Augmented kubelet healthz with syncLoop check.

Monit uses read-only port for health monitoring.

cluster/saltbase/salt/monit/kubelet

@@ -5,7 +5,7 @@ stop program = "/etc/init.d/kubelet stop"
 if does not exist then restart
 if failed
   host 127.0.0.1
-  port 10248
+  port 10255
   protocol HTTP
   request "/healthz"
 then restart

pkg/kubelet/kubelet.go

@@ -262,6 +262,7 @@ func NewMainKubelet(
 		mounter:                        mounter,
 		configureCBR0:                  configureCBR0,
 		pods:                           pods,
+		syncLoopMonitor:                util.AtomicValue{},
 	}
 
 	if plug, err := network.InitNetworkPlugin(networkPlugins, networkPluginName, &networkHost{klet}); err != nil {
@@ -491,6 +492,9 @@ type Kubelet struct {
 
 	// Number of Pods which can be run by this Kubelet
 	pods int
+
+	// Monitor Kubelet's sync loop
+	syncLoopMonitor util.AtomicValue
 }
 
 // getRootDir returns the full path to the directory under which kubelet can
@@ -1682,41 +1686,58 @@ func (kl *Kubelet) admitPods(allPods []*api.Pod, podSyncTypes map[types.UID]Sync
 func (kl *Kubelet) syncLoop(updates <-chan PodUpdate, handler SyncHandler) {
 	glog.Info("Starting kubelet main sync loop.")
 	for {
-		if !kl.containerRuntimeUp() {
-			time.Sleep(5 * time.Second)
-			glog.Infof("Skipping pod synchronization, container runtime is not up.")
-			continue
+		kl.syncLoopIteration(updates, handler)
+	}
+}
+
+func (kl *Kubelet) syncLoopIteration(updates <-chan PodUpdate, handler SyncHandler) {
+	kl.syncLoopMonitor.Store(time.Now())
+	if !kl.containerRuntimeUp() {
+		time.Sleep(5 * time.Second)
+		glog.Infof("Skipping pod synchronization, container runtime is not up.")
+		return
+	}
+	unsyncedPod := false
+	podSyncTypes := make(map[types.UID]SyncPodType)
+	select {
+	case u, ok := <-updates:
+		if !ok {
+			glog.Errorf("Update channel is closed. Exiting the sync loop.")
+			return
 		}
-		unsyncedPod := false
-		podSyncTypes := make(map[types.UID]SyncPodType)
+		kl.podManager.UpdatePods(u, podSyncTypes)
+		unsyncedPod = true
+		kl.syncLoopMonitor.Store(time.Now())
+	case <-time.After(kl.resyncInterval):
+		glog.V(4).Infof("Periodic sync")
+	}
+	start := time.Now()
+	// If we already caught some update, try to wait for some short time
+	// to possibly batch it with other incoming updates.
+	for unsyncedPod {
 		select {
-		case u, ok := <-updates:
-			if !ok {
-				glog.Errorf("Update channel is closed. Exiting the sync loop.")
-				return
-			}
+		case u := <-updates:
 			kl.podManager.UpdatePods(u, podSyncTypes)
-			unsyncedPod = true
-		case <-time.After(kl.resyncInterval):
-			glog.V(4).Infof("Periodic sync")
-		}
-		start := time.Now()
-		// If we already caught some update, try to wait for some short time
-		// to possibly batch it with other incoming updates.
-		for unsyncedPod {
-			select {
-			case u := <-updates:
-				kl.podManager.UpdatePods(u, podSyncTypes)
-			case <-time.After(5 * time.Millisecond):
-				// Break the for loop.
-				unsyncedPod = false
-			}
-		}
-		pods, mirrorPods := kl.podManager.GetPodsAndMirrorMap()
-		if err := handler.SyncPods(pods, podSyncTypes, mirrorPods, start); err != nil {
-			glog.Errorf("Couldn't sync containers: %v", err)
+			kl.syncLoopMonitor.Store(time.Now())
+		case <-time.After(5 * time.Millisecond):
+			// Break the for loop.
+			unsyncedPod = false
 		}
 	}
+	pods, mirrorPods := kl.podManager.GetPodsAndMirrorMap()
+	kl.syncLoopMonitor.Store(time.Now())
+	if err := handler.SyncPods(pods, podSyncTypes, mirrorPods, start); err != nil {
+		glog.Errorf("Couldn't sync containers: %v", err)
+	}
+	kl.syncLoopMonitor.Store(time.Now())
+}
+
+func (kl *Kubelet) LatestLoopEntryTime() time.Time {
+	val := kl.syncLoopMonitor.Load()
+	if val == nil {
+		return time.Time{}
+	}
+	return val.(time.Time)
 }
 
