Merge pull request #18172 from Random-Liu/generate-sync-event

Auto commit by PR queue bot

pkg/kubelet/container/runtime.go

@@ -17,7 +17,6 @@ limitations under the License.
 package container
 
 import (
-	"errors"
 	"fmt"
 	"io"
 	"reflect"
@@ -31,32 +30,6 @@ import (
 	"k8s.io/kubernetes/pkg/volume"
 )
 
-// Container Terminated and Kubelet is backing off the restart
-var ErrCrashLoopBackOff = errors.New("CrashLoopBackOff")
-
-var (
-	// Container image pull failed, kubelet is backing off image pull
-	ErrImagePullBackOff = errors.New("ImagePullBackOff")
-
-	// Unable to inspect image
-	ErrImageInspect = errors.New("ImageInspectError")
-
-	// General image pull error
-	ErrImagePull = errors.New("ErrImagePull")
-
-	// Required Image is absent on host and PullPolicy is NeverPullImage
-	ErrImageNeverPull = errors.New("ErrImageNeverPull")
-
-	// ErrContainerNotFound returned when a container in the given pod with the
-	// given container name was not found, amongst those managed by the kubelet.
-	ErrContainerNotFound = errors.New("no matching container")
-
-	// Get http error when pulling image from registry
-	RegistryUnavailable = errors.New("RegistryUnavailable")
-)
-
-var ErrRunContainer = errors.New("RunContainerError")
-
 type Version interface {
 	// Compare compares two versions of the runtime. On success it returns -1
 	// if the version is less than the other, 1 if it is greater than the other,

pkg/kubelet/container/sync_result.go

@@ -0,0 +1,135 @@
+/*
+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 container
+
+import (
+	"errors"
+	"fmt"
+
+	utilerrors "k8s.io/kubernetes/pkg/util/errors"
+)
+
+// TODO(random-liu): We need to better organize runtime errors for introspection.
+
+// Container Terminated and Kubelet is backing off the restart
+var ErrCrashLoopBackOff = errors.New("CrashLoopBackOff")
+
+var (
+	// Container image pull failed, kubelet is backing off image pull
+	ErrImagePullBackOff = errors.New("ImagePullBackOff")
+
+	// Unable to inspect image
+	ErrImageInspect = errors.New("ImageInspectError")
+
+	// General image pull error
+	ErrImagePull = errors.New("ErrImagePull")
+
+	// Required Image is absent on host and PullPolicy is NeverPullImage
+	ErrImageNeverPull = errors.New("ErrImageNeverPull")
+
+	// ErrContainerNotFound returned when a container in the given pod with the
+	// given container name was not found, amongst those managed by the kubelet.
+	ErrContainerNotFound = errors.New("no matching container")
+
+	// Get http error when pulling image from registry
+	RegistryUnavailable = errors.New("RegistryUnavailable")
+)
+
+var (
+	ErrRunContainer  = errors.New("RunContainerError")
+	ErrKillContainer = errors.New("KillContainerError")
+	ErrVerifyNonRoot = errors.New("VerifyNonRootError")
+)
+
+var (
+	ErrSetupNetwork    = errors.New("SetupNetworkError")
+	ErrTeardownNetwork = errors.New("TeardownNetworkError")
+)
+
+// SyncAction indicates different kind of actions in SyncPod() and KillPod(). Now there are only actions
+// about start/kill container and setup/teardown network.
+type SyncAction string
+
+const (
+	StartContainer  SyncAction = "StartContainer"
+	KillContainer   SyncAction = "KillContainer"
+	SetupNetwork    SyncAction = "SetupNetwork"
+	TeardownNetwork SyncAction = "TeardownNetwork"
+)
+
+// SyncResult is the result of sync action.
+type SyncResult struct {
+	// The associated action of the result
+	Action SyncAction
+	// The target of the action, now the target can only be:
+	//  * Container: Target should be container name
+	//  * Network: Target is useless now, we just set it as pod full name now
+	Target interface{}
+	// Brief error reason
+	Error error
+	// Human readable error reason
+	Message string
+}
+
+// NewSyncResult generates new SyncResult with specific Action and Target
+func NewSyncResult(action SyncAction, target interface{}) *SyncResult {
+	return &SyncResult{Action: action, Target: target}
+}
+
+// Fail fails the SyncResult with specific error and message
+func (r *SyncResult) Fail(err error, msg string) {
+	r.Error, r.Message = err, msg
+}
+
+// PodSyncResult is the summary result of SyncPod() and KillPod()
+type PodSyncResult struct {
+	// Result of different sync actions
+	SyncResults []*SyncResult
+	// Error encountered in SyncPod() and KillPod() that is not already included in SyncResults
+	SyncError error
+}
+
+// AddSyncResult adds multiple SyncResult to current PodSyncResult
+func (p *PodSyncResult) AddSyncResult(result ...*SyncResult) {
+	p.SyncResults = append(p.SyncResults, result...)
+}
+
+// AddPodSyncResult merges a PodSyncResult to current one
+func (p *PodSyncResult) AddPodSyncResult(result PodSyncResult) {
+	p.AddSyncResult(result.SyncResults...)
+	p.SyncError = result.SyncError
+}
+
+// Fail fails the PodSyncResult with an error occured in SyncPod() and KillPod() itself
+func (p *PodSyncResult) Fail(err error) {
+	p.SyncError = err
+}
+
+// Error returns an error summarizing all the errors in PodSyncResult
+func (p *PodSyncResult) Error() error {
+	errlist := []error{}
+	if p.SyncError != nil {
+		errlist = append(errlist, fmt.Errorf("failed to SyncPod: %v\n", p.SyncError))
+	}
+	for _, result := range p.SyncResults {
+		if result.Error != nil {
+			errlist = append(errlist, fmt.Errorf("failed to %q for %q with %v: %q\n", result.Action, result.Target,
+				result.Error, result.Message))
+		}
+	}
+	return utilerrors.NewAggregate(errlist)
+}

