironment()
	go func() {
		if err := testEnv.StartManager(); err != nil {
			panic(fmt.Sprintf("Failed to start the envtest manager: %v", err))
		}
	}()
	// Run tests
	code := m.Run()
	// Tearing down the test environment
	if err := testEnv.Stop(); err != nil {
		panic(fmt.Sprintf("Failed to stop the envtest: %v", err))
	}

	// Report exit code
	os.Exit(code)
}

Most notably, envtest provides not only a real API server to user during test, but it offers the opportunity to configure one or more controllers to run against the test cluster; by using this feature it is possible to use envtest for developing Cluster API integration tests.

func TestMain(m *testing.M) {
	// Bootstrapping test environment
	...
	
	if err := (&MyReconciler{
		Client:  testEnv,
		Log:     log.NullLogger{},
	}).SetupWithManager(testEnv.Manager, controller.Options{MaxConcurrentReconciles: 1}); err != nil {
		panic(fmt.Sprintf("Failed to start the MyReconciler: %v", err))
	}

	// Run tests
	...
}

Please note that, because envtest uses a real kube-apiserver that is shared across many tests, the developer should take care of ensuring each test run in isolation from the others, by:

• Creating objects in separated namespaces.
• Avoiding object name conflict.

However, developers should be aware that in some ways, the test control plane will behave differently from “real” clusters, and that might have an impact on how you write tests.

One common example is garbage collection; because there are no controllers monitoring built-in resources, objects do not get deleted, even if an OwnerReference is set up; as a consequence, usually test implements code for cleaning up created objects.

This is an example of a test implementing those recommendations:

func TestAFunc(t *testing.T) {
	g := NewWithT(t)
	// Generate namespace with a random name starting with ns1; such namespace
	// will host test objects in isolation from other tests.
	ns1, err := testEnv.CreateNamespace(ctx, "ns1") 
	g.Expect(err).ToNot(HaveOccurred())
	defer func() {
		// Cleanup the test namespace
		g.Expect(testEnv.DeleteNamespace(ctx, ns1)).To(Succeed())
	}()

	obj := &clusterv1.Cluster{
		ObjectMeta: metav1.ObjectMeta{
			Name:      "test",
			Namespace: ns1.Name, // Place test objects in the test namespace
		},
	}
	
	// Actual test code...
}

In case of object used in many test case within the same test, it is possible to leverage on Kubernetes GenerateName; For objects that are shared across sub-tests, ensure they are scoped within the test namespace and deep copied to avoid cross-test changes that may occur to the object.

func TestAFunc(t *testing.T) {
	g := NewWithT(t)
	// Generate namespace with a random name starting with ns1; such namespace
	// will host test objects in isolation from other tests.
	ns1, err := testEnv.CreateNamespace(ctx, "ns1") 
	g.Expect(err).ToNot(HaveOccurred())
	defer func() {
		// Cleanup the test namespace
		g.Expect(testEnv.DeleteNamespace(ctx, ns1)).To(Succeed())
	}()

	obj := &clusterv1.Cluster{
		ObjectMeta: metav1.ObjectMeta{
			GenerateName: "test-",  // Instead of assigning a name, use GenerateName
			Namespace:    ns1.Name, // Place test objects in the test namespace
		},
	}
	
	t.Run("test case 1", func(t *testing.T) {
		g := NewWithT(t)
		// Deep copy the object in each test case, so we prevent side effects in case the object changes.
		// Additionally, thanks to GenerateName, the objects gets a new name for each test case.
		obj := obj.DeepCopy()

	    // Actual test case code...
	}
	t.Run("test case 2", func(t *testing.T) {
		g := NewWithT(t)
		obj := obj.DeepCopy()

	    // Actual test case code...
	}
	// More test cases.
}

fakeclient

fakeclient is another utility that is provided by the controller-runtime project. While this utility is really fast and simple to use because it does not require to spin-up an instance of etcd and kube-apiserver, the fakeclient comes with a set of limitations that could hamper the validity of a test, most notably:

• it does not handle properly a set of field which are common in the Kubernetes API objects (and Cluster API objects as well) like e.g. creationTimestamp, resourceVersion, generation, uid
• API calls does not execute defaulting or validation webhooks, so there are no enforced guarantee about the semantic accuracy of the test objects.

Historically, fakeclient is widely used in Cluster API, however, given the growing relevance of the above limitations with regard to some changes introduced in the v0.3.x releases (e.g. ObservedGeneration, Conditions), there is a common agreement among Cluster API maintainers that usage fakeclient should be progressively deprecated in favor of usage of envtest.

ginkgo

Ginkgo is a Go testing framework built to help you efficiently write expressive and comprehensive tests using Behavior-Driven Development (“BDD”) style.

While Ginkgo is widely used in the Kubernetes ecosystem, Cluster API maintainers found the lack of integration with the most used golang IDE somehow limiting, mostly because:

• it makes interactive debugging of tests more difficult, since you can’t just run the test using the debugger directly
• it makes it more difficult to only run a subset of tests, since you can’t just run or debug individual tests using an IDE, but you now need to run the tests using make or the ginkgo command line and override the focus to select individual tests

In Cluster API you MUST use ginkgo only for E2E tests, where it is required to leverage on the support for running specs in parallel; in any case, developers MUST NOT use the table driven extension DSL (DescribeTable, Entry commands) which is considered unintuitive.

gomega

Gomega is a matcher/assertion library. It is usually paired with the Ginkgo BDD test framework, but it can be used with other test frameworks too.

More specifically, in order to use Gomega with go test you should

func TestFarmHasCow(t *testing.T) {
    g := NewWithT(t)
    g.Expect(f.HasCow()).To(BeTrue(), "Farm should have cow")
}

In Cluster API all the test MUST use Gomega assertions.

go test

go test testing provides support for automated testing of Go packages.

In Cluster API Unit and integration test MUST use go test.

Developing E2E tests

E2E tests are meant to verify the proper functioning of a Cluster API management cluster in an environment that resemble a real production environment.

Following guidelines should be followed when developing E2E tests:

• Use the Cluster API test framework.
• Define test spec reflecting real user workflow, e.g. Cluster API quick start.
• Unless you are testing provider specific features, ensure your test can run with different infrastructure providers (see Writing Portable Tests).

The Cluster API test framework provides you a set of helpers method for getting your test in place quickly; the test E2E package provide examples of how this can be achieved and reusable test specs for the most common Cluster API use cases.

Prerequisites

Each E2E test requires a set of artifacts to be available:

• Binaries & docker images for Kubernetes, CNI, CRI & CSI
• Manifests & docker images for the Cluster API core components
• Manifests & docker images for the Cluster API infrastructure provider; in most cases also machine images are required (AMI, OVA etc.)
• Credentials for the target infrastructure provider
• Other support tools (e.g. kustomize, gsutil etc.)

The Cluster API test framework provides support for building and retrieving the manifest files for Cluster API core components and for the Cluster API infrastructure provider (see Setup)

For the remaining tasks you can find examples of how this can be implemented e.g. in CAPA E2E tests and CAPG E2E tests.

Setup

In order to run E2E tests it is required to create a Kubernetes cluster with a complete set of Cluster API providers installed. Setting up those elements is usually implemented in a BeforeSuite function, and it consists of two steps:

• Defining an E2E config file
• Creating the management cluster and installing providers

Defining an E2E config file

The E2E config file provides a convenient and flexible way to define common tasks for setting up a management cluster.

Using the config file it is possible to:

• Define the list of providers to be installed in the management cluster. Most notably, for each provider it is possible to define:
  • One or more versions of the providers manifest (built from the sources, or pulled from a remote location).
  • A list of additional files to be added to the provider repository, to be used e.g. to provide cluster-templates.yaml files.
• Define the list of variables to be used when doing clusterctl init or clusterctl config cluster.
• Define a list of intervals to be used in the test specs for defining timeouts for the wait and Eventually methods.
• Define the list of images to be loaded in the management cluster (this is specif of management cluster based on kind).

An example E2E config file can be found here.

Creating the management cluster and installing providers

In order to run Cluster API E2E tests, you need a Kubernetes cluster; the NewKindClusterProvider gives you a type that can be used to create a local kind cluster and pre-load images into it, but also existing clusters can be used if available.

Once you have a Kubernetes cluster, the InitManagementClusterAndWatchControllerLogs method provides a convenient way for installing providers.

This method:

• Runs clusterctl init using the above local repository.
• Waits for the providers controllers to be running.
• Creates log watchers for all the providers

Writing test specs

A typical test spec is a sequence of:

• Creating a namespace to host in isolation all the test objects
• Creating objects in the management cluster, wait for the corresponding infrastructure to be provisioned.
• Exec operations like e.g. changing the Kubernetes version or clusterctl move, wait for the action to complete.
• Delete objects in the management cluster, wait for the corresponding infrastructure to be terminated.

Creating Namespaces

The CreateNamespaceAndWatchEvents method provides a convenient way to create a namespace and setup watches for capturing namespaces events

Creating objects

There are two possible approaches for creating objects in the management cluster:

• Create object by object: create the Cluster object, then AwsCluster, Machines, AwsMachines etc.
• Apply a cluster-templates.yaml file thus creating all the objects this file contains.

The first approaches leverage on the controller-runtime Client and gives you full control, but it comes with some drawbacks as well, because this method does not reflect directly real user workflows, and most importantly, the resulting tests are not as reusable with other infrastructure providers. (See writing portable tests).

We recommend using the ClusterTemplate method and the Apply method for creating objects in the cluster. This methods mimics the recommended user workflows, and it is based on cluster-templates.yaml files that can be provided via the E2E config file, and thus easily swappable when changing the target infrastructure provider.

After creating objects in the cluster, use the existing methods in the Cluster API test framework to discover which object was created in the cluster so your code can adapt to different cluster-templates.yaml files.

Once you have objects references, the framework includes methods for waiting for the corresponding infrastructure to be provisioned, e.g. WaitForClusterToProvision, WaitForKubeadmControlPlaneMachinesToExist.

Exec operations

You can use Cluster API test framework methods to modify Cluster API objects, as a last option, use the controller-runtime Client.

The Cluster API test framework includes also methods for executing clusterctl operations, like e.g. the ClusterTemplate method, the ClusterctlMove method etc.; in order to improve observability, each clusterctl operation creates a detailed log.

After using clusterctl operations, you can rely on the Get and on the Wait methods defined in the Cluster API test framework to check if the operation completed successfully.

Tear down

After a test completes/fails, it is required to:

• Collect all the logs for the Cluster API controllers
• Dump all the relevant Cluster API/Kubernetes objects
• Cleanup all the infrastructure resources created during the test

Those task are usually implemented in the AfterSuite, and again the Cluster API test framework provides you useful methods for those tasks.

Please note that despite the fact that test specs are expected to delete objects in the management cluster and wait for the corresponding infrastructure to be terminated, it can happen that the test spec fails before starting object deletion or that objects deletion itself fails.

As a consequence, when scheduling/running a test suite, it is required to ensure all the generated resources are cleaned up. In Kubernetes, this is implemented by the boskos project.

Writing portable E2E tests

A portable E2E test is a test can run with different infrastructure providers by simply changing the test configuration file.

Following recommendations should be followed to write portable E2E tests:

• Create different E2E config file, one for each target infrastructure provider, providing different sets of env variables and timeout intervals.
• Use the [InitManagementCluster method] for setting up the management cluster.
• Use the ClusterTemplate method and the Apply method for creating objects in the cluster using cluster-templates.yaml files instead of hard coding object creation.
• Use the Get methods defined in the Cluster API test framework to checks object being created, so your code can adapt to different cluster-templates.yaml files.
• Never hard code the infrastructure provider name in your test spec. Instead, use the InfrastructureProvider method to get access to the name of the infrastructure provider defined in the E2E config file.
• Never hard code wait intervals in your test spec. Instead use the GetIntervals method to get access to the intervals defined in the E2E config file.

Cluster API conformance tests

As of today there is no a well-defined suites of E2E tests that can be used as a baseline for Cluster API conformance.

However, creating such suite is something that can provide a huge value for the long term success of the project.

The test E2E package provide examples of how this can be achieved implemeting a set of and reusable test specs for the most common Cluster API use cases.

Controllers

This page is still being written - stay tuned!

Bootstrap Controller

Bootstrapping is the process in which:

1. A cluster is bootstrapped
2. A machine is bootstrapped and takes on a role within a cluster

CABPK is the reference bootstrap provider and is based on kubeadm. CABPK codifies the steps for creating a cluster in multiple configurations.

See proposal for the full details on how the bootstrap process works.

