Audit code for Kubernetes-version specific handling

[sbueringer]

Goal of this issue is to audit all code in core Cluster API for Kubernetes version-specific handling and come up with an overview with which Kubernetes (and estimated Cluster API) version we can drop which code.

Tasks:

• Audit code and write overview
  • Overview should be structured by provider and Kubernetes (and estimated Cluster API) version
• This should include:
  • the remaining tasks of Rename references to "node-role.kubernetes.io/master" #3279 (kubeadm label & annotation migration)
    • Remove handling for nodeRoleOldControlPlane in test/framework
  • CRS controller should wait for the 'kubernetes' service ready before reconciling CRS objects #7804 (comment)
  • CRS: drop ensureKubernetesServiceCreated
  • KCP
    • Can we drop the cgroup driver override? 🌱 KCP: remove code handling Kubernetes <= v1.21 #11146 (comment)
    • Webhook validation code for 1.19:

      cluster-api/controlplane/kubeadm/internal/webhooks/kubeadm_control_plane.go

      Lines 708 to 719 in 42e26cb

      	// Check if we're trying to upgrade to Kubernetes v1.19.0, which is not supported.
      	//
      	// See https://github.com/kubernetes-sigs/cluster-api/issues/3564
      	if fromVersion.NE(toVersion) && toVersion.Equals(semver.MustParse("1.19.0")) {
      	allErrs = append(allErrs,
      	field.Forbidden(
      	field.NewPath("spec", "version"),
      	"cannot update Kubernetes version to v1.19.0, for more information see https://github.com/kubernetes-sigs/cluster-api/issues/3564",
      	),
      	)
      	return allErrs
      	}

    • Webhook validation code for v1.22-v1.24:

      cluster-api/controlplane/kubeadm/internal/webhooks/kubeadm_control_plane.go

      Lines 747 to 762 in 42e26cb

      	if (newK.Spec.KubeadmConfigSpec.ClusterConfiguration == nil ||
      	newK.Spec.KubeadmConfigSpec.ClusterConfiguration.ImageRepository == "") &&
      	// the version changed (i.e. we have an upgrade),
      	toVersion.NE(fromVersion) &&
      	// the version is >= v1.22.0 and < v1.26.0
      	toVersion.GTE(kubeadm.MinKubernetesVersionImageRegistryMigration) &&
      	toVersion.LT(kubeadm.NextKubernetesVersionImageRegistryMigration) &&
      	// and the default registry of the new Kubernetes/kubeadm version is the old default registry.
      	kubeadm.GetDefaultRegistry(toVersion) == kubeadm.OldDefaultImageRepository {
      	allErrs = append(allErrs,
      	field.Forbidden(
      	field.NewPath("spec", "version"),
      	"cannot upgrade to a Kubernetes/kubeadm version which is using the old default registry. Please use a newer Kubernetes patch release which is using the new default registry (>= v1.22.17, >= v1.23.15, >= v1.24.9)",
      	),
      	)
      	}

• Check test extension for Kubernetes version handling
• [opt] consider if/how we can add this activity to the release cycle tasks
• [opt] create separate tasks to drop code
• Add TODO markers for versions we can drop at a certain point
• When v1.33 or v1.34 is our min supported mgmt cluster version we should replace some of our Pattern validation with CEL (e.g. RFC 1123 label/subdomain): ⚠️ Restructure classRef field in Cluster.spec.topology #12235 (comment) (helps to avoid mistakes in the regexp patterns)

/kind cleanup

[sbueringer]

I intentionally added this to the v1.5 milestone as we won't start this activity before then and it would be good to have for v1.5

[fabriziopandini]

/triage accepted
/help

[sbueringer]

/remove-help

I'll be working on this one

[fabriziopandini]

/priority important-longterm