pkg/kubelet/container/sync_result_test.go

@@ -0,0 +1,68 @@
+/*
+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 container
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestPodSyncResult(t *testing.T) {
+	okResults := []*SyncResult{
+		NewSyncResult(StartContainer, "container_0"),
+		NewSyncResult(SetupNetwork, "pod"),
+	}
+	errResults := []*SyncResult{
+		NewSyncResult(KillContainer, "container_1"),
+		NewSyncResult(TeardownNetwork, "pod"),
+	}
+	errResults[0].Fail(errors.New("error_0"), "message_0")
+	errResults[1].Fail(errors.New("error_1"), "message_1")
+
+	// If the PodSyncResult doesn't contain error result, it should not be error
+	result := PodSyncResult{}
+	result.AddSyncResult(okResults...)
+	if result.Error() != nil {
+		t.Errorf("PodSyncResult should not be error: %v", result)
+	}
+
+	// If the PodSyncResult contains error result, it should be error
+	result = PodSyncResult{}
+	result.AddSyncResult(okResults...)
+	result.AddSyncResult(errResults...)
+	if result.Error() == nil {
+		t.Errorf("PodSyncResult should be error: %q", result)
+	}
+
+	// If the PodSyncResult is failed, it should be error
+	result = PodSyncResult{}
+	result.AddSyncResult(okResults...)
+	result.Fail(errors.New("error"))
+	if result.Error() == nil {
+		t.Errorf("PodSyncResult should be error: %q", result)
+	}
+
+	// If the PodSyncResult is added an error PodSyncResult, it should be error
+	errResult := PodSyncResult{}
+	errResult.AddSyncResult(errResults...)
+	result = PodSyncResult{}
+	result.AddSyncResult(okResults...)
+	result.AddPodSyncResult(errResult)
+	if result.Error() == nil {
+		t.Errorf("PodSyncResult should be error: %q", result)
+	}
+}

pkg/kubelet/dockertools/manager.go

@@ -1224,16 +1224,23 @@ func (dm *DockerManager) GetContainerIP(containerID, interfaceName string) (stri
 // TODO(random-liu): After using pod status for KillPod(), we can also remove the kubernetesPodLabel, because all the needed information should have
 // been extract from new labels and stored in pod status.
 func (dm *DockerManager) KillPod(pod *api.Pod, runningPod kubecontainer.Pod) error {
-	// Send the kills in parallel since they may take a long time. Len + 1 since there
-	// can be Len errors + the networkPlugin teardown error.
-	errs := make(chan error, len(runningPod.Containers)+1)
+	result := dm.killPodWithSyncResult(pod, runningPod)
+	return result.Error()
+}
+
+// TODO(random-liu): This is just a temporary function, will be removed when we acturally add PodSyncResult
+// NOTE(random-liu): The pod passed in could be *nil* when kubelet restarted.
+func (dm *DockerManager) killPodWithSyncResult(pod *api.Pod, runningPod kubecontainer.Pod) (result kubecontainer.PodSyncResult) {
+	// Send the kills in parallel since they may take a long time.
+	// There may be len(runningPod.Containers) or len(runningPod.Containers)-1 of result in the channel
+	containerResults := make(chan *kubecontainer.SyncResult, len(runningPod.Containers))
 	wg := sync.WaitGroup{}
 	var (
 		networkContainer *kubecontainer.Container
 		networkSpec      *api.Container
 	)
+	wg.Add(len(runningPod.Containers))
 	for _, container := range runningPod.Containers {
-		wg.Add(1)
 		go func(container *kubecontainer.Container) {
 			defer util.HandleCrash()
 			defer wg.Done()
@@ -1258,33 +1265,36 @@ func (dm *DockerManager) KillPod(pod *api.Pod, runningPod kubecontainer.Pod) err
 				return
 			}
 