Implementations

• Kubeadm (Reference Implementation)

Cluster Controller

The Cluster controller’s main responsibilities are:

• Setting an OwnerReference on the infrastructure object referenced in Cluster.Spec.InfrastructureRef.
• Cleanup of all owned objects so that nothing is dangling after deletion.
• Keeping the Cluster’s status in sync with the infrastructure Cluster’s status.
• Creating a kubeconfig secret for workload clusters.

Contracts

Infrastructure Provider

The general expectation of an infrastructure provider is to provision the necessary infrastructure components needed to run a Kubernetes cluster. As an example, the AWS infrastructure provider, specifically the AWSCluster reconciler, will provision a VPC, some security groups, an ELB, a bastion instance and some other components all with AWS best practices baked in. Once that infrastructure is provisioned and ready to be used the AWSMachine reconciler takes over and provisions EC2 instances that will become a Kubernetes cluster through some bootstrap mechanism.

Required status fields

The InfrastructureCluster object must have a status object.

The spec object must have the following fields defined:

• controlPlaneEndpoint - identifies the endpoint used to connect to the target’s cluster apiserver.

The status object must have the following fields defined:

• ready - a boolean field that is true when the infrastructure is ready to be used.

Optional status fields

The status object may define several fields that do not affect functionality if missing:

• failureReason - is a string that explains why a fatal error has occurred, if possible.
• failureMessage - is a string that holds the message contained by the error.

Example:

kind: MyProviderCluster
apiVersion: infrastructure.cluster.x-k8s.io/v1alpha3
spec:
  controlPlaneEndpoint:
    host: example.com
    port: 6443
status:
    ready: true

Secrets

If you are using the kubeadm bootstrap provider you do not have to provide Cluster API any secrets. It will generate all necessary CAs (certificate authorities) for you.

However, if you provide a CA for the cluster then Cluster API will be able to generate a kubeconfig secret. This is useful if you have a custom CA for or do not want to use the bootstrap provider’s generated self-signed CA.

Alternatively can entirely bypass Cluster API generating a kubeconfig entirely if you provide a kubeconfig secret formatted as described below.

Machine Controller

The Machine controller’s main responsibilities are:

• Setting an OwnerReference on:
  • Each Machine object to the Cluster object.
  • The associated BootstrapConfig object.
  • The associated InfrastructureMachine object.
• Copy data from BootstrapConfig.Status.BootstrapData to Machine.Spec.Bootstrap.Data if Machine.Spec.Bootstrap.Data is empty.
• Setting NodeRefs to be able to associate machines and kubernetes nodes.
• Deleting Nodes in the target cluster when the associated machine is deleted.
• Cleanup of related objects.
• Keeping the Machine’s Status object up to date with the InfrastructureMachine’s Status object.
• Finding Kubernetes nodes matching the expected providerID in the workload cluster.

After the machine controller sets the OwnerReferences on the associated objects, it waits for the bootstrap and infrastructure objects referenced by the machine to have the Status.Ready field set to true. When the infrastructure object is ready, the machine controller will attempt to read its Spec.ProviderID and copy it into Machine.Spec.ProviderID.

The machine controller uses the kubeconfig for the new workload cluster to watch new nodes coming up. When a node appears with Node.Spec.ProviderID matching Machine.Spec.ProviderID, the machine controller transitions the associated machine into the Provisioned state. When the infrastructure ref is also
Ready, the machine controller marks the machine as Running.

Contracts

Cluster API

Cluster associations are made via labels.

Expected labels

Bootstrap provider

The BootstrapConfig object must have a status object.

To override the bootstrap provider, a user (or external system) can directly set the Machine.Spec.Bootstrap.Data field. This will mark the machine as ready for bootstrapping and no bootstrap data will be copied from the BootstrapConfig object.

Required status fields

The status object must have several fields defined:

• ready - a boolean field indicating the bootstrap config data is generated and ready for use.
• dataSecretName - a string field referencing the name of the secret that stores the generated bootstrap data.

Optional status fields

The status object may define several fields that do not affect functionality if missing:

• failureReason - a string field explaining why a fatal error has occurred, if possible.
• failureMessage - a string field that holds the message contained by the error.

Example:

kind: MyBootstrapProviderConfig
apiVersion: bootstrap.cluster.x-k8s.io/v1alpha3
status:
    ready: true
    dataSecretName: "MyBootstrapSecret"

Infrastructure provider

The InfrastructureMachine object must have both spec and status objects.

Required spec fields

The spec object must at least one field defined:

• providerID - a cloud provider ID identifying the machine.

Required status fields

The status object must at least one field defined:

• ready - a boolean field indicating if the infrastructure is ready to be used or not.

Optional status fields

The status object may define several fields that do not affect functionality if missing:

• failureReason - is a string that explains why a fatal error has occurred, if possible.
• failureMessage - is a string that holds the message contained by the error.

Example:

kind: MyMachine
apiVersion: infrastructure.cluster.x-k8s.io/v1alpha3
spec:
    providerID: cloud:////my-cloud-provider-id
status:
    ready: true

Secrets

The Machine controller will create a secret or use an existing secret in the following format:

MachineSet

A MachineSet is an immutable abstraction over Machines.

Its main responsibilities are:

• Adopting unowned Machines that aren’t assigned to a MachineSet
• Adopting unmanaged Machines that aren’t assigned a Cluster
• Booting a group of N machines
  • Monitor the status of those booted machines

MachineDeployment

A MachineDeployment orchestrates deployments over a fleet of MachineSets.

Its main responsibilities are:

• Adopting matching MachineSets not assigned to a MachineDeployment
• Adopting matching MachineSets not assigned to a Cluster
• Managing the Machine deployment process
  • Scaling up new MachineSets when changes are made
  • Scaling down old MachineSets when newer MachineSets replace them
• Updating the status of MachineDeployment objects

MachineHealthCheck

A MachineHealthCheck is responsible for remediating unhealthy Machines.

Its main responsibilities are:

• Checking the health of Nodes in the workload clusters against a list of unhealthy conditions
• Remediating Machine’s for Nodes determined to be unhealthy

Control Plane Controller

The Control Plane controller’s main responsibilities are:

• Managing a set of machines that represent a Kubernetes control plane.
• Provide information about the state of the control plane to downstream consumers.
• Create/manage a secret with the kubeconfig file for accessing the workload cluster.

A reference implementation is managed within the core Cluster API project as the Kubeadm control plane controller (KubeadmControlPlane). In this document, we refer to an example ImplementationControlPlane where not otherwise specified.

Contracts

Control Plane Provider

The general expectation of a control plane controller is to instantiate a Kubernetes control plane consisting of the following services:

Required Control Plane Services

• etcd
• Kubernetes API Server
• Kubernetes Controller Manager
• Kubernetes Scheduler

Optional Control Plane Services

• Cloud controller manager
• Cluster DNS (e.g. CoreDNS)
• Service proxy (e.g. kube-proxy)

Prohibited Services

• CNI - should be left to user to apply once control plane is instantiated.

Relationship to other Cluster API types

The ImplementationControlPlane must rely on the existence of status.controlplaneEndpoint in its parent Cluster object.

CRD contracts

Required spec fields for implementations using replicas

• replicas - is an integer representing the number of desired replicas. In the KubeadmControlPlane, this represents the desired number of desired control plane machines.

• scale subresource with the following signature:

scale:
  labelSelectorPath: .status.selector
  specReplicasPath: .spec.replicas
  statusReplicasPath: .status.replicas
status: {}

More information about the scale subresource can be found in the Kubernetes documentation.

Required status fields

The ImplementationControlPlane object must have a status object.

The status object must have the following fields defined:

Required status fields for implementations using replicas

Where the ImplementationControlPlane has a concept of replicas, e.g. most high availability control planes, then the status object must have the following fields defined:

Optional status fields

The status object may define several fields:

• failureReason - is a string that explains why an error has occurred, if possible.
• failureMessage - is a string that holds the message contained by the error.
• externalManagedControlPlane - is a bool that should be set to true if the Node objects do not exist in the cluster. For example, managed control plane providers for AKS, EKS, GKE, etc, should set this to true. Leaving the field undefined is equivalent to setting the value to false.

Example usage

kind: KubeadmControlPlane
apiVersion: cluster.x-k8s.io/v1alpha3
metadata:
  name: kcp-1
  namespace: default
spec:
  infrastructureTemplate:
    name: kcp-infra-template
    namespace: default
  kubeadmConfigSpec:
    clusterConfiguration:
  version: v1.16.2

Kubeconfig management

Control Plane providers are expected to create and maintain a Kubeconfig secret for operators to gain initial access to the cluster. If a provider uses client certificates for authentication in these Kubeconfigs, the client certificate should be kept with a reasonably short expiration period and periodically regenerated to keep a valid set of credentials available. As an example, the Kubeadm Control Plane provider uses a year of validity and refreshes the certificate after 6 months.

Provider Implementers

Cluster API v1alpha1 compared to v1alpha2

Providers

v1alpha1

Providers in v1alpha1 wrap behavior specific to an environment to create the infrastructure and bootstrap instances into Kubernetes nodes. Examples of environments that have integrated with Cluster API v1alpha1 include, AWS, GCP, OpenStack, Azure, vSphere and others. The provider vendors in Cluster API’s controllers, registers its own actuators with the Cluster API controllers and runs a single manager to complete a Cluster API management cluster.

v1alpha2

v1alpha2 introduces two new providers and changes how the Cluster API is consumed. This means that in order to have a complete management cluster that is ready to build clusters you will need three managers.

• Core (Cluster API)
• Bootstrap (kubeadm)
• Infrastructure (aws, gcp, azure, vsphere, etc)

Cluster API’s controllers are no longer vendored by providers. Instead, Cluster API offers its own independent controllers that are responsible for the core types:

• Cluster
• Machine
• MachineSet
• MachineDeployment

Bootstrap providers are an entirely new concept aimed at reducing the amount of kubeadm boilerplate that every provider reimplemented in v1alpha1. The Bootstrap provider is responsible for running a controller that generates data necessary to bootstrap an instance into a Kubernetes node (cloud-init, bash, etc).

v1alpha1 “providers” have become Infrastructure providers. The Infrastructure provider is responsible for generating actual infrastructure (networking, load balancers, instances, etc) for a particular environment that can consume bootstrap data to turn the infrastructure into a Kubernetes cluster.

Actuators

v1alpha1

Actuators are interfaces that the Cluster API controller calls. A provider pulls in the generic Cluster API controller and then registers actuators to run specific infrastructure logic (calls to the provider cloud).

v1alpha2

Actuators are not used in this version. Cluster API’s controllers are no longer shared across providers and therefore they do not need to know about the actuator interface. Instead, providers communicate to each other via Cluster API’s central objects, namely Machine and Cluster. When a user modifies a Machine with a reference, each provider will notice that update and respond in some way. For example, the Bootstrap provider may attach BootstrapData to a BootstrapConfig which will then be attached to the Machine object via Cluster API’s controllers or the Infrastructure provider may create a cloud instance for Kubernetes to run on.

clusterctl

v1alpha1

clusterctl was a command line tool packaged with v1alpha1 providers. The goal of this tool was to go from nothing to a running management cluster in whatever environment the provider was built for. For example, Cluster-API-Provider-AWS packaged a clusterctl that created a Kubernetes cluster in EC2 and installed the necessary controllers to respond to Cluster API’s APIs.

v1alpha2

clusterctl is likely becoming provider-agnostic meaning one clusterctl is bundled with Cluster API and can be reused across providers. Work here is still being figured out but providers will not be packaging their own clusterctl anymore.

Cluster API v1alpha2 compared to v1alpha3

Minimum Go version

• The Go version used by Cluster API is now Go 1.13+

In-Tree bootstrap provider

• Cluster API now ships with the Kubeadm Bootstrap provider (CABPK).
• Update import paths from sigs.k8s.io/cluster-api-bootstrap-provider-kubeadm to sigs.k8s.io/cluster-api/bootstrap/kubeadm.

Machine spec.metadata field has been removed

• The field has been unused for quite some time and didn’t have any function.
• If you have been using this field to setup MachineSet or MachineDeployment, switch to MachineTemplate’s metadata instead.

Set spec.clusterName on Machine, MachineSet, MachineDeployments

• The field is now required on all Cluster dependant objects.
• The cluster.x-k8s.io/cluster-name label is created automatically by each respective controller.

Context is now required for external.CloneTemplate function.

• Pass a context as the first argument to calls to external.CloneTemplate.

Context is now required for external.Get function.

• Pass a context as the first argument to calls to external.Get.

Cluster and Machine Status.Phase field values now start with an uppercase letter

• To be consistent with Pod phases in k/k.
• More details in https://github.com/kubernetes-sigs/cluster-api/pull/1532/files.

MachineClusterLabelName is renamed to ClusterLabelName

• The variable name is renamed as this label isn’t applied only to machines anymore.
• This label is also applied to external objects(bootstrap provider, infrastructure provider)

Cluster and Machine controllers now set cluster.x-k8s.io/cluster-name to external objects.

