integrate kubelet with the systemd watchdog

feat:  add unit test

feat:  add FeatureGate for SystemdWatchdog

fix:  linter and failed tests

feat:  add SystemdWatchdog to versioned feature list yaml

cluster/gce/gci/configure-helper.sh

@@ -1658,6 +1658,7 @@ After=network-online.target
 [Service]
 Restart=always
 RestartSec=10
+WatchdogSec=30s
 EnvironmentFile=${kubelet_env_file}
 ExecStart=${kubelet_bin} \$KUBELET_OPTS
 

pkg/features/kube_features.go

@@ -749,6 +749,16 @@ const (
 	//
 	// Enables the image volume source.
 	ImageVolume featuregate.Feature = "ImageVolume"
+
+	// owner: @zhifei92
+	// beta: v1.32
+	//
+	// Enables the systemd watchdog for the kubelet. When enabled, the kubelet will
+	// periodically notify the systemd watchdog to indicate that it is still alive.
+	// This can help prevent the system from restarting the kubelet if it becomes
+	// unresponsive. The feature gate is enabled by default, but should only be used
+	// if the system supports the systemd watchdog feature and has it configured properly.
+	SystemdWatchdog = featuregate.Feature("SystemdWatchdog")
 )
 
 func init() {

pkg/features/versioned_kube_features.go

@@ -696,6 +696,10 @@ var defaultVersionedKubernetesFeatureGates = map[featuregate.Feature]featuregate
 		{Version: version.MustParse("1.31"), Default: false, PreRelease: featuregate.Alpha},
 	},
 
+	SystemdWatchdog: {
+		{Version: version.MustParse("1.32"), Default: true, PreRelease: featuregate.Beta},
+	},
+
 	TopologyAwareHints: {
 		{Version: version.MustParse("1.21"), Default: false, PreRelease: featuregate.Alpha},
 		{Version: version.MustParse("1.23"), Default: false, PreRelease: featuregate.Beta},

pkg/kubelet/kubelet.go

@@ -118,6 +118,7 @@ import (
 	"k8s.io/kubernetes/pkg/kubelet/util/queue"
 	"k8s.io/kubernetes/pkg/kubelet/util/sliceutils"
 	"k8s.io/kubernetes/pkg/kubelet/volumemanager"
+	"k8s.io/kubernetes/pkg/kubelet/watchdog"
 	httpprobe "k8s.io/kubernetes/pkg/probe/http"
 	"k8s.io/kubernetes/pkg/security/apparmor"
 	"k8s.io/kubernetes/pkg/util/oom"
@@ -957,6 +958,14 @@ func NewMainKubelet(kubeCfg *kubeletconfiginternal.KubeletConfiguration,
 	// since this relies on the rest of the Kubelet having been constructed.
 	klet.setNodeStatusFuncs = klet.defaultNodeStatusFuncs()
 
+	if utilfeature.DefaultFeatureGate.Enabled(features.SystemdWatchdog) {
+		// NewHealthChecker returns an error indicating that the watchdog is configured but the configuration is incorrect,
+		// the kubelet will not be started.
+		klet.healthChecker, err = watchdog.NewHealthChecker(klet)
+		if err != nil {
+			return nil, fmt.Errorf("create health checker: %w", err)
+		}
+	}
 	return klet, nil
 }
 
@@ -1344,6 +1353,9 @@ type Kubelet struct {
 
 	// Track node startup latencies
 	nodeStartupLatencyTracker util.NodeStartupLatencyTracker
+
+	// Health check kubelet
+	healthChecker watchdog.HealthChecker
 }
 
 // ListPodStats is delegated to StatsProvider, which implements stats.Provider interface
@@ -1698,6 +1710,10 @@ func (kl *Kubelet) Run(updates <-chan kubetypes.PodUpdate) {
 		kl.eventedPleg.Start()
 	}
 
+	if utilfeature.DefaultFeatureGate.Enabled(features.SystemdWatchdog) {
+		kl.healthChecker.Start()
+	}
+
 	kl.syncLoop(ctx, updates, kl)
 }
 
@@ -2876,6 +2892,20 @@ func (kl *Kubelet) LatestLoopEntryTime() time.Time {
 	return val.(time.Time)
 }
 
