- scheduler extenders that are capable of maintaining their own

node cache don't need to get all the information about every
  candidate node. For huge clusters, sending full node information
  of all nodes in the cluster on the wire every time a pod is scheduled
  is expensive. If the scheduler is capable of caching node information
  along with its capabilities, sending node name alone is sufficient.
  These changes provide that optimization in a backward compatible way

- removed the inadvertent signature change of Prioritize() function
- added defensive checks as suggested
-  added annotation specific test case
- updated the comments in the scheduler types
- got rid of apiVersion thats unused
- using *v1.NodeList as suggested
- backing out pod annotation update related changes made in the
  1st commit
- Adjusted the comments in types.go and v1/types.go as suggested
  in the code review

test/integration/scheduler/extender_test.go

@@ -61,9 +61,10 @@ type priorityConfig struct {
 }
 
 type Extender struct {
-	name         string
-	predicates   []fitPredicate
-	prioritizers []priorityConfig
+	name             string
+	predicates       []fitPredicate
+	prioritizers     []priorityConfig
+	nodeCacheCapable bool
 }
 
 func (e *Extender) serveHTTP(t *testing.T, w http.ResponseWriter, req *http.Request) {
@@ -81,12 +82,9 @@ func (e *Extender) serveHTTP(t *testing.T, w http.ResponseWriter, req *http.Requ
 
 	if strings.Contains(req.URL.Path, filter) {
 		resp := &schedulerapi.ExtenderFilterResult{}
-		nodes, failedNodes, err := e.Filter(&args.Pod, &args.Nodes)
+		resp, err := e.Filter(&args)
 		if err != nil {
 			resp.Error = err.Error()
-		} else {
-			resp.Nodes = *nodes
-			resp.FailedNodes = failedNodes
 		}
 
 		if err := encoder.Encode(resp); err != nil {
@@ -95,7 +93,7 @@ func (e *Extender) serveHTTP(t *testing.T, w http.ResponseWriter, req *http.Requ
 	} else if strings.Contains(req.URL.Path, prioritize) {
 		// Prioritize errors are ignored. Default k8s priorities or another extender's
 		// priorities may be applied.
-		priorities, _ := e.Prioritize(&args.Pod, &args.Nodes)
+		priorities, _ := e.Prioritize(&args)
 
 		if err := encoder.Encode(priorities); err != nil {
 			t.Fatalf("Failed to encode %+v", priorities)
@@ -105,15 +103,21 @@ func (e *Extender) serveHTTP(t *testing.T, w http.ResponseWriter, req *http.Requ
 	}
 }
 
-func (e *Extender) Filter(pod *v1.Pod, nodes *v1.NodeList) (*v1.NodeList, schedulerapi.FailedNodesMap, error) {
-	filtered := []v1.Node{}
+func (e *Extender) filterUsingNodeCache(args *schedulerapi.ExtenderArgs) (*schedulerapi.ExtenderFilterResult, error) {
+	nodeSlice := make([]string, 0)
 	failedNodesMap := schedulerapi.FailedNodesMap{}
-	for _, node := range nodes.Items {
+	for _, nodeName := range *args.NodeNames {
 		fits := true
 		for _, predicate := range e.predicates {
-			fit, err := predicate(pod, &node)
+			fit, err := predicate(&args.Pod,
+				&v1.Node{ObjectMeta: metav1.ObjectMeta{Name: nodeName}})
 			if err != nil {
-				return &v1.NodeList{}, schedulerapi.FailedNodesMap{}, err
+				return &schedulerapi.ExtenderFilterResult{
+					Nodes:       nil,
+					NodeNames:   nil,
+					FailedNodes: schedulerapi.FailedNodesMap{},
+					Error:       err.Error(),
+				}, err
 			}
 			if !fit {
 				fits = false
@@ -121,24 +125,78 @@ func (e *Extender) Filter(pod *v1.Pod, nodes *v1.NodeList) (*v1.NodeList, schedu
 			}
 		}
 		if fits {
-			filtered = append(filtered, node)
+			nodeSlice = append(nodeSlice, nodeName)
 		} else {
-			failedNodesMap[node.Name] = fmt.Sprintf("extender failed: %s", e.name)
+			failedNodesMap[nodeName] = fmt.Sprintf("extender failed: %s", e.name)
 		}
 	}
-	return &v1.NodeList{Items: filtered}, failedNodesMap, nil
+
+	return &schedulerapi.ExtenderFilterResult{
+		Nodes:       nil,
+		NodeNames:   &nodeSlice,
+		FailedNodes: failedNodesMap,
+	}, nil
 }
 