• In addition to the OwnerReference back to the Cluster, a label is now added as well to any external objects, for example objects such as KubeadmConfig (bootstrap provider), AWSCluster (infrastructure provider), AWSMachine (infrastructure provider), etc.

The util/restmapper package has been removed

• Controller runtime has native support for a DynamicRESTMapper, which is used by default when creating a new Manager.

Generated kubeconfig admin username changed from kubernetes-admin to <cluster-name>-admin

• The kubeconfig secret shipped with Cluster API now uses the cluster name as prefix to the username field.

Changes to sigs.k8s.io/cluster-api/controllers/remote

• The ClusterClient interface has been removed.
• remote.NewClusterClient now returns a sigs.k8s.io/controller-runtime/pkg/client Client. It also requires client.ObjectKey instead of a cluster reference. The signature changed:
  • From: func NewClusterClient(c client.Client, cluster *clusterv1.Cluster) (ClusterClient, error)
  • To: func NewClusterClient(c client.Client, cluster client.ObjectKey, scheme runtime.Scheme) (client.Client, error)
• Same for the remote client ClusterClientGetter interface:
  • From: type ClusterClientGetter func(ctx context.Context, c client.Client, cluster *clusterv1.Cluster, scheme *runtime.Scheme) (client.Client, error)
  • To: type ClusterClientGetter func(ctx context.Context, c client.Client, cluster client.ObjectKey, scheme *runtime.Scheme) (client.Client, error)
• remote.RESTConfig now uses client.ObjectKey instead of a cluster reference. Signature change:
  • From: func RESTConfig(ctx context.Context, c client.Client, cluster *clusterv1.Cluster) (*restclient.Config, error)
  • To: func RESTConfig(ctx context.Context, c client.Client, cluster client.ObjectKey) (*restclient.Config, error)

Related changes to sigs.k8s.io/cluster-api/util

• A helper function util.ObjectKey could be used to get client.ObjectKey for a Cluster, Machine etc.
• The returned client is no longer configured for lazy discovery. Any consumers that attempt to create a client prior to the server being available will now see an error.
• Getter for a kubeconfig secret, associated with a cluster requires client.ObjectKey instead of a cluster reference. Signature change:
  • From: func Get(ctx context.Context, c client.Client, cluster client.ObjectKey, purpose Purpose) (*corev1.Secret, error)
  • To: func Get(ctx context.Context, c client.Client, cluster *clusterv1.Cluster, purpose Purpose) (*corev1.Secret, error)

A Machine is now considered a control plane if it has cluster.x-k8s.io/control-plane set, regardless of value

• Previously examples and tests were setting/checking for the label to be set to true.
• The function util.IsControlPlaneMachine was previously checking for any value other than empty string, while now we only check if the associated label exists.

Machine Status.Phase field set to Provisioned if a NodeRef is set but infrastructure is not ready

• The machine Status.Phase is set back to Provisioned if the infrastructure is not ready. This is only applicable if the infrastructure node status does not have any errors set.

Cluster Status.Phase transition to Provisioned additionally needs at least one APIEndpoint to be available.

• Previously, the sole requirement to transition a Cluster’s Status.Phase to Provisioned was a true value of Status.InfrastructureReady. Now, there are two requirements: a true value of Status.InfrastructureReady and at least one entry in Status.APIEndpoints.
• See https://github.com/kubernetes-sigs/cluster-api/pull/1721/files.

Status.ErrorReason and Status.ErrorMessage fields, populated to signal a fatal error has occurred, have been renamed in Cluster, Machine and MachineSet

• Status.ErrorReason has been renamed to Status.FailureReason
• Status.ErrorMessage has been renamed to Status.FailureMessage

The external.ErrorsFrom function has been renamed to external.FailuresFrom

• The function has been modified to reflect the rename of Status.ErrorReason to Status.FailureReason and Status.ErrorMessage to Status.FailureMessage.

External objects will need to rename Status.ErrorReason and Status.ErrorMessage

• As a follow up to the changes mentioned above - for the external.FailuresFrom function to retain its functionality, external objects (e.g., AWSCluster, AWSMachine, etc.) will need to rename the fields as well.
• Status.ErrorReason should be renamed to Status.FailureReason
• Status.ErrorMessage should be renamed to Status.FailureMessage

The field Cluster.Status.APIEndpoints is removed in favor of Cluster.Spec.ControlPlaneEndpoint

• The slice in Cluster.Status has been removed and replaced by a single APIEndpoint field under Spec.
• Infrastructure providers MUST expose a ControlPlaneEndpoint field in their cluster infrastructure resource at Spec.ControlPlaneEndpoint. They may optionally remove the Status.APIEndpoints field (Cluster API no longer uses it).

Data generated from a bootstrap provider is now stored in a secret.

• The Cluster API Machine Controller no longer reconciles the bootstrap provider status.bootstrapData field, but instead looks at status.dataSecretName.
• The Machine.Spec.Bootstrap.Data field is deprecated and will be removed in a future version.
• Bootstrap providers must create a Secret in the bootstrap resource’s namespace and store the name in the bootstrap resource’s status.dataSecretName field.
  • The secret created by the bootstrap provider is of type cluster.x-k8s.io/secret.
  • On reconciliation, we suggest to migrate from the deprecated field to a secret reference.
• Infrastructure providers must look for the bootstrap data secret name in Machine.Spec.Bootstrap.DataSecretName and fallback to Machine.Spec.Bootstrap.Data.

The cloudinit module under the Kubeadm bootstrap provider has been made private

The cloudinit module has been moved to an internal directory as it is not designed to be a public interface consumed outside of the existing module.

Interface for Bootstrap Provider Consumers

• Consumers of bootstrap configuration, Machine and eventually MachinePool, must adhere to a contract that defines a set of required fields used for coordination with the kubeadm bootstrap provider.
  • apiVersion to check for supported version/kind.
  • kind to check for supported version/kind.
  • metadata.labels["cluster.x-k8s.io/control-plane"] only present in the case of a control plane Machine.
  • spec.clusterName to retrieve the owning Cluster status.
  • spec.bootstrap.dataSecretName to know where to put bootstrap data with sensitive information. Consumers must also verify the secret type matches cluster.x-k8s.io/secret.
  • status.infrastuctureReady to understand the state of the configuration consumer so the bootstrap provider can take appropriate action (e.g. renew bootstrap token).

Support the cluster.x-k8s.io/paused annotation and Cluster.Spec.Paused field.

• A new annotation cluster.x-k8s.io/paused provides the ability to pause reconciliation on specific objects.
• A new field Cluster.Spec.Paused provides the ability to pause reconciliation on a Cluster and all associated objects.
• A helper function util.IsPaused can be used on any Kubernetes object associated with a Cluster and can be used during a Reconcile loop:

  // Return early if the object or Cluster is paused.
  if util.IsPaused(cluster, <object>) {
    logger.Info("Reconciliation is paused for this object")
    return ctrl.Result{}, nil
  }
  

• Unless your controller is already watching Clusters, add a Watch to get notifications when Cluster.Spec.Paused field changes. In most cases, predicates.ClusterUnpaused and util.ClusterToObjectsMapper can be used like in the example below:

  // Add a watch on clusterv1.Cluster object for paused notifications.
  clusterToObjectFunc, err := util.ClusterToObjectsMapper(mgr.GetClient(), <List object here>, mgr.GetScheme())
  if err != nil {
    return err
  }
  err = controller.Watch(
      &source.Kind{Type: &cluserv1.Cluster{}},
      &handler.EnqueueRequestsFromMapFunc{
          ToRequests: clusterToObjectFunc,
      },
      predicates.ClusterUnpaused(r.Log),
  )
  if err != nil {
    return err
  }
  

  NB: You need to have cluster.x-k8s.io/cluster-name applied to all your objects for the mapper to function.
• In some cases, you’ll want to not just watch on Cluster.Spec.Paused changes, but also on Cluster.Status.InfrastructureReady. For those cases predicates.ClusterUnpausedAndInfrastructureReady should be used instead.

  // Add a watch on clusterv1.Cluster object for paused and infrastructureReady notifications.
  clusterToObjectFunc, err := util.ClusterToObjectsMapper(mgr.GetClient(), <List object here>, mgr.GetScheme())
  if err != nil {
    return err
  }
  err = controller.Watch(
        &source.Kind{Type: &cluserv1.Cluster{}},
        &handler.EnqueueRequestsFromMapFunc{
            ToRequests: clusterToObjectFunc,
        },
        predicates.ClusterUnpausedAndInfrastructureReady(r.Log),
    )
    if err != nil {
      return err
    }
  

[OPTIONAL] Support failure domains.

An infrastructure provider may or may not implement the failure domains feature. Failure domains gives Cluster API just enough information to spread machines out reducing the risk of a target cluster failing due to a domain outage. This is particularly useful for Control Plane providers. They are now able to put control plane nodes in different domains.

An infrastructure provider can implement this by setting the InfraCluster.Status.FailureDomains field with a map of unique keys to failureDomainSpecs as well as respecting a set Machine.Spec.FailureDomain field when creating instances.

To support migration from failure domains that were previously specified through provider-specific resources, the Machine controller will support updating Machine.Spec.FailureDomain field if Spec.FailureDomain is present and defined on the provider-defined infrastructure resource.

Please see the cluster and machine infrastructure provider specifications for more detail.

Refactor kustomize config/ folder to support multi-tenancy when using webhooks.

Pre-Requisites: Upgrade to CRD v1.

More details and background can be found in Issue #2275 and PR #2279.

Goals:

• Have all webhook related components in the capi-webhook-system namespace.
  • Achieves multi-tenancy and guarantees that both CRD and webhook resources can live globally and can be patched in future iterations.
• Run a new manager instance that ONLY runs webhooks and doesn’t install any reconcilers.

Steps:

• In config/certmanager/

  • Patch
    • certificate.yaml: The secretName value MUST be set to $(SERVICE_NAME)-cert.
    • kustomization.yaml: Add the following to varReference

      - kind: Certificate
        group: cert-manager.io
        path: spec/secretName
      

• In config/

  • Create
    • kustomization.yaml: This file is going to function as the new entrypoint to run kustomize build. PROVIDER_NAME is the name of your provider, e.g. aws. PROVIDER_TYPE is the type of your provider, e.g. control-plane, bootstrap, infrastructure.

      namePrefix: {{e.g. capa-, capi-, etc.}}
      
      commonLabels:
        cluster.x-k8s.io/provider: "{{PROVIDER_TYPE}}-{{PROVIDER_NAME}}"
      
      bases:
      - crd
      - webhook # Disable this if you're not using the webhook functionality.
      - default
      
      patchesJson6902:
      - target: # NOTE: This patch needs to be repeatd for EACH CustomResourceDefinition you have under crd/bases.
          group: apiextensions.k8s.io
          version: v1
          kind: CustomResourceDefinition
          name: {{CRD_NAME_HERE}}
        path: patch_crd_webhook_namespace.yaml
      

    • patch_crd_webhook_namespace.yaml: This patch sets the conversion webhook namespace to capi-webhook-system.

