leaderelection: optimistically update leader lock

Signed-off-by: Eric Lin <exlin@google.com>

staging/src/k8s.io/client-go/tools/leaderelection/leaderelection.go

@@ -325,7 +325,22 @@ func (le *LeaderElector) tryAcquireOrRenew(ctx context.Context) bool {
 		AcquireTime:          now,
 	}
 
-	// 1. obtain or create the ElectionRecord
+	// 1. fast path for the leader to update optimistically assuming that the record observed
+	// last time is the current version.
+	if le.IsLeader() && le.isLeaseValid(now.Time) {
+		oldObservedRecord := le.getObservedRecord()
+		leaderElectionRecord.AcquireTime = oldObservedRecord.AcquireTime
+		leaderElectionRecord.LeaderTransitions = oldObservedRecord.LeaderTransitions
+
+		err := le.config.Lock.Update(ctx, leaderElectionRecord)
+		if err == nil {
+			le.setObservedRecord(&leaderElectionRecord)
+			return true
+		}
+		klog.Errorf("Failed to update lock optimitically: %v, falling back to slow path", err)
+	}
+
+	// 2. obtain or create the ElectionRecord
 	oldLeaderElectionRecord, oldLeaderElectionRawRecord, err := le.config.Lock.Get(ctx)
 	if err != nil {
 		if !errors.IsNotFound(err) {
@@ -342,24 +357,23 @@ func (le *LeaderElector) tryAcquireOrRenew(ctx context.Context) bool {
 		return true
 	}
 
-	// 2. Record obtained, check the Identity & Time
+	// 3. Record obtained, check the Identity & Time
 	if !bytes.Equal(le.observedRawRecord, oldLeaderElectionRawRecord) {
 		le.setObservedRecord(oldLeaderElectionRecord)
 
 		le.observedRawRecord = oldLeaderElectionRawRecord
 	}
-	if len(oldLeaderElectionRecord.HolderIdentity) > 0 &&
-		le.observedTime.Add(time.Second*time.Duration(oldLeaderElectionRecord.LeaseDurationSeconds)).After(now.Time) &&
-		!le.IsLeader() {
+	if len(oldLeaderElectionRecord.HolderIdentity) > 0 && le.isLeaseValid(now.Time) && !le.IsLeader() {
 		klog.V(4).Infof("lock is held by %v and has not yet expired", oldLeaderElectionRecord.HolderIdentity)
 		return false
 	}
 
-	// 3. We're going to try to update. The leaderElectionRecord is set to it's default
+	// 4. We're going to try to update. The leaderElectionRecord is set to it's default
 	// here. Let's correct it before updating.
 	if le.IsLeader() {
 		leaderElectionRecord.AcquireTime = oldLeaderElectionRecord.AcquireTime
 		leaderElectionRecord.LeaderTransitions = oldLeaderElectionRecord.LeaderTransitions
+		le.metrics.slowpathExercised(le.config.Name)
 	} else {
 		leaderElectionRecord.LeaderTransitions = oldLeaderElectionRecord.LeaderTransitions + 1
 	}
@@ -400,6 +414,10 @@ func (le *LeaderElector) Check(maxTolerableExpiredLease time.Duration) error {
 	return nil
 }
 
+func (le *LeaderElector) isLeaseValid(now time.Time) bool {
+	return le.observedTime.Add(time.Second * time.Duration(le.getObservedRecord().LeaseDurationSeconds)).After(now)
+}
+
 // setObservedRecord will set a new observedRecord and update observedTime to the current time.
 // Protect critical sections with lock.
 func (le *LeaderElector) setObservedRecord(observedRecord *rl.LeaderElectionRecord) {

staging/src/k8s.io/client-go/tools/leaderelection/leaderelection_test.go

@@ -610,14 +610,18 @@ func testReleaseOnCancellation(t *testing.T, objectType string) {
 					objectType: objectType,
 					reaction: func(action fakeclient.Action) (handled bool, ret runtime.Object, err error) {
 						updates++
+						// Skip initial two fast path renews
+						if updates%2 == 1 && updates < 5 {
+							return true, nil, context.Canceled
+						}
 
