Merge pull request #4368 from k8s-infra-cherrypick-robot/cherry-pick-4308-to-release-1.12

[release-1.12] Fix: DNSPrefix error on existing tenant cluster

Author: k8s-ci-robot

api/v1beta1/azuremanagedcontrolplane_default.go

@@ -19,6 +19,7 @@ package v1beta1
 import (
 	"encoding/base64"
 	"fmt"
+	"reflect"
 	"strings"
 
 	"golang.org/x/crypto/ssh"
@@ -194,7 +195,7 @@ func (m *AzureManagedControlPlane) setDefaultOIDCIssuerProfile() {
 }
 
 func (m *AzureManagedControlPlane) setDefaultDNSPrefix() {
-	if m.Spec.DNSPrefix == nil {
+	if reflect.ValueOf(m.Spec.DNSPrefix).IsZero() {
 		m.Spec.DNSPrefix = ptr.To(m.Name)
 	}
 }

api/v1beta1/azuremanagedcontrolplane_webhook.go

@@ -207,10 +207,20 @@ func (mw *azureManagedControlPlaneWebhook) ValidateUpdate(ctx context.Context, o
 		allErrs = append(allErrs, err)
 	}
 
+	oldDNSPrefix := old.Spec.DNSPrefix
+	newDNSPrefix := m.Spec.DNSPrefix
+	if reflect.ValueOf(oldDNSPrefix).IsZero() {
+		oldDNSPrefix = ptr.To(old.Name)
+	}
+
+	if reflect.ValueOf(newDNSPrefix).IsZero() {
+		newDNSPrefix = ptr.To(m.Name)
+	}
+
 	if err := webhookutils.ValidateImmutable(
 		field.NewPath("Spec", "DNSPrefix"),
-		m.Spec.DNSPrefix,
-		old.Spec.DNSPrefix,
+		oldDNSPrefix,
+		newDNSPrefix,
 	); err != nil {
 		allErrs = append(allErrs, err)
 	}