      - op: replace
        path: "/spec/conversion/webhook/clientConfig/service/namespace"
        value: capi-webhook-system
      

• In config/default

  • Create
    • namespace.yaml

      apiVersion: v1
      kind: Namespace
      metadata:
        name: system
      

  • Move
    • manager_image_patch.yaml to config/manager
    • manager_label_patch.yaml to config/manager
    • manager_pull_policy.yaml to config/manager
    • manager_auth_proxy_patch.yaml to config/manager
    • manager_webhook_patch.yaml to config/webhook
    • webhookcainjection_patch.yaml to config/webhook
    • manager_label_patch.yaml to trash.
  • Patch
    • kustomization.yaml
      • Add under resources:

        resources:
        - namespace.yaml
        

      • Replace bases with:

        bases:
        - ../rbac
        - ../manager
        

      • Add under patchesStrategicMerge:

        patchesStrategicMerge:
        - manager_role_aggregation_patch.yaml
        

      • Remove ../crd from bases (now in config/kustomization.yaml).
      • Remove namePrefix (now in config/kustomization.yaml).
      • Remove commonLabels (now in config/kustomization.yaml).
      • Remove from patchesStrategicMerge:
        • manager_image_patch.yaml
        • manager_pull_policy.yaml
        • manager_auth_proxy_patch.yaml
        • manager_webhook_patch.yaml
        • webhookcainjection_patch.yaml
        • manager_label_patch.yaml
      • Remove from vars:
        • CERTIFICATE_NAMESPACE
        • CERTIFICATE_NAME
        • SERVICE_NAMESPACE
        • SERVICE_NAME

• In config/manager

  • Patch
    • manager.yaml: Remove the Namespace object.
    • kustomization.yaml:
      • Add under patchesStrategicMerge:

        patchesStrategicMerge:
        - manager_image_patch.yaml
        - manager_pull_policy.yaml
        - manager_auth_proxy_patch.yaml
        

• In config/webhook

  • Patch
    • kustomizeconfig.yaml
      • Add the following to varReference

        - kind: Deployment
          path: spec/template/spec/volumes/secret/secretName
        

    • kustomization.yaml
      • Add namespace: capi-webhook-system at the top of the file.
      • Under resources, add ../certmanager and ../manager.
      • Add at the bottom of the file:

        patchesStrategicMerge:
        - manager_webhook_patch.yaml
        - webhookcainjection_patch.yaml # Disable this value if you don't have any defaulting or validation webhook. If you don't know, you can check if the manifests.yaml file in the same directory has any contents.
        
        vars:
        - name: CERTIFICATE_NAMESPACE # namespace of the certificate CR
          objref:
            kind: Certificate
            group: cert-manager.io
            version: v1alpha2
            name: serving-cert # this name should match the one in certificate.yaml
          fieldref:
            fieldpath: metadata.namespace
        - name: CERTIFICATE_NAME
          objref:
            kind: Certificate
            group: cert-manager.io
            version: v1alpha2
            name: serving-cert # this name should match the one in certificate.yaml
        - name: SERVICE_NAMESPACE # namespace of the service
          objref:
            kind: Service
            version: v1
            name: webhook-service
          fieldref:
            fieldpath: metadata.namespace
        - name: SERVICE_NAME
          objref:
            kind: Service
            version: v1
            name: webhook-service
        

    • manager_webhook_patch.yaml
      • Under containers find manager and add after name

        - "--metrics-addr=127.0.0.1:8080"
        - "--webhook-port=9443"
        

      • Under volumes find cert and replace secretName‘s value with $(SERVICE_NAME)-cert.
    • service.yaml
      • Remove the selector map, if any. The control-plane label is not needed anymore, a unique label is applied using commonLabels under config/kustomization.yaml.

In main.go

• Default the webhook-port flag to 0

  flag.IntVar(&webhookPort, "webhook-port", 0,
  	"Webhook Server port, disabled by default. When enabled, the manager will only work as webhook server, no reconcilers are installed.")
  

• The controller MUST register reconcilers if and only if webhookPort == 0.
• The controller MUST register webhooks if and only if webhookPort != 0.

After all the changes above are performed, kustomize build MUST target config/, rather than config/default. Using your favorite editor, search for config/default in your repository and change the paths accordingly.

In addition, often the Makefile contains a sed-replacement for manager_image_patch.yaml, this file has been moved from config/default to config/manager. Using your favorite editor, search for manager_image_patch in your repository and change the paths accordingly.

Apply the contract version label cluster.x-k8s.io/<version>: version1_version2_version3 to your CRDs

• Providers MUST set cluster.x-k8s.io/<version> labels on all Custom Resource Definitions related to Cluster API starting with v1alpha3.
• The label is a map from an API Version of Cluster API (contract) to your Custom Resource Definition versions.
  • The value is a underscore-delimited (_) list of versions.
  • Each value MUST point to an available version in your CRD Spec.
• The label allows Cluster API controllers to perform automatic conversions for object references, the controllers will pick the last available version in the list if multiple versions are found.
• To apply the label to CRDs it’s possible to use commonLabels in your kustomize.yaml file, usually in config/crd.

In this example we show how to map a particular Cluster API contract version to your own CRD using Kustomize’s commonLabels feature:

commonLabels:
  cluster.x-k8s.io/v1alpha2: v1alpha1
  cluster.x-k8s.io/v1alpha3: v1alpha2
  cluster.x-k8s.io/v1beta1: v1alphaX_v1beta1

Upgrade to CRD v1

• Providers should upgrade their CRDs to v1
• Minimum Kubernetes version supporting CRDv1 is v1.16
• In Makefile target generate-manifests:, add the following property to the crd crdVersions=v1

generate-manifests: $(CONTROLLER_GEN) ## Generate manifests e.g. CRD, RBAC etc.
  $(CONTROLLER_GEN) \
    paths=./api/... \
    crd:crdVersions=v1 \
    output:crd:dir=$(CRD_ROOT) \
    output:webhook:dir=$(WEBHOOK_ROOT) \
    webhook
  $(CONTROLLER_GEN) \
    paths=./controllers/... \
    output:rbac:dir=$(RBAC_ROOT) \
    rbac:roleName=manager-role

• For all the CRDs in the config/crd/bases change the version of CustomResourceDefinition to v1

apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition

to

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition

• In the config/crd/kustomizeconfig.yaml file, change the path of the webhook

path: spec/conversion/webhookClientConfig/service/name

to

spec/conversion/webhook/clientConfig/service/name

• Make the same change of changing v1beta to v1 version in the config/crd/patches
• In the config/crd/patches/webhook_in_******.yaml file, add the conversionReviewVersions property to the CRD

apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  ...
spec:
  conversion:
    strategy: Webhook
    webhookClientConfig:
    ...

to

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  ...
spec:
  strategy: Webhook
  webhook:
  conversionReviewVersions: ["v1", "v1beta1"]
  clientConfig:
  ...

Add matchPolicy=Equivalent kubebuilder marker in webhooks

• All providers should set “matchPolicy=Equivalent” kubebuilder marker for webhooks on all Custom Resource Definitions related to Cluster API starting with v1alpha3.
• Specifying Equivalent ensures that webhooks continue to intercept the resources they expect when upgrades enable new versions of the resource in the API server.
• E.g., matchPolicy is added to AWSMachine (/api/v1alpha3/awsmachine_webhook.go)

  // +kubebuilder:webhook:verbs=create;update,path=/validate-infrastructure-cluster-x-k8s-io-v1alpha3-awsmachine,mutating=false,failurePolicy=fail,matchPolicy=Equivalent,groups=infrastructure.cluster.x-k8s.io,resources=awsmachines,versions=v1alpha3,name=validation.awsmachine.infrastructure.cluster.x-k8s.io
  

• Support for matchPolicy marker has been added in kubernetes-sigs/controller-tools. Providers needs to update controller-tools dependency to make use of it, usually in hack/tools/go.mod.

[OPTIONAL] Implement --feature-gates flag in main.go

• Cluster API now ships with a new experimental package that lives under exp/ containing both API types and controllers.
• Controller and types should always live behind a gate defined under the feature/ package.
• If you’re planning to support experimental features or API types in your provider or codebase, you can add feature.MutableGates.AddFlag(fs) to your main.go when initializing command line flags. For a full example, you can refer to the main.go in Cluster API or under bootstrap/kubeadm/.

NOTE: To enable experimental features users are required to set the same --feature-gates flag across providers. For example, if you want to enable MachinePool, you’ll have to enable in both Cluster API deployment and the Kubeadm Bootstrap Provider. In the future, we’ll revisit this user experience and provide a centralized way to configure gates across all Cluster API (inc. providers) controllers.

clusterctl

clusterctl is now bundled with Cluster API, provider-agnostic and can be reused across providers. It is the recommended way to setup a management cluster and it implements best practices to avoid common mis-configurations and for managing the life-cycle of deployed providers, e.g. upgrades.

see clusterctl provider contract for more details.

Cluster Infrastructure Provider Specification

Overview

A cluster infrastructure provider supplies whatever prerequisites are necessary for running machines. Examples might include networking, load balancers, firewall rules, and so on.

Data Types

A cluster infrastructure provider must define an API type for “infrastructure cluster” resources. The type:

1. Must belong to an API group served by the Kubernetes apiserver
2. May be implemented as a CustomResourceDefinition, or as part of an aggregated apiserver
3. Must be namespace-scoped
4. Must have the standard Kubernetes “type metadata” and “object metadata”
5. Must have a spec field with the following:
   1. Required fields:
      1. controlPlaneEndpoint (apiEndpoint): the endpoint for the cluster’s control plane. apiEndpoint is defined as:
         • host (string): DNS name or IP address
         • port (int32): TCP port
6. Must have a status field with the following:
   1. Required fields:
      1. ready (boolean): indicates the provider-specific infrastructure has been provisioned and is ready
   2. Optional fields:
      1. failureReason (string): indicates there is a fatal problem reconciling the provider’s infrastructure; meant to be suitable for programmatic interpretation
      2. failureMessage (string): indicates there is a fatal problem reconciling the provider’s infrastructure; meant to be a more descriptive value than failureReason
      3. failureDomains (failureDomains): the failure domains that machines should be placed in. failureDomains is a map, defined as map[string]FailureDomainSpec. A unique key must be used for each FailureDomainSpec. FailureDomainSpec is defined as:
         • controlPlane (bool): indicates if failure domain is appropriate for running control plane instances.
         • attributes (map[string]string): arbitrary attributes for users to apply to a failure domain.

Behavior

A cluster infrastructure provider must respond to changes to its “infrastructure cluster” resources. This process is typically called reconciliation. The provider must watch for new, updated, and deleted resources and respond accordingly.

The following diagram shows the typical logic for a cluster infrastructure provider:

Normal resource

1. If the resource does not have a Cluster owner, exit the reconciliation
   1. The Cluster API Cluster reconciler populates this based on the value in the Cluster‘s spec.infrastructureRef field.
2. Add the provider-specific finalizer, if needed
3. Reconcile provider-specific cluster infrastructure
   1. If any errors are encountered, exit the reconciliation
4. If the provider created a load balancer for the control plane, record its hostname or IP in spec.controlPlaneEndpoint
5. Set status.ready to true
6. Set status.failureDomains based on available provider failure domains (optional)
7. Patch the resource to persist changes

Deleted resource

1. If the resource has a Cluster owner
   1. Perform deletion of provider-specific cluster infrastructure
   2. If any errors are encountered, exit the reconciliation
2. Remove the provider-specific finalizer from the resource
3. Patch the resource to persist changes

RBAC

Provider controller

A cluster infrastructure provider must have RBAC permissions for the types it defines. If you are using kubebuilder to generate new API types, these permissions should be configured for you automatically. For example, the AWS provider has the following configuration for its AWSCluster type:

// +kubebuilder:rbac:groups=infrastructure.cluster.x-k8s.io,resources=awsclusters,verbs=get;list;watch;create;update;patch;delete
// +kubebuilder:rbac:groups=infrastructure.cluster.x-k8s.io,resources=awsclusters/status,verbs=get;update;patch

A cluster infrastructure provider may also need RBAC permissions for other types, such as Cluster. If you need read-only access, you can limit the permissions to get, list, and watch. The AWS provider has the following configuration for retrieving Cluster resources:

// +kubebuilder:rbac:groups=cluster.x-k8s.io,resources=clusters;clusters/status,verbs=get;list;watch

Cluster API controllers

The Cluster API controller for Cluster resources is configured with full read/write RBAC permissions for all resources in the infrastructure.cluster.x-k8s.io API group. This group represents all cluster infrastructure providers for SIG Cluster Lifecycle-sponsored provider subprojects. If you are writing a provider not sponsored by the SIG, you must grant full read/write RBAC permissions for the “infrastructure cluster” resource in your API group to the Cluster API manager’s ServiceAccount. ClusterRoles can be granted using the aggregation label cluster.x-k8s.io/aggregate-to-manager: "true". The following is an example ClusterRole for a FooCluster resource:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: capi-foo-clusters
  labels:
    cluster.x-k8s.io/aggregate-to-manager: "true"
rules:
- apiGroups:
  - infrastructure.foo.com
  resources:
  - fooclusters
  verbs:
  - create
  - delete
  - get
  - list
  - patch
  - update
  - watch

Note, the write permissions allow the Cluster controller to set owner references and labels on the “infrastructure cluster” resources; they are not used for general mutations of these resources.

Machine Infrastructure Provider Specification

Overview

A machine infrastructure provider is responsible for managing the lifecycle of provider-specific machine instances. These may be physical or virtual instances, and they represent the infrastructure for Kubernetes nodes.