 // Returns the container runtime version for this Kubelet.
@@ -2263,6 +2284,10 @@ func (kl *Kubelet) StreamingConnectionIdleTimeout() time.Duration {
 	return kl.streamingConnectionIdleTimeout
 }
 
+func (kl *Kubelet) ResyncInterval() time.Duration {
+	return kl.resyncInterval
+}
+
 // GetContainerInfo returns stats (from Cadvisor) for a container.
 func (kl *Kubelet) GetContainerInfo(podFullName string, podUID types.UID, containerName string, req *cadvisorApi.ContainerInfoRequest) (*cadvisorApi.ContainerInfo, error) {
 

pkg/kubelet/kubelet_test.go

@@ -299,6 +299,28 @@ func TestKubeletDirsCompat(t *testing.T) {
 
 var emptyPodUIDs map[types.UID]SyncPodType
 
+func TestSyncLoopTimeUpdate(t *testing.T) {
+	testKubelet := newTestKubelet(t)
+	testKubelet.fakeCadvisor.On("MachineInfo").Return(&cadvisorApi.MachineInfo{}, nil)
+	kubelet := testKubelet.kubelet
+
+	loopTime1 := kubelet.LatestLoopEntryTime()
+	if !loopTime1.IsZero() {
+		t.Errorf("Unexpected sync loop time: %s, expected 0", loopTime1)
+	}
+
+	kubelet.syncLoopIteration(make(chan PodUpdate), kubelet)
+	loopTime2 := kubelet.LatestLoopEntryTime()
+	if loopTime2.IsZero() {
+		t.Errorf("Unexpected sync loop time: 0, expected non-zero value.")
+	}
+	kubelet.syncLoopIteration(make(chan PodUpdate), kubelet)
+	loopTime3 := kubelet.LatestLoopEntryTime()
+	if !loopTime3.After(loopTime1) {
+		t.Errorf("Sync Loop Time was not updated correctly. Second update timestamp should be greater than first update timestamp")
+	}
+}
+
 func TestSyncPodsStartPod(t *testing.T) {
 	testKubelet := newTestKubelet(t)
 	testKubelet.fakeCadvisor.On("MachineInfo").Return(&cadvisorApi.MachineInfo{}, nil)

pkg/kubelet/server.go

@@ -80,14 +80,12 @@ func ListenAndServeKubeletServer(host HostInterface, address net.IP, port uint,
 // ListenAndServeKubeletReadOnlyServer initializes a server to respond to HTTP network requests on the Kubelet.
 func ListenAndServeKubeletReadOnlyServer(host HostInterface, address net.IP, port uint) {
 	glog.V(1).Infof("Starting to listen read-only on %s:%d", address, port)
-	s := &Server{host, http.NewServeMux()}
-	healthz.InstallHandler(s.mux)
-	s.mux.HandleFunc("/stats/", s.handleStats)
+	s := NewServer(host, false)
 	s.mux.Handle("/metrics", prometheus.Handler())
 
 	server := &http.Server{
 		Addr:           net.JoinHostPort(address.String(), strconv.FormatUint(uint64(port), 10)),
-		Handler:        s,
+		Handler:        &s,
 		ReadTimeout:    5 * time.Minute,
 		WriteTimeout:   5 * time.Minute,
 		MaxHeaderBytes: 1 << 20,
@@ -110,7 +108,9 @@ type HostInterface interface {
 	ServeLogs(w http.ResponseWriter, req *http.Request)
 	PortForward(name string, uid types.UID, port uint16, stream io.ReadWriteCloser) error
 	StreamingConnectionIdleTimeout() time.Duration
+	ResyncInterval() time.Duration
 	GetHostname() string
+	LatestLoopEntryTime() time.Time
 }
 