+// SyncLoopHealthCheck checks if kubelet's sync loop that updates containers is working.
+func (kl *Kubelet) SyncLoopHealthCheck(req *http.Request) error {
+	duration := kl.resyncInterval * 2
+	minDuration := time.Minute * 5
+	if duration < minDuration {
+		duration = minDuration
+	}
+	enterLoopTime := kl.LatestLoopEntryTime()
+	if !enterLoopTime.IsZero() && time.Now().After(enterLoopTime.Add(duration)) {
+		return fmt.Errorf("sync Loop took longer than expected")
+	}
+	return nil
+}
+
 // updateRuntimeUp calls the container runtime status callback, initializing
 // the runtime dependent modules when the container runtime first comes up,
 // and returns an error if the status check fails.  If the status check is OK,
@@ -2935,11 +2965,6 @@ func (kl *Kubelet) BirthCry() {
 	kl.recorder.Eventf(kl.nodeRef, v1.EventTypeNormal, events.StartingKubelet, "Starting kubelet.")
 }
 
-// ResyncInterval returns the interval used for periodic syncs.
-func (kl *Kubelet) ResyncInterval() time.Duration {
-	return kl.resyncInterval
-}
-
 // ListenAndServe runs the kubelet HTTP server.
 func (kl *Kubelet) ListenAndServe(kubeCfg *kubeletconfiginternal.KubeletConfiguration, tlsOptions *server.TLSOptions,
 	auth server.AuthInterface, tp trace.TracerProvider) {

pkg/kubelet/server/server.go

@@ -265,9 +265,8 @@ type HostInterface interface {
 	CheckpointContainer(ctx context.Context, podUID types.UID, podFullName, containerName string, options *runtimeapi.CheckpointContainerRequest) error
 	GetKubeletContainerLogs(ctx context.Context, podFullName, containerName string, logOptions *v1.PodLogOptions, stdout, stderr io.Writer) error
 	ServeLogs(w http.ResponseWriter, req *http.Request)
-	ResyncInterval() time.Duration
 	GetHostname() string
-	LatestLoopEntryTime() time.Time
+	SyncLoopHealthCheck(req *http.Request) error
 	GetExec(ctx context.Context, podFullName string, podUID types.UID, containerName string, cmd []string, streamOpts remotecommandserver.Options) (*url.URL, error)
 	GetAttach(ctx context.Context, podFullName string, podUID types.UID, containerName string, streamOpts remotecommandserver.Options) (*url.URL, error)
 	GetPortForward(ctx context.Context, podName, podNamespace string, podUID types.UID, portForwardOpts portforward.V4Options) (*url.URL, error)
@@ -396,7 +395,7 @@ func (s *Server) InstallDefaultHandlers() {
 	healthz.InstallHandler(s.restfulCont,
 		healthz.PingHealthz,
 		healthz.LogHealthz,
-		healthz.NamedCheck("syncloop", s.syncLoopHealthCheck),
+		healthz.NamedCheck("syncloop", s.host.SyncLoopHealthCheck),
 	)
 
 	slis.SLIMetricsWithReset{}.Install(s.restfulCont)
@@ -678,20 +677,6 @@ func (s *Server) InstallProfilingHandler(enableProfilingLogHandler bool, enableC
 	}
 }
 
-// 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
-}
-
 // getContainerLogs handles containerLogs request against the Kubelet
 func (s *Server) getContainerLogs(request *restful.Request, response *restful.Response) {
 	podNamespace := request.PathParameter("podNamespace")

pkg/kubelet/server/server_test.go

@@ -91,10 +91,6 @@ type fakeKubelet struct {
 	streamingRuntime  streaming.Server
 }
 
-func (fk *fakeKubelet) ResyncInterval() time.Duration {
-	return fk.resyncInterval
-}
-
 func (fk *fakeKubelet) LatestLoopEntryTime() time.Time {
 	return fk.loopEntryTime
 }
@@ -154,6 +150,19 @@ func (fk *fakeKubelet) ListPodSandboxMetrics(ctx context.Context) ([]*runtimeapi
 	return nil, nil
 }
 