Data Types

A machine infrastructure provider must define an API type for “infrastructure machine” resources. The type:

1. Must belong to an API group served by the Kubernetes apiserver
2. May be implemented as a CustomResourceDefinition, or as part of an aggregated apiserver
3. Must be namespace-scoped
4. Must have the standard Kubernetes “type metadata” and “object metadata”
5. Must have a spec field with the following:
   1. Required fields:
      1. providerID (string): the identifier for the provider’s machine instance
   2. Optional fields:
      1. failureDomain (string): the string identifier of the failure domain the instance is running in for the purposes of backwards compatibility and migrating to the v1alpha3 FailureDomain support (where FailureDomain is specified in Machine.Spec.FailureDomain). This field is meant to be temporary to aid in migration of data that was previously defined on the provider type and providers will be expected to remove the field in the next version that provides breaking API changes, favoring the value defined on Machine.Spec.FailureDomain instead. If supporting conversions from previous types, the provider will need to support a conversion from the provider-specific field that was previously used to the failureDomain field to support the automated migration path.
6. Must have a status field with the following:
   1. Required fields:
      1. ready (boolean): indicates the provider-specific infrastructure has been provisioned and is ready
   2. Optional fields:
      1. failureReason (string): indicates there is a fatal problem reconciling the provider’s infrastructure; meant to be suitable for programmatic interpretation
      2. failureMessage (string): indicates there is a fatal problem reconciling the provider’s infrastructure; meant to be a more descriptive value than failureReason
      3. addresses (MachineAddress): a list of the host names, external IP addresses, internal IP addresses, external DNS names, and/or internal DNS names for the provider’s machine instance. MachineAddress is defined as: - type (string): one of Hostname, ExternalIP, InternalIP, ExternalDNS, InternalDNS - address (string)

Behavior

A machine infrastructure provider must respond to changes to its “infrastructure machine” resources. This process is typically called reconciliation. The provider must watch for new, updated, and deleted resources and respond accordingly.

The following diagram shows the typical logic for a machine infrastructure provider:

Normal resource

1. If the resource does not have a Machine owner, exit the reconciliation
   1. The Cluster API Machine reconciler populates this based on the value in the Machines‘s spec.infrastructureRef field
2. If the resource has status.failureReason or status.failureMessage set, exit the reconciliation
3. If the Cluster to which this resource belongs cannot be found, exit the reconciliation
4. Add the provider-specific finalizer, if needed
5. If the associated Cluster‘s status.infrastructureReady is false, exit the reconciliation
6. If the associated Machine‘s spec.bootstrap.dataSecretName is nil, exit the reconciliation
7. Reconcile provider-specific machine infrastructure
   1. If any errors are encountered:
      1. If they are terminal failures, set status.failureReason and status.failureMessage
      2. Exit the reconciliation
   2. If this is a control plane machine, register the instance with the provider’s control plane load balancer (optional)
8. Set spec.providerID to the provider-specific identifier for the provider’s machine instance
9. Set status.ready to true
10. Set status.addresses to the provider-specific set of instance addresses (optional)
11. Set spec.failureDomain to the provider-specific failure domain the instance is running in (optional)
12. Patch the resource to persist changes

Deleted resource

1. If the resource has a Machine owner
   1. Perform deletion of provider-specific machine infrastructure
   2. If this is a control plane machine, deregister the instance from the provider’s control plane load balancer (optional)
   3. If any errors are encountered, exit the reconciliation
2. Remove the provider-specific finalizer from the resource
3. Patch the resource to persist changes

RBAC

Provider controller

A machine infrastructure provider must have RBAC permissions for the types it defines. If you are using kubebuilder to generate new API types, these permissions should be configured for you automatically. For example, the AWS provider has the following configuration for its AWSMachine type:

// +kubebuilder:rbac:groups=infrastructure.cluster.x-k8s.io,resources=awsmachines,verbs=get;list;watch;create;update;patch;delete
// +kubebuilder:rbac:groups=infrastructure.cluster.x-k8s.io,resources=awsmachines/status,verbs=get;update;patch

A machine infrastructure provider may also need RBAC permissions for other types, such as Cluster and Machine. If you need read-only access, you can limit the permissions to get, list, and watch. You can use the following configuration for retrieving Cluster and Machine resources:

// +kubebuilder:rbac:groups=cluster.x-k8s.io,resources=clusters;clusters/status,verbs=get;list;watch
// +kubebuilder:rbac:groups=cluster.x-k8s.io,resources=machines;machines/status,verbs=get;list;watch

Cluster API controllers

The Cluster API controller for Machine resources is configured with full read/write RBAC permissions for all resources in the infrastructure.cluster.x-k8s.io API group. This group represents all machine infrastructure providers for SIG Cluster Lifecycle-sponsored provider subprojects. If you are writing a provider not sponsored by the SIG, you must grant full read/write RBAC permissions for the “infrastructure machine” resource in your API group to the Cluster API manager’s ServiceAccount. ClusterRoles can be granted using the aggregation label cluster.x-k8s.io/aggregate-to-manager: "true". The following is an example ClusterRole for a FooMachine resource:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: capi-foo-machines
  labels:
    cluster.x-k8s.io/aggregate-to-manager: "true"
rules:
- apiGroups:
  - infrastructure.foo.com
  resources:
  - foomachines
  verbs:
  - create
  - delete
  - get
  - list
  - patch
  - update
  - watch

Note, the write permissions allow the Machine controller to set owner references and labels on the “infrastructure machine” resources; they are not used for general mutations of these resources.

Bootstrap Provider Specification

Overview

A bootstrap provider generates bootstrap data that is used to bootstrap a Kubernetes node.

Data Types

Bootstrap API resource

A bootstrap provider must define an API type for bootstrap resources. The type:

1. Must belong to an API group served by the Kubernetes apiserver
2. May be implemented as a CustomResourceDefinition, or as part of an aggregated apiserver
3. Must be namespace-scoped
4. Must have the standard Kubernetes “type metadata” and “object metadata”
5. Should have a spec field containing fields relevant to the bootstrap provider
6. Must have a status field with the following:
   1. Required fields:
      1. ready (boolean): indicates the bootstrap data has been generated and is ready
      2. dataSecretName (string): the name of the secret that stores the generated bootstrap data
   2. Optional fields:
      1. failureReason (string): indicates there is a fatal problem reconciling the bootstrap data; meant to be suitable for programmatic interpretation
      2. failureMessage (string): indicates there is a fatal problem reconciling the bootstrap data; meant to be a more descriptive value than failureReason

Note: because the dataSecretName is part of status, this value must be deterministically recreatable from the data in the Cluster, Machine, and/or bootstrap resource. If the name is randomly generated, it is not always possible to move the resource and its associated secret from one management cluster to another.

Bootstrap Secret

The Secret containing bootstrap data must:

1. Use the API resource’s status.dataSecretName for its name
2. Have the label cluster.x-k8s.io/cluster-name set to the name of the cluster
3. Have a controller owner reference to the API resource
4. Have a single key, value, containing the bootstrap data

Behavior

A bootstrap provider must respond to changes to its bootstrap resources. This process is typically called reconciliation. The provider must watch for new, updated, and deleted resources and respond accordingly.

The following diagram shows the typical logic for a bootstrap provider:

1. If the resource does not have a Machine owner, exit the reconciliation
   1. The Cluster API Machine reconciler populates this based on the value in the Machine‘s spec.bootstrap.configRef field.
2. If the resource has status.failureReason or status.failureMessage set, exit the reconciliation
3. If the Cluster to which this resource belongs cannot be found, exit the reconciliation
4. Deterministically generate the name for the bootstrap data secret
5. Try to retrieve the Secret with the name from the previous step
   1. If it does not exist, generate bootstrap data and create the Secret
6. Set status.dataSecretName to the generated name
7. Set status.ready to true
8. Patch the resource to persist changes

RBAC

Provider controller

A bootstrap provider must have RBAC permissions for the types it defines, as well as the bootstrap data Secret resources it manages. If you are using kubebuilder to generate new API types, these permissions should be configured for you automatically. For example, the Kubeadm bootstrap provider the following configuration for its KubeadmConfig type:

// +kubebuilder:rbac:groups=bootstrap.cluster.x-k8s.io,resources=kubeadmconfigs;kubeadmconfigs/status,verbs=get;list;watch;create;update;patch;delete
// +kubebuilder:rbac:groups="",resources=secrets,verbs=get;list;watch;create;update;patch;delete

A bootstrap provider may also need RBAC permissions for other types, such as Cluster. If you need read-only access, you can limit the permissions to get, list, and watch. The following configuration can be used for retrieving Cluster resources:

// +kubebuilder:rbac:groups=cluster.x-k8s.io,resources=clusters;clusters/status,verbs=get;list;watch

Cluster API controllers

The Cluster API controller for Machine resources is configured with full read/write RBAC permissions for all resources in the bootstrap.cluster.x-k8s.io API group. This group represents all bootstrap providers for SIG Cluster Lifecycle-sponsored provider subprojects. If you are writing a provider not sponsored by the SIG, you must add new RBAC permissions for the Cluster API manager-role role, granting it full read/write access to the bootstrap resource in your API group.

Note, the write permissions allow the Machine controller to set owner references and labels on the bootstrap resources; they are not used for general mutations of these resources.

Overview

In order to demonstrate how to develop a new Cluster API provider we will use kubebuilder to create an example provider. For more information on kubebuilder and CRDs in general we highly recommend reading the Kubebuilder Book. Much of the information here was adapted directly from it.

This is an infrastructure provider - tasked with managing provider-specific resources for clusters and machines. There are also bootstrap providers, which turn machines into Kubernetes nodes.

Prerequisites

• Install kubectl
• Install kustomize
• Install kubebuilder

tl;dr

# Install kubectl
brew install kubernetes-cli

# Install kustomize
brew install kustomize

# Install kubectl
KUBECTL_VERSION=$(curl -sf https://storage.googleapis.com/kubernetes-release/release/stable.txt)
curl -fLO https://storage.googleapis.com/kubernetes-release/release/${KUBECTL_VERSION}/bin/linux/amd64/kubectl

# Install kustomize
OS_TYPE=linux
curl -sf https://api.github.com/repos/kubernetes-sigs/kustomize/releases/latest |\
  grep browser_download |\
  grep ${OS_TYPE} |\
  cut -d '"' -f 4 |\
  xargs curl -f -O -L
mv kustomize_*_${OS_TYPE}_amd64 /usr/local/bin/kustomize
chmod u+x /usr/local/bin/kustomize

# Install Kubebuilder
os=$(go env GOOS)
arch=$(go env GOARCH)

# download kubebuilder and extract it to tmp
curl -sL https://go.kubebuilder.io/dl/2.1.0/${os}/${arch} | tar -xz -C /tmp/

# move to a long-term location and put it on your path
# (you'll need to set the KUBEBUILDER_ASSETS env var if you put it somewhere else)
sudo mv /tmp/kubebuilder_2.1.0_${os}_${arch} /usr/local/kubebuilder
export PATH=$PATH:/usr/local/kubebuilder/bin

Repository Naming

The naming convention for new Cluster API provider repositories is generally of the form cluster-api-provider-${env}, where ${env} is a, possibly short, name for the environment in question. For example cluster-api-provider-gcp is an implementation for the Google Cloud Platform, and cluster-api-provider-aws is one for Amazon Web Services. Note that an environment may refer to a cloud, bare metal, virtual machines, or any other infrastructure hosting Kubernetes. Finally, a single environment may include more than one variant. So for example, cluster-api-provider-aws may include both an implementation based on EC2 as well as one based on their hosted EKS solution.

A note on Acronyms

Because these names end up being so long, developers of Cluster API frequently refer to providers by acronyms. Cluster API itself becomes CAPI, pronounced “Cappy.” cluster-api-provider-aws is CAPA, pronounced “KappA.” cluster-api-provider-gcp is CAPG, pronounced “Cap Gee,” and so on.

Resource Naming

For the purposes of this guide we will create a provider for a service named mailgun. Therefore the name of the repository will be cluster-api-provider-mailgun.

Every Kubernetes resource has a Group, Version and Kind that uniquely identifies it.

• The resource Group is similar to package in a language. It disambiguates different APIs that may happen to have identically named Kinds. Groups often contain a domain name, such as k8s.io. The domain for Cluster API resources is cluster.x-k8s.io, and infrastructure providers generally use infrastructure.cluster.x-k8s.io.
• The resource Version defines the stability of the API and its backward compatibility guarantees. Examples include v1alpha1, v1beta1, v1, etc. and are governed by the Kubernetes API Deprecation Policy ¹. Your provider should expect to abide by the same policies.
• The resource Kind is the name of the objects we’ll be creating and modifying. In this case it’s MailgunMachine and MailgunCluster.

For example, our cluster object will be:

apiVersion: infrastructure.cluster.x-k8s.io/v1alpha3
kind: MailgunCluster

Create a repository

mkdir cluster-api-provider-mailgun
cd src/sigs.k8s.io/cluster-api-provider-mailgun
git init

You’ll then need to set up go modules

$ go mod init github.com/liztio/cluster-api-provider-mailgun
go: creating new go.mod: module github.com/liztio/cluster-api-provider-mailgun

Generate scaffolding

kubebuilder init --domain cluster.x-k8s.io

kubebuilder init will create the basic repository layout, including a simple containerized manager. It will also initialize the external go libraries that will be required to build your project.

Commit your changes so far:

git commit -m "Generate scaffolding."