 // NewServer initializes and configures a kubelet.Server object to handle HTTP requests.
@@ -132,6 +132,7 @@ func (s *Server) InstallDefaultHandlers() {
 		healthz.PingHealthz,
 		healthz.NamedCheck("docker", s.dockerHealthCheck),
 		healthz.NamedCheck("hostname", s.hostnameHealthCheck),
+		healthz.NamedCheck("syncloop", s.syncLoopHealthCheck),
 	)
 	s.mux.HandleFunc("/pods", s.handlePods)
 	s.mux.HandleFunc("/stats/", s.handleStats)
@@ -195,6 +196,20 @@ func (s *Server) hostnameHealthCheck(req *http.Request) error {
 	return nil
 }
 
+// Checks if kubelet's sync loop  that updates containers is working.
+func (s *Server) syncLoopHealthCheck(req *http.Request) error {
+	duration := s.host.ResyncInterval() * 2
+	minDuration := time.Minute * 5
+	if duration < minDuration {
+		duration = minDuration
+	}
+	enterLoopTime := s.host.LatestLoopEntryTime()
+	if !enterLoopTime.IsZero() && time.Now().After(enterLoopTime.Add(duration)) {
+		return fmt.Errorf("Sync Loop took longer than expected.")
+	}
+	return nil
+}
+
 // handleContainerLogs handles containerLogs request against the Kubelet
 func (s *Server) handleContainerLogs(w http.ResponseWriter, req *http.Request) {
 	defer req.Body.Close()

pkg/kubelet/server_test.go

@@ -55,6 +55,16 @@ type fakeKubelet struct {
 	containerLogsFunc                  func(podFullName, containerName, tail string, follow, pervious bool, stdout, stderr io.Writer) error
 	streamingConnectionIdleTimeoutFunc func() time.Duration
 	hostnameFunc                       func() string
+	resyncInterval                     time.Duration
+	loopEntryTime                      time.Time
+}
+
+func (fk *fakeKubelet) ResyncInterval() time.Duration {
+	return fk.resyncInterval
+}
+
+func (fk *fakeKubelet) LatestLoopEntryTime() time.Time {
+	return fk.loopEntryTime
 }
 
 func (fk *fakeKubelet) GetPodByName(namespace, name string) (*api.Pod, bool) {
@@ -453,51 +463,71 @@ func TestHealthCheck(t *testing.T) {
 	}
 
 	// Test with correct hostname, Docker version
-	resp, err := http.Get(fw.testHTTPServer.URL + "/healthz")
-	if err != nil {
-		t.Fatalf("Got error GETing: %v", err)
-	}
-	defer resp.Body.Close()
-	if resp.StatusCode != http.StatusOK {
-		t.Errorf("expected status code %d, got %d", http.StatusOK, resp.StatusCode)
-	}
-	body, err := ioutil.ReadAll(resp.Body)
-	if err != nil {
-		// copying the response body did not work
-		t.Fatalf("Cannot copy resp: %#v", err)
-	}
-	result := string(body)
-	if !strings.Contains(result, "ok") {
-		t.Errorf("expected body contains ok, got %s", result)
-	}
+	assertHealthIsOk(t, fw.testHTTPServer.URL+"/healthz")
 
 	//Test with incorrect hostname
 	fw.fakeKubelet.hostnameFunc = func() string {
 		return "fake"
 	}
-	resp, err = http.Get(fw.testHTTPServer.URL + "/healthz")
-	if err != nil {
-		t.Fatalf("Got error GETing: %v", err)
-	}
-	defer resp.Body.Close()
-	if resp.StatusCode != http.StatusOK {
-		t.Errorf("expected status code %d, got %d", http.StatusOK, resp.StatusCode)
-	}
+	assertHealthIsOk(t, fw.testHTTPServer.URL+"/healthz")
 
 	//Test with old container runtime version
 	fw.fakeKubelet.containerVersionFunc = func() (kubecontainer.Version, error) {
 		return dockertools.NewVersion("1.1")
 	}
 
