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Migration to ClusterClass

From #600, this repository uses CAPI ClusterClass feature for the creation of new clusters, additionally see k8s blog. This feature is also used e.g. in the SCS cluster-stacks repository.

Note: For now, ClusterClass is created per Cluster, which is not optimal and most likely it can be improved.

Therefore, existing clusters must be migrated from 'old' cluster templates to 'new' cluster class based templates. Based on ClusterClass proposal of update strategy, we shouldn't be able to migrate, but in CAPI PR #6292 the validation webhook was relaxed (via special Cluster annotation unsafe.topology.cluster.x-k8s.io/disable-update-class-name-check) and manual migration is now possible.

The script migrate-to-cluster-class.sh uses that special annotation for migration. In the beginning, it patches CAPI and KCP deployments with the ClusterTopology=true container argument. Then creates new resources (KubeadmControlPlaneTemplate, OpenStackClusterTemplate, ClusterClass). After that, annotates, labels and patches existing cluster resources. In the end, it patches the Cluster object with .spec.topology and it's done.

Migration​

Prerequisites​

  • CAPI >= v1.5.2 due to NamingStrategy feature
    • upgrade can be performed as stated in upgrade guide

Steps​

  1. Git pull/checkout new changes into the ~/k8s-cluster-api-provider directory
  2. Run migrate-to-cluster-class.sh <CLUSTER_NAME> (verify machines were not recreated)
  3. Copy new templates for existing and new clusters (consider backup) 
    cp ~/k8s-cluster-api-provider/terraform/files/template/cluster-template.yaml ~/<CLUSTER_NAME>/cluster-template.yaml
    cp ~/k8s-cluster-api-provider/terraform/files/template/cluster-template.yaml ~/cluster-defaults/cluster-template.yaml
  4. Add the newly introduced generation counter for the OpenStackClusterTemplate to the settings in clusterctl.yaml 
    echo "OPENSTACK_CLUSTER_GEN: geno01" >> ~/<CLUSTER_NAME>/clusterctl.yaml
    echo "OPENSTACK_CLUSTER_GEN: geno01" >> ~/cluster-defaults/clusterctl.yaml
  5. Next run of create_cluster.sh <CLUSTER_NAME> should be idempotent