Generate provider resources for Clusters and Machines

Here you will be asked if you want to generate resources and controllers. You’ll want both of them:

kubebuilder create api --group infrastructure --version v1alpha3 --kind MailgunCluster
kubebuilder create api --group infrastructure --version v1alpha3 --kind MailgunMachine

Create Resource under pkg/apis [y/n]?
y
Create Controller under pkg/controller [y/n]?
y

Add Status subresource

The status subresource lets Spec and Status requests for custom resources be addressed separately so requests don’t conflict with each other. It also lets you split RBAC rules between Spec and Status. It’s stable in Kubernetes as of v1.16, but you will have to manually enable it in Kubebuilder.

Add the subresource:status annotation to your <provider>cluster_types.go <provider>machine_types.go

// +kubebuilder:subresource:status
// +kubebuilder:object:root=true

// MailgunCluster is the Schema for the mailgunclusters API
type MailgunCluster struct {

// +kubebuilder:subresource:status
// +kubebuilder:object:root=true

// MailgunMachine is the Schema for the mailgunmachines API
type MailgunMachine struct {

And regenerate the CRDs:

make manifests

Apply further customizations

The cluster API CRDs should be further customized:

• Apply the contract version label to support conversions
• Upgrade to CRD v1
• Set “matchPolicy=Equivalent” kubebuilder marker for webhooks
• Refactor the kustomize config folder to support multi-tenancy
• Ensure you are compliant with the clusterctl provider contract

Commit your changes

git add .
git commit -m "Generate Cluster and Machine resources."

Defining your API

The API generated by Kubebuilder is just a shell, your actual API will likely have more fields defined on it.

Kubernetes has a lot of conventions and requirements around API design. The Kubebuilder docs have some helpful hints on how to design your types.

Let’s take a look at what was generated for us:

// MailgunClusterSpec defines the desired state of MailgunCluster
type MailgunClusterSpec struct {
	// INSERT ADDITIONAL SPEC FIELDS - desired state of cluster
	// Important: Run "make" to regenerate code after modifying this file
}

// MailgunClusterStatus defines the observed state of MailgunCluster
type MailgunClusterStatus struct {
	// INSERT ADDITIONAL STATUS FIELD - define observed state of cluster
	// Important: Run "make" to regenerate code after modifying this file
}

Our API is based on Mailgun, so we’re going to have some email based fields:

type Priority string

const (
	// PriorityUrgent means do this right away
	PriorityUrgent = Priority("Urgent")

	// PriorityUrgent means do this immediately
	PriorityExtremelyUrgent = Priority("ExtremelyUrgent")

	// PriorityBusinessCritical means you absolutely need to do this now
	PriorityBusinessCritical = Priority("BusinessCritical")
)

// MailgunClusterSpec defines the desired state of MailgunCluster
type MailgunClusterSpec struct {
	// Priority is how quickly you need this cluster
	Priority Priority `json:"priority"`
	// Request is where you ask extra nicely
	Request string `json:"request"`
	// Requester is the email of the person sending the request
	Requester string `json:"requester"`
}

// MailgunClusterStatus defines the observed state of MailgunCluster
type MailgunClusterStatus struct {
	// MessageID is set to the message ID from Mailgun when our message has been sent
	MessageID *string `json:"response"`
}

As the deleted comments request, run make manager manifests to regenerate some of the generated data files afterwards.

git add .
git commit -m "Added cluster types"

Controllers and Reconciliation

From the kubebuilder book:

Controllers are the core of Kubernetes, and of any operator.

It’s a controller’s job to ensure that, for any given object, the actual state of the world (both the cluster state, and potentially external state like running containers for Kubelet or loadbalancers for a cloud provider) matches the desired state in the object. Each controller focuses on one root Kind, but may interact with other Kinds.

We call this process reconciling.

Right now, we can create objects in our API but we won’t do anything about it. Let’s fix that.

Let’s see the Code

Kubebuilder has created our first controller in controllers/mailguncluster_controller.go. Let’s take a look at what got generated:

// MailgunClusterReconciler reconciles a MailgunCluster object
type MailgunClusterReconciler struct {
	client.Client
	Log logr.Logger
}

// +kubebuilder:rbac:groups=infrastructure.cluster.x-k8s.io,resources=mailgunclusters,verbs=get;list;watch;create;update;patch;delete
// +kubebuilder:rbac:groups=infrastructure.cluster.x-k8s.io,resources=mailgunclusters/status,verbs=get;update;patch

func (r *MailgunClusterReconciler) Reconcile(req ctrl.Request) (ctrl.Result, error) {
	_ = context.Background()
	_ = r.Log.WithValues("mailguncluster", req.NamespacedName)

	// your logic here

	return ctrl.Result{}, nil
}

RBAC Roles

Those // +kubebuilder... lines tell kubebuilder to generate RBAC roles so the manager we’re writing can access its own managed resources. We also need to add roles that will let it retrieve (but not modify) Cluster API objects. So we’ll add another annotation for that:

// +kubebuilder:rbac:groups=infrastructure.cluster.x-k8s.io,resources=mailgunclusters,verbs=get;list;watch;create;update;patch;delete
// +kubebuilder:rbac:groups=infrastructure.cluster.x-k8s.io,resources=mailgunclusters/status,verbs=get;update;patch
// +kubebuilder:rbac:groups=cluster.x-k8s.io,resources=clusters;clusters/status,verbs=get;list;watch

Make sure to add the annotation to both MailgunClusterReconciler and MailgunMachineReconciler.

Regenerate the RBAC roles after you are done:

make manifests

State

Let’s focus on that struct first. First, a word of warning: no guarantees are made about parallel access, both on one machine or multiple machines. That means you should not store any important state in memory: if you need it, write it into a Kubernetes object and store it.

We’re going to be sending mail, so let’s add a few extra fields:

// MailgunClusterReconciler reconciles a MailgunCluster object
type MailgunClusterReconciler struct {
	client.Client
	Log       logr.Logger
	Mailgun   mailgun.Mailgun
	Recipient string
}

Reconciliation

Now it’s time for our Reconcile function. Reconcile is only passed a name, not an object, so let’s retrieve ours.

Here’s a naive example:

func (r *MailgunClusterReconciler) Reconcile(req ctrl.Request) (ctrl.Result, error) {
	ctx := context.Background()
	_ = r.Log.WithValues("mailguncluster", req.NamespacedName)

	var cluster infrastructurev1alpha3.MailgunCluster
	if err := r.Get(ctx, req.NamespacedName, &cluster); err != nil {
		return ctrl.Result{}, err
	}

	return ctrl.Result{}, nil
}

By returning an error, we request that our controller will get Reconcile() called again. That may not always be what we want - what if the object’s been deleted? So let’s check that:

var cluster infrastructurev1alpha3.MailgunCluster
if err := r.Get(ctx, req.NamespacedName, &cluster); err != nil {
    // 	import apierrors "k8s.io/apimachinery/pkg/api/errors"
    if apierrors.IsNotFound(err) {
        return ctrl.Result{}, nil
    }
    return ctrl.Result{}, err
}

Now, if this were any old kubebuilder project we’d be done, but in our case we have one more object to retrieve. Cluster API splits a cluster into two objects: the Cluster defined by Cluster API itself. We’ll want to retrieve that as well. Luckily, cluster API provides a helper for us.

cluster, err := util.GetOwnerCluster(ctx, r.Client, &mg)
if err != nil {
    return ctrl.Result{}, err

}

client-go versions

At the time this document was written, kubebuilder pulls client-go version 1.14.1 into go.mod (it looks like k8s.io/client-go v11.0.1-0.20190409021438-1a26190bd76a+incompatible).

If you encounter an error when compiling like:

../pkg/mod/k8s.io/client-go@v11.0.1-0.20190409021438-1a26190bd76a+incompatible/rest/request.go:598:31: not enough arguments in call to watch.NewStreamWatcher
    have (*versioned.Decoder)
    want (watch.Decoder, watch.Reporter)`

You may need to bump client-go. At time of writing, that means 1.15, which looks like: k8s.io/client-go v11.0.1-0.20190409021438-1a26190bd76a+incompatible.

The fun part

More Documentation: The Kubebuilder Book has some excellent documentation on many things, including how to write good controllers!

Now that we have our objects, it’s time to do something with them! This is where your provider really comes into it’s own. In our case, let’s try sending some mail:

subject := fmt.Sprintf("[%s] New Cluster %s requested", mgCluster.Spec.Priority, cluster.Name)
body := fmt.Sprint("Hello! One cluster please.\n\n%s\n", mgCluster.Spec.Request)

msg := mailgun.NewMessage(mgCluster.Spec.Requester, subject, body, r.Recipient)
_, _, err = r.Mailgun.Send(msg)
if err != nil {
    return ctrl.Result{}, err
}

Idempotency

But wait, this isn’t quite right. Reconcile() gets called periodically for updates, and any time any updates are made. That would mean we’re potentially sending an email every few minutes! This is an important thing about controllers: they need to be idempotent.

So in our case, we’ll store the result of sending a message, and then check to see if we’ve sent one before.

if mgCluster.Status.MessageID != nil {
    // We already sent a message, so skip reconciliation
    return ctrl.Result{}, nil
}

subject := fmt.Sprintf("[%s] New Cluster %s requested", mgCluster.Spec.Priority, cluster.Name)
body := fmt.Sprintf("Hello! One cluster please.\n\n%s\n", mgCluster.Spec.Request)

msg := mailgun.NewMessage(mgCluster.Spec.Requester, subject, body, r.Recipient)
_, msgID, err := r.Mailgun.Send(msg)
if err != nil {
    return ctrl.Result{}, err
}

// patch from sigs.k8s.io/cluster-api/util/patch
helper, err := patch.NewHelper(&mgCluster, r.Client)
if err != nil {
    return ctrl.Result{}, err
}
mgCluster.Status.MessageID = &msgID
if err := helper.Patch(ctx, &mgCluster); err != nil {
    return ctrl.Result{}, errors.Wrapf(err, "couldn't patch cluster %q", mgCluster.Name)
}

return ctrl.Result{}, nil

A note about the status

Usually, the Status field should only be fields that can be computed from existing state. Things like whether a machine is running can be retrieved from an API, and cluster status can be queried by a healthcheck. The message ID is ephemeral, so it should properly go in the Spec part of the object. Anything that can’t be recreated, either with some sort of deterministic generation method or by querying/observing actual state, needs to be in Spec. This is to support proper disaster recovery of resources. If you have a backup of your cluster and you want to restore it, Kubernetes doesn’t let you restore both spec & status together.

We use the MessageID as a Status here to illustrate how one might issue status updates in a real application.

Update main.go with your new fields

If you added fields to your reconciler, you’ll need to update main.go.

Right now, it probably looks like this:

if err = (&controllers.MailgunClusterReconciler{
    Client: mgr.GetClient(),
    Log:    ctrl.Log.WithName("controllers").WithName("MailgunCluster"),
}).SetupWithManager(mgr); err != nil {
    setupLog.Error(err, "unable to create controller", "controller", "MailgunCluster")
    os.Exit(1)
}

Let’s add our configuration. We’re going to use environment variables for this:

domain := os.Getenv("MAILGUN_DOMAIN")
if domain == "" {
    setupLog.Info("missing required env MAILGUN_DOMAIN")
    os.Exit(1)
}

apiKey := os.Getenv("MAILGUN_API_KEY")
if apiKey == "" {
    setupLog.Info("missing required env MAILGUN_API_KEY")
    os.Exit(1)
}

recipient := os.Getenv("MAIL_RECIPIENT")
if recipient == "" {
    setupLog.Info("missing required env MAIL_RECIPIENT")
    os.Exit(1)
}

mg := mailgun.NewMailgun(domain, apiKey)

if err = (&controllers.MailgunClusterReconciler{
    Client:    mgr.GetClient(),
    Log:       ctrl.Log.WithName("controllers").WithName("MailgunCluster"),
    Mailgun:   mg,
    Recipient: recipient,
}).SetupWithManager(mgr); err != nil {
    setupLog.Error(err, "unable to create controller", "controller", "MailgunCluster")
    os.Exit(1)
}

If you have some other state, you’ll want to initialize it here!

Building, Running, Testing

Docker Image Name

The patch in config/manager/manager_image_patch.yaml will be applied to the manager pod. Right now there is a placeholder IMAGE_URL, which you will need to change to your actual image.

Development Images

It’s likely that you will want one location and tag for release development, and another during development.

The approach most Cluster API projects is using a Makefile that uses sed to replace the image URL on demand during development.

Deployment

cert-manager

Cluster API uses cert-manager to manage the certificates it needs for its webhooks. Before you apply Cluster API’s yaml, you should install cert-manager

kubectl apply -f https://github.com/jetstack/cert-manager/releases/download/<version>/cert-manager.yaml

Cluster API

Before you can deploy the infrastructure controller, you’ll need to deploy Cluster API itself.