-	resp, err = http.Get(fw.testHTTPServer.URL + "/healthz")
+	assertHealthFails(t, fw.testHTTPServer.URL+"/healthz", http.StatusInternalServerError)
+}
+
+func assertHealthFails(t *testing.T, httpURL string, expectedErrorCode int) {
+	resp, err := http.Get(httpURL)
 	if err != nil {
 		t.Fatalf("Got error GETing: %v", err)
 	}
 	defer resp.Body.Close()
-	if resp.StatusCode != http.StatusInternalServerError {
-		t.Errorf("expected status code %d, got %d", http.StatusInternalServerError, resp.StatusCode)
+	if resp.StatusCode != expectedErrorCode {
+		t.Errorf("expected status code %d, got %d", expectedErrorCode, resp.StatusCode)
+	}
+}
+
+func TestSyncLoopCheck(t *testing.T) {
+	fw := newServerTest()
+	fw.fakeKubelet.containerVersionFunc = func() (kubecontainer.Version, error) {
+		return dockertools.NewVersion("1.15")
+	}
+	fw.fakeKubelet.hostnameFunc = func() string {
+		return "127.0.0.1"
 	}
 
+	fw.fakeKubelet.resyncInterval = time.Minute
+	fw.fakeKubelet.loopEntryTime = time.Now()
+
+	// Test with correct hostname, Docker version
+	assertHealthIsOk(t, fw.testHTTPServer.URL+"/healthz")
+
+	fw.fakeKubelet.loopEntryTime = time.Now().Add(time.Minute * -10)
+	assertHealthFails(t, fw.testHTTPServer.URL+"/healthz", http.StatusInternalServerError)
+}
+
+// returns http response status code from the HTTP GET
+func assertHealthIsOk(t *testing.T, httpURL string) {
+	resp, err := http.Get(httpURL)
+	if err != nil {
+		t.Fatalf("Got error GETing: %v", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		t.Errorf("expected status code %d, got %d", http.StatusOK, resp.StatusCode)
+	}
+	body, readErr := ioutil.ReadAll(resp.Body)
+	if readErr != nil {
+		// copying the response body did not work
+		t.Fatalf("Cannot copy resp: %#v", readErr)
+	}
+	result := string(body)
+	if !strings.Contains(result, "ok") {
+		t.Errorf("expected body contains ok, got %s", result)
+	}
 }
 
 func setPodByNameFunc(fw *serverTestFramework, namespace, pod, container string) {

pkg/util/atomic_value.go

@@ -0,0 +1,42 @@
+/*
+Copyright 2015 The Kubernetes Authors All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package util
+
+import (
+	"sync"
+)
+
+// TODO(ArtfulCoder)
+// sync/atomic/Value was added in golang 1.4
+// Once support is dropped for go 1.3, this type must be deprecated in favor of sync/atomic/Value.
+// The functions are named Load/Store to match sync/atomic/Value function names.
+type AtomicValue struct {
+	value      interface{}
+	valueMutex sync.RWMutex
+}
+
+func (at *AtomicValue) Store(val interface{}) {
+	at.valueMutex.Lock()
+	defer at.valueMutex.Unlock()
+	at.value = val
+}
+
+func (at *AtomicValue) Load() interface{} {
+	at.valueMutex.RLock()
+	defer at.valueMutex.RUnlock()
+	return at.value
+}

pkg/util/atomic_value_test.go

@@ -0,0 +1,50 @@
+/*
+Copyright 2014 The Kubernetes Authors All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package util
+
+import (
+	"testing"
+	"time"
+)
+
+func ExpectValue(t *testing.T, atomicValue *AtomicValue, expectedValue interface{}) {
+	actualValue := atomicValue.Load()
+	if actualValue != expectedValue {
+		t.Error("Expected to find %v, found %v", expectedValue, actualValue)
+	}
+	ch := make(chan interface{})
+	go func() {
+		ch <- atomicValue.Load()
+	}()
+	select {
+	case actualValue = <-ch:
+		if actualValue != expectedValue {
+			t.Error("Expected to find %v, found %v", expectedValue, actualValue)
+			return
+		}
+	case <-time.After(time.Second * 5):
+		t.Error("Value could not be read")
+		return
+	}
+}
+
+func TestAtomicValue(t *testing.T) {
+	atomicValue := &AtomicValue{}
+	ExpectValue(t, atomicValue, nil)
+	atomicValue.Store(10)
+	ExpectValue(t, atomicValue, 10)
+}