This PR is fixing issue 4437. Webhook defaulting in v0.3.15 causing a…

…n error during KCP upgrade after upgrading cluster from v0.3.x to v0.3.15. This PR is changing every field under

spec.rolloutStrategy mutable.

controlplane/kubeadm/api/v1alpha3/kubeadm_control_plane_webhook.go

@@ -139,7 +139,7 @@ func (in *KubeadmControlPlane) ValidateUpdate(old runtime.Object) error {
 		{spec, "version"},
 		{spec, "upgradeAfter"},
 		{spec, "nodeDrainTimeout"},
-		{spec, "rolloutStrategy"},
+		{spec, "rolloutStrategy", "*"},
 	}
 
 	allErrs := in.validateCommon()

controlplane/kubeadm/api/v1alpha3/kubeadm_control_plane_webhook_test.go

@@ -189,6 +189,14 @@ func TestKubeadmControlPlaneValidateUpdate(t *testing.T) {
 				Name:      "infraTemplate",
 			},
 			Replicas: pointer.Int32Ptr(1),
+			RolloutStrategy: &RolloutStrategy{
+				Type: RollingUpdateStrategyType,
+				RollingUpdate: &RollingUpdate{
+					MaxSurge: &intstr.IntOrString{
+						IntVal: 1,
+					},
+				},
+			},
 			KubeadmConfigSpec: bootstrapv1.KubeadmConfigSpec{
 				InitConfiguration: &kubeadmv1beta1.InitConfiguration{
 					LocalAPIEndpoint: kubeadmv1beta1.APIEndpoint{
@@ -242,6 +250,13 @@ func TestKubeadmControlPlaneValidateUpdate(t *testing.T) {
 		},
 	}
 
+	updateMaxSurgeVal := before.DeepCopy()
+	updateMaxSurgeVal.Spec.RolloutStrategy.RollingUpdate.MaxSurge.IntVal = int32(0)
+	updateMaxSurgeVal.Spec.Replicas = pointer.Int32Ptr(3)
+
+	wrongReplicaCountForScaleIn := before.DeepCopy()
+	wrongReplicaCountForScaleIn.Spec.RolloutStrategy.RollingUpdate.MaxSurge.IntVal = int32(0)
+
 	invalidUpdateKubeadmConfigInit := before.DeepCopy()
 	invalidUpdateKubeadmConfigInit.Spec.KubeadmConfigSpec.InitConfiguration = &kubeadmv1beta1.InitConfiguration{}
 
@@ -745,6 +760,18 @@ func TestKubeadmControlPlaneValidateUpdate(t *testing.T) {
 			before:    disallowedUpgrade118Prev,
 			kcp:       disallowedUpgrade119Version,
 		},
+		{
+			name:      "should not return an error when maxSurge value is updated to 0",
+			expectErr: false,
+			before:    before,
+			kcp:       updateMaxSurgeVal,
+		},
+		{
+			name:      "should return an error when maxSurge value is updated to 0, but replica count is < 3",
+			expectErr: true,
+			before:    before,
+			kcp:       wrongReplicaCountForScaleIn,
+		},
 	}
 
 	for _, tt := range tests {
@@ -761,6 +788,56 @@ func TestKubeadmControlPlaneValidateUpdate(t *testing.T) {
 	}
 }
 
+func TestKubeadmControlPlaneValidateUpdateAfterDefaulting(t *testing.T) {
+	before := &KubeadmControlPlane{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "test",
+			Namespace: "foo",
+		},
+		Spec: KubeadmControlPlaneSpec{
+			Version: "v1.19.0",
+			InfrastructureTemplate: corev1.ObjectReference{
+				Namespace: "foo",
+				Name:      "infraTemplate",
+			},
+		},
+	}
+
+	afterDefault := before.DeepCopy()
+	afterDefault.Default()
+
+	tests := []struct {
+		name      string
+		expectErr bool
+		before    *KubeadmControlPlane
+		kcp       *KubeadmControlPlane
+	}{
+		{
+			name:      "update should succeed after defaulting",
+			expectErr: false,
+			before:    before,
+			kcp:       afterDefault,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			g := NewWithT(t)
+			err := tt.kcp.ValidateUpdate(tt.before.DeepCopy())
+			if tt.expectErr {
+				g.Expect(err).To(HaveOccurred())
+			} else {
+				g.Expect(err).To(Succeed())
+				g.Expect(tt.kcp.Spec.InfrastructureTemplate.Namespace).To(Equal(tt.before.Namespace))
+				g.Expect(tt.kcp.Spec.Version).To(Equal("v1.19.0"))
+				g.Expect(tt.kcp.Spec.RolloutStrategy.Type).To(Equal(RollingUpdateStrategyType))
+				g.Expect(tt.kcp.Spec.RolloutStrategy.RollingUpdate.MaxSurge.IntVal).To(Equal(int32(1)))
+				g.Expect(tt.kcp.Spec.Replicas).To(Equal(pointer.Int32Ptr(1)))
+			}
+		})
+	}
+}
+
 func TestPathsMatch(t *testing.T) {
 	tests := []struct {
 		name          string