Skip updating Endpoints and EndpointSlice if no relevant fields change

When comparing EndpointSubsets and Endpoints, we ignore the difference
in ResourceVersion of Pod to avoid unnecessary updates caused by Pod
updates that we don't care, e.g. annotation update.

Otherwise periodic Service resync would intensively update Endpoints or
EndpointSlice whose Pods have irrelevant change between two resyncs,
leading to delay in processing newly created Services. In a scale
cluster with thousands of such Endpoints, we observed 2 minutes of
delay when the resync happens.

pkg/controller/endpoint/endpoints_controller_test.go

@@ -319,6 +319,52 @@ func TestSyncEndpointsExistingEmptySubsets(t *testing.T) {
 	endpointsHandler.ValidateRequestCount(t, 0)
 }
 
+func TestSyncEndpointsWithPodResourceVersionUpdateOnly(t *testing.T) {
+	ns := metav1.NamespaceDefault
+	testServer, endpointsHandler := makeTestServer(t, ns)
+	defer testServer.Close()
+	pod0 := testPod(ns, 0, 1, true, ipv4only)
+	pod1 := testPod(ns, 1, 1, false, ipv4only)
+	endpoints := newController(testServer.URL, 0*time.Second)
+	endpoints.endpointsStore.Add(&v1.Endpoints{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:            "foo",
+			Namespace:       ns,
+			ResourceVersion: "1",
+		},
+		Subsets: []v1.EndpointSubset{{
+			Addresses: []v1.EndpointAddress{
+				{
+					IP:        pod0.Status.PodIPs[0].IP,
+					NodeName:  &emptyNodeName,
+					TargetRef: &v1.ObjectReference{Kind: "Pod", Name: pod0.Name, Namespace: ns, ResourceVersion: "1"},
+				},
+			},
+			NotReadyAddresses: []v1.EndpointAddress{
+				{
+					IP:        pod1.Status.PodIPs[0].IP,
+					NodeName:  &emptyNodeName,
+					TargetRef: &v1.ObjectReference{Kind: "Pod", Name: pod1.Name, Namespace: ns, ResourceVersion: "2"},
+				},
+			},
+			Ports: []v1.EndpointPort{{Port: 8080, Protocol: "TCP"}},
+		}},
+	})
+	endpoints.serviceStore.Add(&v1.Service{
+		ObjectMeta: metav1.ObjectMeta{Name: "foo", Namespace: ns},
+		Spec: v1.ServiceSpec{
+			Selector: map[string]string{"foo": "bar"},
+			Ports:    []v1.ServicePort{{Port: 80, Protocol: "TCP", TargetPort: intstr.FromInt(8080)}},
+		},
+	})
+	pod0.ResourceVersion = "3"
+	pod1.ResourceVersion = "4"
+	endpoints.podStore.Add(pod0)
+	endpoints.podStore.Add(pod1)
+	endpoints.syncService(context.TODO(), ns+"/foo")
+	endpointsHandler.ValidateRequestCount(t, 0)
+}
+
 func TestSyncEndpointsNewNoSubsets(t *testing.T) {
 	ns := metav1.NamespaceDefault
 	testServer, endpointsHandler := makeTestServer(t, ns)