+func (fk *fakeKubelet) SyncLoopHealthCheck(req *http.Request) error {
+	duration := fk.resyncInterval * 2
+	minDuration := time.Minute * 5
+	if duration < minDuration {
+		duration = minDuration
+	}
+	enterLoopTime := fk.LatestLoopEntryTime()
+	if !enterLoopTime.IsZero() && time.Now().After(enterLoopTime.Add(duration)) {
+		return fmt.Errorf("sync Loop took longer than expected")
+	}
+	return nil
+}
+
 type fakeRuntime struct {
 	execFunc        func(string, []string, io.Reader, io.WriteCloser, io.WriteCloser, bool, <-chan remotecommand.TerminalSize) error
 	attachFunc      func(string, io.Reader, io.WriteCloser, io.WriteCloser, bool, <-chan remotecommand.TerminalSize) error

pkg/kubelet/watchdog/types.go

@@ -0,0 +1,29 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+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 watchdog
+
+import "net/http"
+
+// HealthChecker defines the interface of health checkers.
+type HealthChecker interface {
+	Start()
+}
+
+// syncLoopHealthChecker contains the health check method for syncLoop.
+type syncLoopHealthChecker interface {
+	SyncLoopHealthCheck(req *http.Request) error
+}

pkg/kubelet/watchdog/watchdog_linux.go

@@ -0,0 +1,158 @@
+//go:build linux
+// +build linux
+
+/*
+Copyright 2024 The Kubernetes Authors.
+
+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 watchdog
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/coreos/go-systemd/v22/daemon"
+
+	"k8s.io/apimachinery/pkg/util/wait"
+	"k8s.io/apiserver/pkg/server/healthz"
+	"k8s.io/klog/v2"
+)
+
+// WatchdogClient defines the interface for interacting with the systemd watchdog.
+type WatchdogClient interface {
+	SdWatchdogEnabled(unsetEnvironment bool) (time.Duration, error)
+	SdNotify(unsetEnvironment bool) (bool, error)
+}
+
+// DefaultWatchdogClient implements the WatchdogClient interface using the actual systemd daemon functions.
+type DefaultWatchdogClient struct{}
+
+var _ WatchdogClient = &DefaultWatchdogClient{}
+
+func (d *DefaultWatchdogClient) SdWatchdogEnabled(unsetEnvironment bool) (time.Duration, error) {
+	return daemon.SdWatchdogEnabled(unsetEnvironment)
+}
+
+func (d *DefaultWatchdogClient) SdNotify(unsetEnvironment bool) (bool, error) {
+	return daemon.SdNotify(unsetEnvironment, daemon.SdNotifyWatchdog)
+}
+
+// Option defines optional parameters for initializing the healthChecker
+// structure.
+type Option func(*healthChecker)
+
+func WithWatchdogClient(watchdog WatchdogClient) Option {
+	return func(hc *healthChecker) {
+		hc.watchdog = watchdog
+	}
+}
+
+type healthChecker struct {
+	checkers     []healthz.HealthChecker
+	retryBackoff wait.Backoff
+	interval     time.Duration
+	watchdog     WatchdogClient
+}
+
+var _ HealthChecker = &healthChecker{}
+
+const minimalNotifyInterval = time.Second
+