-func (e *Extender) Prioritize(pod *v1.Pod, nodes *v1.NodeList) (*schedulerapi.HostPriorityList, error) {
+func (e *Extender) Filter(args *schedulerapi.ExtenderArgs) (*schedulerapi.ExtenderFilterResult, error) {
+	filtered := []v1.Node{}
+	failedNodesMap := schedulerapi.FailedNodesMap{}
+
+	if e.nodeCacheCapable {
+		return e.filterUsingNodeCache(args)
+	} else {
+		for _, node := range args.Nodes.Items {
+			fits := true
+			for _, predicate := range e.predicates {
+				fit, err := predicate(&args.Pod, &node)
+				if err != nil {
+					return &schedulerapi.ExtenderFilterResult{
+						Nodes:       &v1.NodeList{},
+						NodeNames:   nil,
+						FailedNodes: schedulerapi.FailedNodesMap{},
+						Error:       err.Error(),
+					}, err
+				}
+				if !fit {
+					fits = false
+					break
+				}
+			}
+			if fits {
+				filtered = append(filtered, node)
+			} else {
+				failedNodesMap[node.Name] = fmt.Sprintf("extender failed: %s", e.name)
+			}
+		}
+
+		return &schedulerapi.ExtenderFilterResult{
+			Nodes:       &v1.NodeList{Items: filtered},
+			NodeNames:   nil,
+			FailedNodes: failedNodesMap,
+		}, nil
+	}
+}
+
+func (e *Extender) Prioritize(args *schedulerapi.ExtenderArgs) (*schedulerapi.HostPriorityList, error) {
 	result := schedulerapi.HostPriorityList{}
 	combinedScores := map[string]int{}
+	var nodes = &v1.NodeList{Items: []v1.Node{}}
+
+	if e.nodeCacheCapable {
+		for _, nodeName := range *args.NodeNames {
+			nodes.Items = append(nodes.Items, v1.Node{ObjectMeta: metav1.ObjectMeta{Name: nodeName}})
+		}
+	} else {
+		nodes = args.Nodes
+	}
+
 	for _, prioritizer := range e.prioritizers {
 		weight := prioritizer.weight
 		if weight == 0 {
 			continue
 		}
 		priorityFunc := prioritizer.function
-		prioritizedList, err := priorityFunc(pod, nodes)
+		prioritizedList, err := priorityFunc(&args.Pod, nodes)
 		if err != nil {
 			return &schedulerapi.HostPriorityList{}, err
 		}
@@ -219,6 +277,17 @@ func TestSchedulerExtender(t *testing.T) {
 	}))
 	defer es2.Close()
 
+	extender3 := &Extender{
+		name:             "extender3",
+		predicates:       []fitPredicate{machine_1_2_3_Predicate},
+		prioritizers:     []priorityConfig{{machine_2_Prioritizer, 5}},
+		nodeCacheCapable: true,
+	}
+	es3 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		extender3.serveHTTP(t, w, req)
+	}))
+	defer es3.Close()
+
 	policy := schedulerapi.Policy{
 		ExtenderConfigs: []schedulerapi.ExtenderConfig{
 			{
@@ -235,6 +304,14 @@ func TestSchedulerExtender(t *testing.T) {
 				Weight:         4,
 				EnableHttps:    false,
 			},
+			{
+				URLPrefix:        es3.URL,
+				FilterVerb:       filter,
+				PrioritizeVerb:   prioritize,
+				Weight:           10,
+				EnableHttps:      false,
+				NodeCacheCapable: true,
+			},
 		},
 	}
 	policy.APIVersion = api.Registry.GroupOrDie(v1.GroupName).GroupVersion.String()
@@ -299,10 +376,11 @@ func DoTestPodScheduling(ns *v1.Namespace, t *testing.T, cs clientset.Interface)
 		t.Fatalf("Failed to schedule pod: %v", err)
 	}
 
-	if myPod, err := cs.Core().Pods(ns.Name).Get(myPod.Name, metav1.GetOptions{}); err != nil {
+	myPod, err = cs.Core().Pods(ns.Name).Get(myPod.Name, metav1.GetOptions{})
+	if err != nil {
 		t.Fatalf("Failed to get pod: %v", err)
-	} else if myPod.Spec.NodeName != "machine3" {
-		t.Fatalf("Failed to schedule using extender, expected machine3, got %v", myPod.Spec.NodeName)
+	} else if myPod.Spec.NodeName != "machine2" {
+		t.Fatalf("Failed to schedule using extender, expected machine2, got %v", myPod.Spec.NodeName)
 	}
 	t.Logf("Scheduled pod using extenders")
 }