Make sure no op updates don't affect the resource version

staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/fieldmanager.go

@@ -127,10 +127,6 @@ func (f *FieldManager) Update(liveObj, newObj runtime.Object, manager string) (r
 		return newObj, nil
 	}
 	apiVersion := fieldpath.APIVersion(f.groupVersion.String())
-	manager, err = f.buildManagerInfo(manager, metav1.ManagedFieldsOperationUpdate)
-	if err != nil {
-		return nil, fmt.Errorf("failed to build manager identifier: %v", err)
-	}
 
 	// TODO(apelisse) use the first return value when unions are implemented
 	_, managed.Fields, err = f.updater.Update(liveObjTyped, newObjTyped, apiVersion, managed.Fields, manager)
@@ -139,8 +135,24 @@ func (f *FieldManager) Update(liveObj, newObj runtime.Object, manager string) (r
 	}
 	managed.Fields = f.stripFields(managed.Fields, manager)
 
-	// Update the time in the managedFieldsEntry for this operation
-	managed.Times[manager] = &metav1.Time{Time: time.Now().UTC()}
+	// If the current operation took any fields from anything, it means the object changed,
+	// so update the timestamp of the managedFieldsEntry and merge with any previous updates from the same manager
+	if vs, ok := managed.Fields[manager]; ok {
+		delete(managed.Fields, manager)
+
+		// Build a manager identifier which will only match previous updates from the same manager
+		manager, err = f.buildManagerInfo(manager, metav1.ManagedFieldsOperationUpdate)
+		if err != nil {
+			return nil, fmt.Errorf("failed to build manager identifier: %v", err)
+		}
+
+		managed.Times[manager] = &metav1.Time{Time: time.Now().UTC()}
+		if previous, ok := managed.Fields[manager]; ok {
+			managed.Fields[manager] = fieldpath.NewVersionedSet(vs.Set().Union(previous.Set()), vs.APIVersion(), vs.Applied())
+		} else {
+			managed.Fields[manager] = vs
+		}
+	}
 
 	if err := internal.EncodeObjectManagedFields(newObj, managed); err != nil {
 		return nil, fmt.Errorf("failed to encode managed fields: %v", err)

test/integration/apiserver/apply/apply_test.go

@@ -145,6 +145,106 @@ func TestApplyAlsoCreates(t *testing.T) {
 	}
 }
 
+// TestNoOpUpdateSameResourceVersion makes sure that PUT requests which change nothing
+// will not change the resource version (no write to etcd is done)
+func TestNoOpUpdateSameResourceVersion(t *testing.T) {
+	defer featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, genericfeatures.ServerSideApply, true)()
+
+	_, client, closeFn := setup(t)
+	defer closeFn()
+
+	podName := "no-op"
+	podResource := "pods"
+	podBytes := []byte(`{
+		"apiVersion": "v1",
+		"kind": "Pod",
+		"metadata": {
+			"name": "` + podName + `",
+			"labels": {
+				"a": "one",
+				"c": "two",
+				"b": "three"
+			}
+		},
+		"spec": {
+			"containers": [{
+				"name":  "test-container-a",
+				"image": "test-image-one"
+			},{
+				"name":  "test-container-c",
+				"image": "test-image-two"
+			},{
+				"name":  "test-container-b",
+				"image": "test-image-three"
+			}]
+		}
+	}`)
+
+	_, err := client.CoreV1().RESTClient().Post().
+		Namespace("default").
+		Resource(podResource).
+		Body(podBytes).
+		Do().
+		Get()
+	if err != nil {
+		t.Fatalf("Failed to create object: %v", err)
+	}
+
+	// Sleep for one second to make sure that the times of each update operation is different.
+	time.Sleep(1 * time.Second)
+
+	createdObject, err := client.CoreV1().RESTClient().Get().Namespace("default").Resource(podResource).Name(podName).Do().Get()
+	if err != nil {
+		t.Fatalf("Failed to retrieve created object: %v", err)
+	}
+
+	createdAccessor, err := meta.Accessor(createdObject)
+	if err != nil {
+		t.Fatalf("Failed to get meta accessor for created object: %v", err)
+	}
+
+	createdBytes, err := json.MarshalIndent(createdObject, "\t", "\t")
+	if err != nil {
+		t.Fatalf("Failed to marshal created object: %v", err)
+	}
+
+	// Test that we can put the same object and don't change the RV
+	_, err = client.CoreV1().RESTClient().Put().
+		Namespace("default").
+		Resource(podResource).
+		Name(podName).
+		Body(createdBytes).
+		Do().
+		Get()
+	if err != nil {
+		t.Fatalf("Failed to apply no-op update: %v", err)
+	}
+
+	updatedObject, err := client.CoreV1().RESTClient().Get().Namespace("default").Resource(podResource).Name(podName).Do().Get()
+	if err != nil {
+		t.Fatalf("Failed to retrieve updated object: %v", err)
+	}
+
+	updatedAccessor, err := meta.Accessor(updatedObject)
+	if err != nil {
+		t.Fatalf("Failed to get meta accessor for updated object: %v", err)
+	}
+
+	updatedBytes, err := json.MarshalIndent(updatedObject, "\t", "\t")
+	if err != nil {
+		t.Fatalf("Failed to marshal updated object: %v", err)
+	}
+
+	if createdAccessor.GetResourceVersion() != updatedAccessor.GetResourceVersion() {
+		t.Fatalf("Expected same resource version to be %v but got: %v\nold object:\n%v\nnew object:\n%v",
+			createdAccessor.GetResourceVersion(),
+			updatedAccessor.GetResourceVersion(),
+			string(createdBytes),
+			string(updatedBytes),
+		)
+	}
+}
+
 // TestCreateOnApplyFailsWithUID makes sure that PATCH requests with the apply content type
 // will not create the object if it doesn't already exist and it specifies a UID
 func TestCreateOnApplyFailsWithUID(t *testing.T) {