+// NewHealthChecker creates a new HealthChecker instance.
+// This function initializes the health checker and configures its behavior based on the status of the systemd watchdog.
+// If the watchdog is not enabled, the function returns an error.
+func NewHealthChecker(syncLoop syncLoopHealthChecker, opts ...Option) (HealthChecker, error) {
+	hc := &healthChecker{
+		watchdog: &DefaultWatchdogClient{},
+	}
+	for _, o := range opts {
+		o(hc)
+	}
+
+	// get watchdog information
+	watchdogVal, err := hc.watchdog.SdWatchdogEnabled(false)
+	if err != nil {
+		// Failed to get watchdog configuration information.
+		// This occurs when we want to start the watchdog but the configuration is incorrect,
+		// for example, the time is not configured correctly.
+		return nil, fmt.Errorf("configure watchdog: %w", err)
+	}
+	if watchdogVal == 0 {
+		klog.InfoS("Systemd watchdog is not enabled")
+		return &healthChecker{}, nil
+	}
+	if watchdogVal <= minimalNotifyInterval {
+		return nil, fmt.Errorf("configure watchdog timeout too small: %v", watchdogVal)
+	}
+
+	// The health checks performed by checkers are the same as those for "/healthz".
+	checkers := []healthz.HealthChecker{
+		healthz.PingHealthz,
+		healthz.LogHealthz,
+		healthz.NamedCheck("syncloop", syncLoop.SyncLoopHealthCheck),
+	}
+	retryBackoff := wait.Backoff{
+		Duration: time.Second,
+		Factor:   2.0,
+		Jitter:   0.1,
+		Steps:    2,
+	}
+	hc.checkers = checkers
+	hc.retryBackoff = retryBackoff
+	hc.interval = watchdogVal / 2
+
+	return hc, nil
+}
+
+func (hc *healthChecker) Start() {
+	if hc.interval <= 0 {
+		klog.InfoS("Systemd watchdog is not enabled or the interval is invalid, so health checking will not be started.")
+		return
+	}
+	klog.InfoS("Starting systemd watchdog with interval", "interval", hc.interval)
+
+	go wait.Forever(func() {
+		if err := hc.doCheck(); err != nil {
+			klog.ErrorS(err, "Do not notify watchdog this iteration as the kubelet is reportedly not healthy")
+			return
+		}
+
+		err := wait.ExponentialBackoff(hc.retryBackoff, func() (bool, error) {
+			ack, err := hc.watchdog.SdNotify(false)
+			if err != nil {
+				klog.V(5).InfoS("Failed to notify systemd watchdog, retrying", "error", err)
+				return false, nil
+			}
+			if !ack {
+				return false, fmt.Errorf("failed to notify systemd watchdog, notification not supported - (i.e. NOTIFY_SOCKET is unset)")
+			}
+
+			klog.V(5).InfoS("Watchdog plugin notified", "acknowledgment", ack, "state", daemon.SdNotifyWatchdog)
+			return true, nil
+		})
+		if err != nil {
+			klog.ErrorS(err, "Failed to notify watchdog")
+		}
+	}, hc.interval)
+}
+
+func (hc *healthChecker) doCheck() error {
+	for _, hc := range hc.checkers {
+		if err := hc.Check(nil); err != nil {
+			return fmt.Errorf("checker %s failed: %w", hc.Name(), err)
+		}
+	}
+	return nil
+}