You can use a precompilaed manifest from the release page, or clone cluster-api and apply its manifests using kustomize.

cd cluster-api
kustomize build config/ | kubectl apply -f-

Check the status of the manager to make sure it’s running properly

$ kubectl describe -n capi-system pod | grep -A 5 Conditions
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True

Your provider

Now you can apply your provider as well:

$ cd cluster-api-provider-mailgun
$ kustomize build config/ | envsubst | kubectl apply -f-
$ kubectl describe -n cluster-api-provider-mailgun-system pod | grep -A 5 Conditions
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True

Tiltfile

Cluster API development requires a lot of iteration, and the “build, tag, push, update deployment” workflow can be very tedious. Tilt makes this process much simpler by watching for updates, then automatically building and deploying them.

You can visit some example repositories, but you can get started by writing out a yaml manifest and using the following Tiltfile kustomize build config/ | envsubst > capm.yaml

allow_k8s_contexts('kubernetes-admin@kind)

k8s_yaml('capm.yaml')

docker_build('<your docker username or repository url>/cluster-api-controller-mailgun-amd64', '.')

You can then use Tilt to watch the logs coming off your container

Your first Cluster

Let’s try our cluster out. We’ll make some simple YAML:

apiVersion: cluster.x-k8s.io/v1alpha2
kind: Cluster
metadata:
  name: hello-mailgun
spec:
  clusterNetwork:
    pods:
      cidrBlocks: ["192.168.0.0/16"]
  infrastructureRef:
    apiVersion: infrastructure.cluster.x-k8s.io/v1alpha3
    kind: MailgunCluster
    name: hello-mailgun
---
apiVersion: infrastructure.cluster.x-k8s.io/v1alpha3
kind: MailgunCluster
metadata:
  name: hello-mailgun
spec:
  priority: "ExtremelyUrgent"
  request: "Please make me a cluster, with sugar on top?"
  requester: "cluster-admin@example.com"

We apply it as normal with kubectl apply -f <filename>.yaml.

If all goes well, you should be getting an email to the address you configured when you set up your management cluster:

Conclusion

Obviously, this is only the first step. We need to implement our Machine object too, and log events, handle updates, and many more things.

Hopefully you feel empowered to go out and create your own provider now. The world is your Kubernetes-based oyster!

CustomResourceDefinitions relationships

There are many resources that appear in the Cluster API. In this section, we use diagrams to illustrate the most common relationships between Cluster API resources.

Control plane machines relationships

Worker machines relationships

Troubleshooting

Labeling nodes with reserved labels such as node-role.kubernetes.io fails with kubeadm error during bootstrap

Self-assigning Node labels such as node-role.kubernetes.io using the kubelet --node-labels flag (see kubeletExtraArgs in the CABPK examples) is not possible due to a security measure imposed by the NodeRestriction admission controller that kubeadm enables by default.

Assigning such labels to Nodes must be done after the bootstrap process has completed:

kubectl label nodes <name> node-role.kubernetes.io/worker=""

For convenience, here is an example one-liner to do this post installation

kubectl get nodes --no-headers -l '!node-role.kubernetes.io/master' -o jsonpath='{range .items[*]}{.metadata.name}{"\n"}' | xargs -I{} kubectl label node {} node-role.kubernetes.io/worker=''

Reference

This section contains various resources that define the Cluster API project.

Table of Contents

A | B | C | D | H | I | K | M | N | O | P | S | T | W

A

Add-ons

Services beyond the fundamental components of Kubernetes.

• Core Add-ons: Addons that are required to deploy a Kubernetes-conformant cluster: DNS, kube-proxy, CNI.
• Additional Add-ons: Addons that are not required for a Kubernetes-conformant cluster (e.g. metrics/Heapster, Dashboard).

B

Bootstrap

The process of turning a server into a Kubernetes node. This may involve assembling data to provide when creating the server that backs the Machine, as well as runtime configuration of the software running on that server.

Bootstrap cluster

A temporary cluster that is used to provision a Target Management cluster.

C

CAEP

Cluster API Enhancement Proposal - patterned after KEP. See template

CAPI

Core Cluster API

CAPA

Cluster API Provider AWS

CABPK

Cluster API Bootstrap Provider Kubeadm

CAPD

Cluster API Provider Docker

CAPG

Cluster API Google Cloud Provider

CAPIBM

Cluster API Provider IBM Cloud

CAPO

Cluster API Provider OpenStack

CAPV

Cluster API Provider vSphere

CAPZ

Cluster API Provider Azure

Cluster

A full Kubernetes deployment. See Management Cluster and Workload Cluster

Cluster API

Or Cluster API project

The Cluster API sub-project of the SIG-cluster-lifecycle. It is also used to refer to the software components, APIs, and community that produce them.

Control plane

The set of Kubernetes services that form the basis of a cluster. See also https://kubernetes.io/docs/concepts/#kubernetes-control-plane There are two variants:

• Self-provisioned: A Kubernetes control plane consisting of pods or machines wholly managed by a single Cluster API deployment.
• External: A control plane offered and controlled by some system other than Cluster API (e.g., GKE, AKS, EKS, IKS).

D

Default implementation

A feature implementation offered as part of the Cluster API project, infrastructure providers can swap it out for a different one.

H

Horizontal Scaling

The ability to add more machines based on policy and well defined metrics. For example, add a machine to a cluster when CPU load average > (X) for a period of time (Y).

Host

see Server

I

Infrastructure provider

A source of computational resources (e.g. machines, networking, etc.). Examples for cloud include AWS, Azure, Google, etc.; for bare metal include VMware, MAAS, metal3.io, etc. When there is more than one way to obtain resources from the same infrastructure provider (e.g. EC2 vs. EKS) each way is referred to as a variant.

Instance

see Server

Immutability

A resource that does not mutate. In kubernetes we often state the instance of a running pod is immutable or does not change once it is run. In order to make a change, a new pod is run. In the context of Cluster API we often refer to a running instance of a Machine as being immutable, from a Cluster API perspective.

K

Kubernetes-conformant

Or Kubernetes-compliant

A cluster that passes the Kubernetes conformance tests.

k/k

Refers to the main Kubernetes git repository or the main Kubernetes project.

M

Machine

Or Machine Resource

The Custom Resource for Kubernetes that represents a request to have a place to run kubelet.

See also: Server

Manage a cluster

Perform create, scale, upgrade, or destroy operations on the cluster.

Management cluster

The cluster where one or more Infrastructure Providers run, and where resources (e.g. Machines) are stored. Typically referred to when you are provisioning multiple workload clusters.

Management group

A management group is a group of providers composed by a CoreProvider and a set of Bootstrap/ControlPlane/Infrastructure providers watching objects in the same namespace. For example, a management group can be used for upgrades, in order to ensure all the providers in a management group support the same Cluster API version.

N

Node pools

A node pool is a group of nodes within a cluster that all have the same configuration.

O

Operating system

Or OS

A generically understood combination of a kernel and system-level userspace interface, such as Linux or Windows, as opposed to a particular distribution.

P

Pivot

Pivot is a process for moving the provider components and declared cluster-api resources from a Source Management cluster to a Target Management cluster.

The pivot process is also used for deleting a management cluster and could also be used during an upgrade of the management cluster.

Provider

See Infrastructure Provider

Provider components

Refers to the YAML artifact a provider publishes as part of their releases which is required to use the provider components, it usually contains Custom Resource Definitions (CRDs), Deployments (to run the controller manager), RBAC, etc.

Provider implementation

Existing Cluster API implementations consist of generic and infrastructure provider-specific logic. The infrastructure provider-specific logic is currently maintained in infrastructure provider repositories.

S

Scaling

Unless otherwise specified, this refers to horizontal scaling.

Stacked control plane

A control plane node where etcd is colocated with the Kubernetes API server, and is running as a static pod.

Server

The infrastructure that backs a Machine Resource, typically either a cloud instance, virtual machine, or physical host.

W

Workload Cluster

A cluster created by a ClusterAPI controller, which is not a bootstrap cluster, and is meant to be used by end-users, as opposed to by CAPI tooling.

Provider Implementations

The code in this repository is independent of any specific deployment environment. Provider specific code is being developed in separate repositories, some of which are also sponsored by SIG Cluster Lifecycle. Check provider’s documentation for updated info about which API version they are supporting.

Bootstrap

• Kubeadm
• Talos
• EKS

Infrastructure

• Alibaba Cloud
• AWS
• Azure
• Azure Stack HCI
• Baidu Cloud
• Metal3
• DigitalOcean
• Exoscale
• GCP
• IBM Cloud
• OpenStack
• Packet
• Sidero
• Tencent Cloud
• vSphere

API Adopters

Following are the implementations managed by third-parties adopting the standard cluster-api and/or machine-api being developed here.

• Kubermatic machine controller
• Machine API Operator
• Machine controller manager

Ports used by Cluster API

Note: external providers (e.g. infrastructure, bootstrap, or control-plane) might allocate ports differently, please refer to the respective documentation.

Kubernetes Community Code of Conduct

Please refer to our Kubernetes Community Code of Conduct

Contributing Guidelines

• Contributing Guidelines
  • Contributor License Agreements
  • Finding Things That Need Help
  • Contributing a Patch
  • Reviewing a Patch
    • Approvals
  • Reviews
  • Backporting a Patch
  • Features and bugs
  • Proposal process (CAEP)
  • Experiments
  • Breaking Changes
  • Google Doc Viewing Permissions
  • Issue and Pull Request Management

Read the following guide if you’re interested in contributing to cluster-api.

Contributor License Agreements

We’d love to accept your patches! Before we can take them, we have to jump a couple of legal hurdles.

Please fill out either the individual or corporate Contributor License Agreement (CLA). More information about the CLA and instructions for signing it can be found here.

NOTE: Only original source code from you and other people that have signed the CLA can be accepted into the *repository.

Finding Things That Need Help

If you’re new to the project and want to help, but don’t know where to start, we have a semi-curated list of issues that should not need deep knowledge of the system. Have a look and see if anything sounds interesting. Before starting to work on the issue, make sure that it doesn’t have a lifecycle/active label. If the issue has been assigned, reach out to the assignee. Alternatively, read some of the docs on other controllers and try to write your own, file and fix any/all issues that come up, including gaps in documentation!

Contributing a Patch

1. If you haven’t already done so, sign a Contributor License Agreement (see details above).
2. If working on an issue, signal other contributors that you are actively working on it using /lifecycle active.
3. Fork the desired repo, develop and test your code changes.
4. Submit a pull request.
   1. All code PR must be labeled with one of
      • ⚠️ (:warning:, major or breaking changes)
      • ✨ (:sparkles:, feature additions)
      • 🐛 (:bug:, patch and bugfixes)
      • 📖 (:book:, documentation or proposals)
      • 🌱 (:seedling:, minor or other)

All changes must be code reviewed. Coding conventions and standards are explained in the official developer docs. Expect reviewers to request that you avoid common go style mistakes in your PRs.

Triaging E2E test failures

When you submit a change to the Cluster API repository as set of validation jobs is automatically executed by prow and the results report is added to a comment at the end of your PR.

Some jobs run linters or unit test, and in case of failures, you can repeat the same operation locally using make test lint-full [etc..] in order to investigate and potential issues. Prow logs usually provide hints about the make target you should use
(there might be more than one command that needs to be run).

End-to-end (E2E) jobs create real Kubernetes clusters by building Cluster API artifacts with the latest changes. In case of E2E test failures, usually it’s required to access the “Artifacts” link on the top of the prow logs page to triage the problem.

The artifact folder contains:

• A folder with the clusterctl local repository used for the test, where you can find components yaml and cluster templates.
• A folder with logs for all the clusters created during the test. Following logs/info are available:
  • Controller logs (only if the cluster is a management cluster).
  • Dump of the Cluster API resources (only if the cluster is a management cluster).
  • Machine logs (only if the cluster is a workload cluster)

In case you want to run E2E test locally, please refer to the Testing guide.

Reviewing a Patch

Reviews

Parts of the following content have been adapted from https://google.github.io/eng-practices/review.

Any Kubernetes organization member can leave reviews and /lgtm a pull request.

Code reviews should generally look at:

• Design: Is the code well-designed and consistent with the rest of the system?
• Functionality: Does the code behave as the author (or linked issue) intended? Is the way the code behaves good for its users?
• Complexity: Could the code be made simpler? Would another developer be able to easily understand and use this code when they come across it in the future?
• Tests: Does the code have correct and well-designed tests?
• Naming: Did the developer choose clear names for variable, types, methods, functions, etc.?
• Comments: Are the comments clear and useful? Do they explain the why rather than what?
• Documentation: Did the developer also update relevant documentation?

See Code Review in Cluster API for a more focused list of review items.

Approvals

Please see the Kubernetes community document on pull requests for more information about the merge process.

