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 status object must have several fields defined:

  • ready - a boolean field that is true when the infrastructure is ready to be used.
  • apiEndpoints - a slice of strings that identifies each control plane node’s apiserver endpoint or a slice with only one endpoint that is a load balancer for all control plane nodes.

Optional status fields

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

  • errorReason - is a string that explains why an error has occurred, if possible.
  • errorMessage - is a string that holds the message contained by the error.

Example:

kind: MyProviderCluster
apiVersion: infrastructure.cluster.x-k8s.io/v1alpha2
status:
    ready: true
    apiEndpoints:
    - host: example.com
      port: 3333
    - host: example.com
      port: 3334

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.

Secret nameField nameContent
<cluster-name>-catls.crtbase64 encoded TLS certificate in PEM format
<cluster-name>-catls.keybase64 encoded TLS private key in PEM format

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

Secret nameField nameContent
<cluster-name>-kubeconfigvaluebase64 encoded kubeconfig