awsmanagedcontrolplane: add status.version, implement version population for CAPI's MachineSetPreflightCheck

In the latest version, CAPI has turned on by default the MachineSetPreflightCheck feature,
which now enforces the managed ControPlane object spec and status to have a new Version field (more details on the API change https://cluster-api.sigs.k8s.io/developer/providers/contracts/control-plane#controlplane-version).

See: #5225

Also more conversation details with the core CAPI maintainers: https://kubernetes.slack.com/archives/CD6U2V71N/p1739783013734149

Author: damdo

config/crd/bases/controlplane.cluster.x-k8s.io_awsmanagedcontrolplanes.yaml

@@ -4115,6 +4115,11 @@ spec:
                   Ready denotes that the AWSManagedControlPlane API Server is ready to
                   receive requests and that the VPC infra is ready.
                 type: boolean
+              version:
+                description: |-
+                  Version represents the minimum Kubernetes version for the control plane machines
+                  in the cluster.
+                type: string
             required:
             - ready
             type: object

controlplane/eks/api/v1beta1/conversion.go

@@ -21,6 +21,7 @@ import (
 	infrav1beta1 "sigs.k8s.io/cluster-api-provider-aws/v2/api/v1beta1"
 	infrav1beta2 "sigs.k8s.io/cluster-api-provider-aws/v2/api/v1beta2"
 	ekscontrolplanev1 "sigs.k8s.io/cluster-api-provider-aws/v2/controlplane/eks/api/v1beta2"
+	v1beta2 "sigs.k8s.io/cluster-api-provider-aws/v2/controlplane/eks/api/v1beta2"
 	utilconversion "sigs.k8s.io/cluster-api/util/conversion"
 	"sigs.k8s.io/controller-runtime/pkg/conversion"
 )
@@ -41,6 +42,7 @@ func (r *AWSManagedControlPlane) ConvertTo(dstRaw conversion.Hub) error {
 	dst.Spec.VpcCni.Disable = r.Spec.DisableVPCCNI
 	dst.Spec.Partition = restored.Spec.Partition
 	dst.Spec.RestrictPrivateSubnets = restored.Spec.RestrictPrivateSubnets
+	dst.Status.Version = restored.Status.Version
 
 	return nil
 }
@@ -117,3 +119,8 @@ func Convert_v1beta2_VpcCni_To_v1beta1_VpcCni(in *ekscontrolplanev1.VpcCni, out
 func Convert_v1beta2_AWSManagedControlPlaneSpec_To_v1beta1_AWSManagedControlPlaneSpec(in *ekscontrolplanev1.AWSManagedControlPlaneSpec, out *AWSManagedControlPlaneSpec, scope apiconversion.Scope) error {
 	return autoConvert_v1beta2_AWSManagedControlPlaneSpec_To_v1beta1_AWSManagedControlPlaneSpec(in, out, scope)
 }
+
+// Convert_v1beta2_AWSManagedControlPlaneStatus_To_v1beta1_AWSManagedControlPlaneStatus is an autogenerated conversion function.
+func Convert_v1beta2_AWSManagedControlPlaneStatus_To_v1beta1_AWSManagedControlPlaneStatus(in *v1beta2.AWSManagedControlPlaneStatus, out *AWSManagedControlPlaneStatus, s apiconversion.Scope) error {
+	return autoConvert_v1beta2_AWSManagedControlPlaneStatus_To_v1beta1_AWSManagedControlPlaneStatus(in, out, s)
+}

controlplane/eks/api/v1beta1/zz_generated.conversion.go

@@ -283,6 +283,10 @@ type AWSManagedControlPlaneStatus struct {
 	// associated identity provider
 	// +optional
 	IdentityProviderStatus IdentityProviderStatus `json:"identityProviderStatus,omitempty"`
+	// Version represents the minimum Kubernetes version for the control plane machines
+	// in the cluster.
+	// +optional
+	Version *string `json:"version,omitempty"`
 }
 