 						// Second update (first renew) should return our canceled error
 						// FakeClient doesn't do anything with the context so we're doing this ourselves
-						if updates == 2 {
+						if updates == 4 {
 							close(onRenewCalled)
 							<-onRenewResume
 							return true, nil, context.Canceled
-						} else if updates == 3 {
+						} else if updates == 5 {
 							// We update the lock after the cancellation to release it
 							// This wg is to avoid the data race on lockObj
 							defer wg.Done()
@@ -668,8 +672,12 @@ func testReleaseOnCancellation(t *testing.T, objectType string) {
 					objectType: objectType,
 					reaction: func(action fakeclient.Action) (handled bool, ret runtime.Object, err error) {
 						updates++
+						// Always skip fast path renew
+						if updates%2 == 1 {
+							return true, nil, context.Canceled
+						}
 						// Second update (first renew) should release the lock
-						if updates == 2 {
+						if updates == 4 {
 							// We update the lock after the cancellation to release it
 							// This wg is to avoid the data race on lockObj
 							defer wg.Done()
@@ -813,3 +821,156 @@ func assertEqualEvents(t *testing.T, expected []string, actual <-chan string) {
 		}
 	}
 }
+
+func TestFastPathLeaderElection(t *testing.T) {
+	objectType := "leases"
+	var (
+		lockObj    runtime.Object
+		updates    int
+		lockOps    []string
+		cancelFunc func()
+	)
+	resetVars := func() {
+		lockObj = nil
+		updates = 0
+		lockOps = []string{}
+		cancelFunc = nil
+	}
+	lec := LeaderElectionConfig{
+		LeaseDuration: 15 * time.Second,
+		RenewDeadline: 2 * time.Second,
+		RetryPeriod:   1 * time.Second,
+
+		Callbacks: LeaderCallbacks{
+			OnNewLeader:      func(identity string) {},
+			OnStoppedLeading: func() {},
+			OnStartedLeading: func(context.Context) {
+			},
+		},
+	}
+
+	tests := []struct {
+		name            string
+		reactors        []Reactor
+		expectedLockOps []string
+	}{
+		{
+			name: "Exercise fast path after lock acquired",
+			reactors: []Reactor{
+				{
+					verb:       "get",
+					objectType: objectType,
+					reaction: func(action fakeclient.Action) (handled bool, ret runtime.Object, err error) {
+						lockOps = append(lockOps, "get")
+						if lockObj != nil {
+							return true, lockObj, nil
+						}
+						return true, nil, errors.NewNotFound(action.(fakeclient.GetAction).GetResource().GroupResource(), action.(fakeclient.GetAction).GetName())
+					},
+				},
+				{
+					verb:       "create",
+					objectType: objectType,
+					reaction: func(action fakeclient.Action) (handled bool, ret runtime.Object, err error) {
+						lockOps = append(lockOps, "create")
+						lockObj = action.(fakeclient.CreateAction).GetObject()
+						return true, lockObj, nil
+					},
+				},
+				{
+					verb:       "update",
+					objectType: objectType,
+					reaction: func(action fakeclient.Action) (handled bool, ret runtime.Object, err error) {
+						updates++
+						lockOps = append(lockOps, "update")
+						if updates == 2 {
+							cancelFunc()
+						}
+						lockObj = action.(fakeclient.UpdateAction).GetObject()
+						return true, lockObj, nil
+					},
+				},
+			},
+			expectedLockOps: []string{"get", "create", "update", "update"},
+		},
+		{
+			name: "Fallback to slow path after fast path fails",
+			reactors: []Reactor{
+				{
+					verb:       "get",
+					objectType: objectType,
+					reaction: func(action fakeclient.Action) (handled bool, ret runtime.Object, err error) {
+						lockOps = append(lockOps, "get")
+						if lockObj != nil {
+							return true, lockObj, nil
+						}
+						return true, nil, errors.NewNotFound(action.(fakeclient.GetAction).GetResource().GroupResource(), action.(fakeclient.GetAction).GetName())
+					},
+				},
+				{
+					verb:       "create",
+					objectType: objectType,
+					reaction: func(action fakeclient.Action) (handled bool, ret runtime.Object, err error) {
+						lockOps = append(lockOps, "create")
+						lockObj = action.(fakeclient.CreateAction).GetObject()
+						return true, lockObj, nil
+					},
+				},
+				{
+					verb:       "update",
+					objectType: objectType,
+					reaction: func(action fakeclient.Action) (handled bool, ret runtime.Object, err error) {
+						updates++
+						lockOps = append(lockOps, "update")
+						switch updates {
+						case 2:
+							return true, nil, errors.NewConflict(action.(fakeclient.UpdateAction).GetResource().GroupResource(), "fake conflict", nil)
+						case 4:
+							cancelFunc()
+						}
+						lockObj = action.(fakeclient.UpdateAction).GetObject()
+						return true, lockObj, nil
+					},
+				},
+			},
+			expectedLockOps: []string{"get", "create", "update", "update", "get", "update", "update"},
+		},
+	}
+
+	for i := range tests {
+		test := &tests[i]
+		t.Run(test.name, func(t *testing.T) {
+			resetVars()
+
+			recorder := record.NewFakeRecorder(100)
+			resourceLockConfig := rl.ResourceLockConfig{
+				Identity:      "baz",
+				EventRecorder: recorder,
+			}
+			c := &fake.Clientset{}
+			for _, reactor := range test.reactors {
+				c.AddReactor(reactor.verb, objectType, reactor.reaction)
+			}
+			c.AddReactor("*", "*", func(action fakeclient.Action) (bool, runtime.Object, error) {
+				t.Errorf("unreachable action. testclient called too many times: %+v", action)
+				return true, nil, fmt.Errorf("unreachable action")
+			})
+			lock, err := rl.New("leases", "foo", "bar", c.CoreV1(), c.CoordinationV1(), resourceLockConfig)
+			if err != nil {
+				t.Fatal("resourcelock.New() = ", err)
+			}
+
+			lec.Lock = lock
+			elector, err := NewLeaderElector(lec)
+			if err != nil {
+				t.Fatal("Failed to create leader elector: ", err)
+			}
+
+			ctx, cancel := context.WithCancel(context.Background())
+			cancelFunc = cancel
+
+			elector.Run(ctx)
+			assert.Equal(t, test.expectedLockOps, lockOps, "Expected lock ops %q, got %q", test.expectedLockOps, lockOps)
+		})
+	}
+}