use Watch for single object instead of WatchList

pkg/registry/generic/etcd/etcd.go

@@ -429,18 +429,7 @@ func (e *Etcd) WatchPredicate(ctx api.Context, m generic.Matcher, resourceVersio
 		return nil, err
 	}
 
-	var watchKey string
-	if name, ok := m.MatchesSingle(); ok {
-		key, err := e.KeyFunc(ctx, name)
-		if err != nil {
-			return nil, err
-		}
-		watchKey = key
-	} else {
-		watchKey = e.KeyRootFunc(ctx)
-	}
-
-	return e.Helper.WatchList(watchKey, version, func(obj runtime.Object) bool {
+	filterFunc := func(obj runtime.Object) bool {
 		matches, err := m.Matches(obj)
 		if err != nil {
 			glog.Errorf("unable to match watch: %v", err)
@@ -453,5 +442,15 @@ func (e *Etcd) WatchPredicate(ctx api.Context, m generic.Matcher, resourceVersio
 			}
 		}
 		return matches
-	})
+	}
+
+	if name, ok := m.MatchesSingle(); ok {
+		key, err := e.KeyFunc(ctx, name)
+		if err != nil {
+			return nil, err
+		}
+		return e.Helper.Watch(key, version, filterFunc)
+	}
+
+	return e.Helper.WatchList(e.KeyRootFunc(ctx), version, filterFunc)
 }

pkg/registry/generic/etcd/etcd_test.go

@@ -690,11 +690,16 @@ func TestEtcdWatch(t *testing.T) {
 
 	for name, m := range table {
 		podA := &api.Pod{
-			ObjectMeta: api.ObjectMeta{Name: "foo", ResourceVersion: "1"},
-			Spec:       api.PodSpec{Host: "machine"},
+			ObjectMeta: api.ObjectMeta{
+				Name:            "foo",
+				Namespace:       api.NamespaceDefault,
+				ResourceVersion: "1",
+			},
+			Spec: api.PodSpec{Host: "machine"},
 		}
 		respWithPodA := &etcd.Response{
 			Node: &etcd.Node{
+				Key:           "/registry/pods/default/foo",
 				Value:         runtime.EncodeOrDie(testapi.Codec(), podA),
 				ModifiedIndex: 1,
 				CreatedIndex:  1,