 // +kubebuilder:object:root=true

controlplane/eks/api/v1beta2/awsmanagedcontrolplane_types.go

@@ -26,11 +26,13 @@ import (
 	"github.com/aws/aws-sdk-go/aws/awserr"
 	"github.com/aws/aws-sdk-go/aws/request"
 	"github.com/aws/aws-sdk-go/service/eks"
+	"github.com/blang/semver"
 	"github.com/go-logr/logr"
 	"github.com/pkg/errors"
 	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/apimachinery/pkg/util/version"
 	"k8s.io/klog/v2"
+	"k8s.io/utils/ptr"
 
 	infrav1 "sigs.k8s.io/cluster-api-provider-aws/v2/api/v1beta2"
 	ekscontrolplanev1 "sigs.k8s.io/cluster-api-provider-aws/v2/controlplane/eks/api/v1beta2"
@@ -140,7 +142,54 @@ func (s *Service) reconcileCluster(ctx context.Context) error {
 	return nil
 }
 
+// computeCurrentStatusVersion returns the computed current EKS cluster kubernetes version.
+// The computation has awareness of the fact that EKS clusters only return a major.minor kubernetes version,
+// and returns a compatible version for te status according to the one the user specified in the spec.
+func computeCurrentStatusVersion(specV *string, clusterV *string) *string {
+	specVersion := ""
+	if specV != nil {
+		specVersion = *specV
+	}
+
+	clusterVersion := ""
+	if clusterV != nil {
+		clusterVersion = *clusterV
+	}
+
+	// Ignore parsing errors as these are already validated by the kubebuilder validation and the AWS API.
+	// Also specVersion might not be specified in the spec.Version for AWSManagedControlPlane, this results in a "0.0.0" version.
+	// Also clusterVersion might not yet be returned by the AWS EKS API, as the cluster might still be initializing, this results in a "0.0.0" version.
+	specSemverVersion, _ := semver.ParseTolerant(specVersion)
+	currentSemverVersion, _ := semver.ParseTolerant(clusterVersion)
+
+	// If AWS EKS API is not returning a version, set the status.Version to empty string.
+	if currentSemverVersion.String() == "0.0.0" {
+		return ptr.To("")
+	}
+
+	if currentSemverVersion.Major == specSemverVersion.Major &&
+		currentSemverVersion.Minor == specSemverVersion.Minor &&
+		specSemverVersion.Patch != 0 {
+		// Treat this case differently as we want it to exactly match the spec.Version,
+		// including its Patch, in the status.Version.
+		currentSemverVersion.Patch = specSemverVersion.Patch
+
+		return ptr.To(currentSemverVersion.String())
+	}
+
+	// For all the other cases it doesn't matter to have a patch version, as EKS ignores it internally.
+	// So set the current cluster.Version (this always is a major.minor version format (e.g. "1.31")) in the status.Version.
+	// Even in the event where in the spec.Version a zero patch version is specified (e.g. "1.31.0"),
+	// the call to semver.ParseTolerant on the consumer side
+	// will make sure the version with and without the trailing zero actually result in a match.
+	return clusterV
+}
+
 func (s *Service) setStatus(cluster *eks.Cluster) error {
+	// Set the current Kubernetes control plane version in the status.
+	s.scope.ControlPlane.Status.Version = computeCurrentStatusVersion(s.scope.ControlPlane.Spec.Version, cluster.Version)
+
+	// Set the current cluster status in the control plane status.
 	switch *cluster.Status {
 	case eks.ClusterStatusDeleting:
 		s.scope.ControlPlane.Status.Ready = false
@@ -168,6 +217,8 @@ func (s *Service) setStatus(cluster *eks.Cluster) error {
 	default:
 		return errors.Errorf("unexpected EKS cluster status %s", *cluster.Status)
 	}
+
+	// Persists the control plane configuration and status.
 	if err := s.scope.PatchObject(); err != nil {
 		return errors.Wrap(err, "failed to update control plane")
 	}