• A PR is approved by one of the project maintainers and owners after reviews.
• Approvals should be the very last action a maintainer takes on a pull request.

Backporting a Patch

Cluster API maintains older versions through release-X.Y branches. We accept backports of bug fixes to the most recent release branch. For example, if the most recent branch is release-0.2, and the master branch is under active development for v0.3.0, a bug fix that merged to master that also affects v0.2.x may be considered for backporting to release-0.2. We generally do not accept PRs against older release branches.

Features and bugs

Open issues to report bugs, or minor features.

For big feature, API and contract amendments, we follow the CAEP process as outlined below.

Proposal process (CAEP)

The Cluster API Enhacement Proposal is the process this project uses to adopt new features, or changes to the APIs.

• The template, and accepted proposals live under docs/proposals.
• A proposal SHOULD be introduced and discussed during the weekly community meetings, Kubernetes SIG Cluster Lifecycle mailing list, or discuss forum.
• A proposal SHOULD be submitted first to the community using a collaborative writing platform, preferably Google Docs.
  • When using Google Docs, share the document with edit permissions for the Kubernetes SIG Cluster Lifecycle mailing list.

Experiments

Proof of concepts, code experiments, or other initiatives can live under the exp folder and behind a feature gate.

• Experiments SHOULD not modify any of the publicly exposed APIs (e.g. CRDs).
• Experiments SHOULD not modify any existing CRD types outside of the experimental API group(s).
• Experiments SHOULD not modify any existing command line contracts.
• Experiments MUST not cause any breaking changes to existing (non-experimental) Go APIs.
• Experiments SHOULD introduce utility helpers in the go APIs for experiments that cross multiple components and require support from bootstrap, control plane, or infrastructure providers.
• Experiments follow a strict lifecycle: Alpha -> Beta prior to Graduation.
  • Alpha-stage experiments:
    • SHOULD not be enabled by default and any feature gates MUST be marked as ‘Alpha’
    • MUST be associated with a CAEP that is merged and in at least a provisional state
    • MAY be considered inactive and marked as deprecated if the following does not happen within the course of 1 minor release cycle:
      • Transition to Beta-stage
      • Active development towards progressing to Beta-stage
      • Either direct or downstream user evaluation
    • Any deprecated Alpha-stage experiment MAY be removed in the next minor release.
  • Beta-stage experiments:
    • SHOULD be enabled by default, and any feature gates MUST be marked as ‘Beta’
    • MUST be associated with a CAEP that is at least in the experimental state
    • MUST support conversions for any type changes
    • MUST remain backwards compatible unless updates are coinciding with a breaking Cluster API release
    • MAY be considered inactive and marked as deprecated if the following does not happen within the course of 1 minor release cycle:
      • Graduate
      • Active development towards Graduation
      • Either direct or downstream user consumption
    • Any deprecated Beta-stage experiment MAY be removed after being deprecated for an entire minor release.
• Experiment Graduation MUST coincide with a breaking Cluster API release
• Experiment Graduation checklist:
  • MAY provide a way to be disabled, any feature gates MUST be marked as ‘GA’
  • MUST undergo a full Kubernetes-style API review and update the CAEP with the plan to address any issues raised
  • CAEP MUST be in an implementable state and is fully up to date with the current implementation
  • CAEP MUST define transition plan for moving out of the experimental api group and code directories
  • CAEP MUST define any upgrade steps required for Existing Management and Workload Clusters
  • CAEP MUST define any upgrade steps required to be implemented by out-of-tree bootstrap, control plane, and infrastructure providers.

Breaking Changes

Breaking changes are generally allowed in the master branch, as this is the branch used to develop the next minor release of Cluster API.

There may be times, however, when master is closed for breaking changes. This is likely to happen as we near the release of a new minor version.

Breaking changes are not allowed in release branches, as these represent minor versions that have already been released. These versions have consumers who expect the APIs, behaviors, etc. to remain stable during the life time of the patch stream for the minor release.

Examples of breaking changes include:

• Removing or renaming a field in a CRD
• Removing or renaming a CRD
• Removing or renaming an exported constant, variable, type, or function
• Updating the version of critical libraries such as controller-runtime, client-go, apimachinery, etc.
  • Some version updates may be acceptable, for picking up bug fixes, but maintainers must exercise caution when reviewing.

There may, at times, need to be exceptions where breaking changes are allowed in release branches. These are at the discretion of the project’s maintainers, and must be carefully considered before merging. An example of an allowed breaking change might be a fix for a behavioral bug that was released in an initial minor version (such as v0.3.0).

Google Doc Viewing Permissions

To gain viewing permissions to google docs in this project, please join either the kubernetes-dev or kubernetes-sig-cluster-lifecycle google group.

Issue and Pull Request Management

Anyone may comment on issues and submit reviews for pull requests. However, in order to be assigned an issue or pull request, you must be a member of the Kubernetes SIGs GitHub organization.

If you are a Kubernetes GitHub organization member, you are eligible for membership in the Kubernetes SIGs GitHub organization and can request membership by opening an issue against the kubernetes/org repo.

However, if you are a member of any of the related Kubernetes GitHub organizations but not of the Kubernetes org, you will need explicit sponsorship for your membership request. You can read more about Kubernetes membership and sponsorship here.

Cluster API maintainers can assign you an issue or pull request by leaving a /assign <your Github ID> comment on the issue or pull request.

Code Review in Cluster API

Goal of this document

• To help newcomers to the project in implementing better PRs given the knowledge of what will be evaluated during the review.
• To help contributors in stepping up as a reviewer given a common understanding of what are the most relevant things to be evaluated during the review.

IMPORTANT: improving and maintaining this document is a collaborative effort, so we are encouraging constructive feedback and suggestions.

• Code Review in Cluster API
  • Goal of this document
  • Resources
  • Definition
    • Controller reentrancy
    • API design
      • Serialization
      • Owner References
    • The Cluster API contract
    • Logging

Resources

• Writing inclusive documentation
• Contributor Summit NA 2019: Keeping the Bar High - How to be a bad ass Code Reviewer
• Code Review Developer Guide - Google
• The Gentle Art Of Patch Review

Definition

(from Code Review Developer Guide - Google)

“A code review is a process where someone other than the author(s) of a piece of code examines that code”

Within the context of cluster API the following design items should be carefully evaluated when reviewing a PR:

Controller reentrancy

In CAPI most of the coding activities happen in controllers, and in order to make robust controllers, we should strive for implementing reentrant code.

A reentrant code can be interrupted in the middle of its execution and then safely be called again (”re-entered”); this concept, applied to Kubernetes controllers, means that a controller should be capable of recovering from interruptions, observe the current state of things, and act accordingly. e.g.

• We should not rely on flags/conditions from previous reconciliations since we are the controller setting the conditions. Instead, we should detect the status of things through introspection at every reconciliation and act accordingly.
• It is acceptable to rely on status flags/conditions that we’ve previously set as part of the current reconciliation.
• It is acceptable to rely on status flags/conditions set by other controllers.

NOTE: An important use case for reentrancy is the move operation, where Cluster API objects gets moved to a different management cluster and the controller running on the target cluster has to rebuild the object status from scratch by observing the current state of the underlying infrastructure.

API design

The API defines the main contract with the Cluster API users. As most of the APIs in Kubernetes, each API version encompasses a set of guarantees to the user in terms of support window, stability, and upgradability.

This makes API design a critical part of Cluster API development and usually:

• Breaking/major API changes should go through the CAEP process and be strictly synchronized with the major release cadence.
• Non-breaking/minor API changes can go in minor releases; non-breaking changes are generally:
  • additive in nature
  • default to pre-existing behavior
  • optional as part of the API contract

On top of that, following API design considerations apply.

Serialization

The Kubernetes API-machinery that is used for API serialization is build on top of three technologies, most specifically:

• JSON serialization
• Open-API (for CRDs)
• the go type system

One of the areas where the interaction between those technologies is critical in the handling of optional values in the API; also the usage of nested slices might lead to problems in case of concurrent edits of the object.

Owner References

Cluster API leverages the owner ref chain of objects for several tasks, so it is crucial to evaluate the impacts of any change that can impact this area. Above all:

• The delete operation leverages on the owner ref chain for ensuring the cleanup of all the resources when a cluster is deleted;
• clusterctl move uses the owner ref chain for determining which object to move and the create/delete order.

The Cluster API contract

The Cluster API rules define a set of rules/conventions the different provider authors should follow in order to implement providers that can interact with the core Cluster API controllers, as documented here and here.

By extension, the Cluster API contract includes all the util methods that Cluster API exposes for making the development of providers simpler and consistent (e.g. everything under /util or in /test/framework); documentation of the utility is available here.

The Cluster API contract is linked to the version of the API (e.g. v1alpha3 Contract), and it is expected to provide the same set of guarantees in terms of support window, stability, and upgradability.

This makes any change that can impact the Cluster API contract critical and usually:

• Breaking/major contract changes should go through the CAEP process and be strictly synchronized with the major release cadence.
• Non-breaking/minor changes can go in minor releases; non-breaking changes are generally:
  • Additive in nature
  • Default to pre-existing behavior
  • Optional as part of the API contract

Logging

• For CAPI controllers see Kubernetes logging conventions.
• For clusterctl see clusterctl logging conventions.

Testing

Testing plays an crucial role in ensuring the long term maintainability of the project.

In Cluster API we are committed to have a good test coverage and also to have a nice and consistent style in implementing tests. For more information see testing Cluster API.

Cluster API Version Support and Kubernetes Version Skew Policy

Supported Versions

The Cluster API team maintains release branches for (v1alpha3) v0.3 and (v1alpha2) v0.2, the two most recent releases.

Releases include these components:

• Core Provider
• Kubeadm Bootstrap Provider
• Kubeadm Control Plane Provider
• clusterctl client

All Infrastructure Providers are maintained by independent teams. Other Bootstrap and Control Plane Providers are also maintained by independent teams. For more information about their version support, see below.

Supported Kubernetes Versions

The project aims to keep the current minor release compatible with the actively supported Kubernetes minor releases, i.e., the current release (N), N-1, and N-2. To find out the exact range of Kubernetes versions supported by each component, please see the tables below.

See the following section to understand how cluster topology affects version support.

Kubernetes Version Support As A Function Of Cluster Topology

The Core Provider, Kubeadm Bootstrap Provider, and Kubeadm Control Plane Provider run on the Management Cluster, and clusterctl talks to that cluster’s API server.

In some cases, the Management Cluster is separate from the Workload Clusters. The Kubernetes version of the Management and Workload Clusters are allowed to be different. For example, the current Cluster API release is compatible with Kubernetes versions 1.16 through 1.18. For example, the Management Cluster can run v1.18.2, and two Workload Clusters can run v1.16.9 and v1.17.5.

Management Clusters and Workload Clusters can be upgraded independently and in any order, however, if you are additionally moving from v1alpha2 (v0.2.x) to v1alpha3 (v0.3.x) as part of the upgrade roll out, the management cluster will need to be upgraded to at least v1.16.x, prior to upgrading any workload cluster using Cluster API v1alpha3 (v0.3.x)

These diagrams show the relationships between components in a Cluster API release (yellow), and other components (white).

Management And Workload Cluster Are the Same (Self-hosted)

Management And Workload Clusters Are Separate

Release Components

Core Provider (cluster-api-controller)

The Core Provider also talks to API server of every Workload Cluster. Therefore, the Workload Cluster’s Kubernetes version must also be compatible.

Kubeadm Bootstrap Provider (kubeadm-bootstrap-controller)

The Kubeadm Bootstrap Provider generates configuration using the v1beta1 or v1beta2 kubeadm API according to the target Kubernetes version.

Kubeadm Control Plane Provider (kubeadm-control-plane-controller)

The Kubeadm Control Plane Provider talks to the API server and etcd members of every Workload Cluster whose control plane it owns. It uses the etcd v3 API.

The Kubeadm Control Plane requires the Kubeadm Bootstrap Provider.

clusterctl

It is strongly recommended to always use the latest version of clusterctl, in order to get all the fixes/latest changes.

In case of upgrades, clusterctl should be upgraded first and then used to upgrade all the other components.

Providers Maintained By Independent Teams

In general, if a Provider version M says it is compatible with Cluster API version N, then version M must be compatible with a subset of the Kubernetes versions supported by Cluster API version N.

To understand the version compatibility of a specific provider, please see its documentation. This book includes a list of independent providers

Cluster API Roadmap

This roadmap is a constant work in progress, subject to frequent revision. Dates are approximations.

v0.3.7 (v1alpha3+) ~ June/July 2020

v0.4 (v1alpha4) ~ Q4 2020

v1beta1/v1 ~ TBA

Backlog

Items within this category have been identified as potential candidates for the project and can be moved up into a milestone if there is enough interest.