pkg/kubelet/watchdog/watchdog_linux_test.go

@@ -0,0 +1,180 @@
+//go:build linux
+// +build linux
+
+/*
+Copyright 2024 The Kubernetes Authors.
+
+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 watchdog
+
+import (
+	"bytes"
+	"errors"
+	"flag"
+	"net/http"
+	"strings"
+	"testing"
+	"time"
+
+	"k8s.io/klog/v2"
+)
+
+// Mock syncLoopHealthChecker
+type mockSyncLoopHealthChecker struct {
+	healthCheckErr error
+}
+
+func (m *mockSyncLoopHealthChecker) SyncLoopHealthCheck(req *http.Request) error {
+	return m.healthCheckErr
+}
+
+// Mock WatchdogClient
+type mockWatchdogClient struct {
+	enabledVal time.Duration
+	enabledErr error
+	notifyAck  bool
+	notifyErr  error
+}
+
+func (m *mockWatchdogClient) SdWatchdogEnabled(unsetEnvironment bool) (time.Duration, error) {
+	return m.enabledVal, m.enabledErr
+}
+
+func (m *mockWatchdogClient) SdNotify(unsetEnvironment bool) (bool, error) {
+	return m.notifyAck, m.notifyErr
+}
+
+const (
+	interval      = 4 * time.Second
+	intervalSmall = 1 * time.Second
+)
+
+// TestNewHealthChecker tests the NewHealthChecker function.
+func TestNewHealthChecker(t *testing.T) {
+	// Test cases
+	tests := []struct {
+		name        string
+		mockEnabled time.Duration
+		mockErr     error
+		wantErr     bool
+	}{
+		{"Watchdog enabled", interval, nil, false},
+		{"Watchdog not enabled", 0, nil, false},
+		{"Watchdog enabled with error", interval, errors.New("mock error"), true},
+		{"Watchdog timeout too small", intervalSmall, nil, true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			mockClient := &mockWatchdogClient{
+				enabledVal: tt.mockEnabled,
+				enabledErr: tt.mockErr,
+			}
+
+			_, err := NewHealthChecker(&mockSyncLoopHealthChecker{}, WithWatchdogClient(mockClient))
+			if (err != nil) != tt.wantErr {
+				t.Errorf("NewHealthChecker() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+// TestHealthCheckerStart tests the Start method of the healthChecker.
+func TestHealthCheckerStart(t *testing.T) {
+	// Test cases
+	tests := []struct {
+		name           string
+		enabledVal     time.Duration
+		healthCheckErr error
+		notifyAck      bool
+		notifyErr      error
+		expectedLogs   []string
+	}{
+		{
+			name:           "Watchdog enabled and notify succeeds",
+			enabledVal:     interval,
+			healthCheckErr: nil,
+			notifyAck:      true,
+			notifyErr:      nil,
+			expectedLogs:   []string{"Starting systemd watchdog with interval", "Watchdog plugin notified"},
+		},
+		{
+			name:           "Watchdog enabled and notify fails, notification not supported",
+			enabledVal:     interval,
+			healthCheckErr: nil,
+			notifyAck:      false,
+			notifyErr:      nil,
+			expectedLogs:   []string{"Starting systemd watchdog with interval", "Failed to notify watchdog", "notification not supported"},
+		},
+		{
+			name:           "Watchdog enabled and notify fails, transmission failed",
+			enabledVal:     interval,
+			healthCheckErr: nil,
+			notifyAck:      false,
+			notifyErr:      errors.New("mock notify error"),
+			expectedLogs:   []string{"Starting systemd watchdog with interval", "Failed to notify watchdog"},
+		},
+		{
+			name:           "Watchdog enabled and health check fails",
+			enabledVal:     interval,
+			healthCheckErr: errors.New("mock healthy error"),
+			notifyAck:      true,
+			notifyErr:      nil,
+			expectedLogs:   []string{"Starting systemd watchdog with interval", "Do not notify watchdog this iteration as the kubelet is reportedly not healthy"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Capture logs
+			var logBuffer bytes.Buffer
+			flags := &flag.FlagSet{}
+			klog.InitFlags(flags)
+			if err := flags.Set("v", "5"); err != nil {
+				t.Fatal(err)
+			}
+			klog.LogToStderr(false)
+			klog.SetOutput(&logBuffer)
+
+			// Mock SdWatchdogEnabled to return a valid value
+			mockClient := &mockWatchdogClient{
+				enabledVal: tt.enabledVal,
+				notifyAck:  tt.notifyAck,
+				notifyErr:  tt.notifyErr,
+			}
+
+			// Create a healthChecker
+			hc, err := NewHealthChecker(&mockSyncLoopHealthChecker{healthCheckErr: tt.healthCheckErr}, WithWatchdogClient(mockClient))
+			if err != nil {
+				t.Fatalf("NewHealthChecker() failed: %v", err)
+			}
+
+			// Start the health checker
+			hc.Start()
+
+			// Wait for a short period to allow the health check to run
+			time.Sleep(2 * interval)
+
+			// Check logs to verify the health check ran
+			klog.Flush()
+			logs := logBuffer.String()
+			for _, expectedLog := range tt.expectedLogs {
+				if !strings.Contains(logs, expectedLog) {
+					t.Errorf("Expected log '%s' not found in logs: %s", expectedLog, logs)
+				}
+			}
+		})
+	}
+}

pkg/kubelet/watchdog/watchdog_unsupported.go

@@ -0,0 +1,33 @@
+//go:build !linux
+// +build !linux
+
+/*
+Copyright 2024 The Kubernetes Authors.
+
+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 watchdog
+
+type healthCheckerUnsupported struct{}
+
+var _ HealthChecker = &healthCheckerUnsupported{}
+
+// NewHealthChecker creates a fake one here
+func NewHealthChecker(_ syncLoopHealthChecker) (HealthChecker, error) {
+	return &healthCheckerUnsupported{}, nil
+}
+
+func (ow *healthCheckerUnsupported) Start() {
+	return
+}

test/featuregates_linter/test_data/versioned_feature_list.yaml

@@ -1218,6 +1218,12 @@
     lockToDefault: false
     preRelease: Alpha
     version: "1.31"
+- name: SystemdWatchdog
+  versionedSpecs:
+  - default: true
+    lockToDefault: false
+    preRelease: Beta
+    version: "1.32"
 - name: TopologyAwareHints
   versionedSpecs:
   - default: false