Preserve deployment and template metadata during reconcile

When running `kubectl rollout restart deployment`, Kubernetes adds the
`kubectl.kubernetes.io/restartedAt` annotation to the deployment's pod
template to trigger a rolling restart. However, Knative's reconciler was
removing this annotation by completely replacing the deployment spec,
causing new pods to be immediately terminated instead of completing the
rollout.

This change preserves externally-added metadata at both the deployment
level and template level during reconciliation:
- Deployment-level labels (was already the case) and annotations (new)
- Pod template labels and annotations (e.g., kubectl.kubernetes.io/restartedAt)

The fix uses kmeta.UnionMaps to merge desired state with existing state,
allowing external annotations/labels to take precedence while still
permitting Knative to manage its own metadata.

Changes:
- cruds.go: Added preservation of deployment and template-level metadata
- table_test.go: Added test case to verify external metadata preservation

Author: linkvt

pkg/reconciler/revision/cruds.go

@@ -71,8 +71,13 @@ func (c *Reconciler) checkAndUpdateDeployment(ctx context.Context, rev *v1.Revis
 	desiredDeployment := have.DeepCopy()
 	desiredDeployment.Spec = deployment.Spec
 
-	// Carry over new labels.
+	// Carry over new labels and annotations at deployment level.
 	desiredDeployment.Labels = kmeta.UnionMaps(deployment.Labels, desiredDeployment.Labels)
+	desiredDeployment.Annotations = kmeta.UnionMaps(deployment.Annotations, desiredDeployment.Annotations)
+
+	// Carry over template-level labels and annotations (e.g., kubectl.kubernetes.io/restartedAt from rollout restart).
+	desiredDeployment.Spec.Template.Labels = kmeta.UnionMaps(deployment.Spec.Template.Labels, have.Spec.Template.Labels)
+	desiredDeployment.Spec.Template.Annotations = kmeta.UnionMaps(deployment.Spec.Template.Annotations, have.Spec.Template.Annotations)
 
 	d, err := c.kubeclient.AppsV1().Deployments(deployment.Namespace).Update(ctx, desiredDeployment, metav1.UpdateOptions{})
 	if err != nil {

pkg/reconciler/revision/table_test.go

@@ -209,6 +209,19 @@ func TestReconcile(t *testing.T) {
 			Object: deploy(t, "foo", "fix-containers"),
 		}},
 		Key: "foo/fix-containers",
+	}, {
+		Name: "preserve external deployment and template annotations and labels",
+		Objects: []runtime.Object{
+			Revision("foo", "preserve-annotations",
+				WithLogURL, allUnknownConditions, withDefaultContainerStatuses(), WithRevisionObservedGeneration(1)),
+			pa("foo", "preserve-annotations", WithReachabilityUnknown),
+			addExternalMetadata(deploy(t, "foo", "preserve-annotations")),
+			image("foo", "preserve-annotations"),
+		},
+		WantUpdates: []clientgotesting.UpdateActionImpl{{
+			Object: addExternalMetadata(deploy(t, "foo", "preserve-annotations")),
+		}},
+		Key: "foo/preserve-annotations",
 	}, {
 		Name: "failure updating deployment",
 		// Test that we handle an error updating the deployment properly.
@@ -878,6 +891,32 @@ func changeContainers(deploy *appsv1.Deployment) *appsv1.Deployment {
 	return deploy
 }
 
+func addExternalMetadata(deploy *appsv1.Deployment) *appsv1.Deployment {
+	// Deployment-level metadata
+	if deploy.Annotations == nil {
+		deploy.Annotations = make(map[string]string)
+	}
+	deploy.Annotations["external.io/annotation"] = "external-annotation"
+
+	if deploy.Labels == nil {
+		deploy.Labels = make(map[string]string)
+	}
+	deploy.Labels["external.io/label"] = "external-label"
+
+	// Template-level metadata (e.g. from kubectl restart)
+	if deploy.Spec.Template.ObjectMeta.Annotations == nil {
+		deploy.Spec.Template.ObjectMeta.Annotations = make(map[string]string)
+	}
+	deploy.Spec.Template.ObjectMeta.Annotations["external.io/template-annotation"] = "external-annotation"
+
+	if deploy.Spec.Template.ObjectMeta.Labels == nil {
+		deploy.Spec.Template.ObjectMeta.Labels = make(map[string]string)
+	}
+	deploy.Spec.Template.ObjectMeta.Labels["external.io/template-label"] = "external-label"
+
+	return deploy
+}
+
 func withDefaultContainerStatuses() RevisionOption {
 	return func(r *v1.Revision) {
 		r.Status.ContainerStatuses = []v1.ContainerStatus{{