+			killContainerResult := kubecontainer.NewSyncResult(kubecontainer.KillContainer, container.Name)
 			err := dm.KillContainerInPod(container.ID, containerSpec, pod, "Need to kill pod.")
 			if err != nil {
+				killContainerResult.Fail(kubecontainer.ErrKillContainer, err.Error())
 				glog.Errorf("Failed to delete container: %v; Skipping pod %q", err, runningPod.ID)
-				errs <- err
 			}
+			containerResults <- killContainerResult
 		}(container)
 	}
 	wg.Wait()
+	close(containerResults)
+	for containerResult := range containerResults {
+		result.AddSyncResult(containerResult)
+	}
 	if networkContainer != nil {
+		teardownNetworkResult := kubecontainer.NewSyncResult(kubecontainer.TeardownNetwork, kubecontainer.BuildPodFullName(runningPod.Name, runningPod.Namespace))
+		result.AddSyncResult(teardownNetworkResult)
 		if err := dm.networkPlugin.TearDownPod(runningPod.Namespace, runningPod.Name, kubecontainer.DockerID(networkContainer.ID.ID)); err != nil {
-			glog.Errorf("Failed tearing down the infra container: %v", err)
-			errs <- err
+			message := fmt.Sprintf("Failed to teardown network for pod %q using network plugins %q: %v", runningPod.ID, dm.networkPlugin.Name(), err)
+			teardownNetworkResult.Fail(kubecontainer.ErrTeardownNetwork, message)
+			glog.Error(message)
 		}
+		killContainerResult := kubecontainer.NewSyncResult(kubecontainer.KillContainer, networkContainer.Name)
+		result.AddSyncResult(killContainerResult)
 		if err := dm.KillContainerInPod(networkContainer.ID, networkSpec, pod, "Need to kill pod."); err != nil {
+			killContainerResult.Fail(kubecontainer.ErrKillContainer, err.Error())
 			glog.Errorf("Failed to delete container: %v; Skipping pod %q", err, runningPod.ID)
-			errs <- err
 		}
 	}
-	close(errs)
-	if len(errs) > 0 {
-		errList := []error{}
-		for err := range errs {
-			errList = append(errList, err)
-		}
-		return fmt.Errorf("failed to delete containers (%v)", errList)
-	}
-	return nil
+	return
 }
 
 // KillContainerInPod kills a container in the pod. It must be passed either a container ID or a container and pod,
@@ -1560,7 +1570,8 @@ func appendToFile(filePath, stringToAppend string) error {
 }
 
 // createPodInfraContainer starts the pod infra container for a pod. Returns the docker container ID of the newly created container.
-func (dm *DockerManager) createPodInfraContainer(pod *api.Pod) (kubecontainer.DockerID, error) {
+// If any error occurs in this function, it will return a brief error and a detailed error message.
+func (dm *DockerManager) createPodInfraContainer(pod *api.Pod) (kubecontainer.DockerID, error, string) {
 	start := time.Now()
 	defer func() {
 		metrics.ContainerManagerLatency.WithLabelValues("createPodInfraContainer").Observe(metrics.SinceInMicroseconds(start))
@@ -1592,17 +1603,17 @@ func (dm *DockerManager) createPodInfraContainer(pod *api.Pod) (kubecontainer.Do
 
 	// No pod secrets for the infra container.
 	// The message isnt needed for the Infra container
-	if err, _ := dm.imagePuller.PullImage(pod, container, nil); err != nil {
-		return "", err
+	if err, msg := dm.imagePuller.PullImage(pod, container, nil); err != nil {
+		return "", err, msg
 	}
 
 	// Currently we don't care about restart count of infra container, just set it to 0.
 	id, err := dm.runContainerInPod(pod, container, netNamespace, getIPCMode(pod), getPidMode(pod), 0)
 	if err != nil {
-		return "", err
+		return "", kubecontainer.ErrRunContainer, err.Error()
 	}
 
-	return kubecontainer.DockerID(id.ID), nil
+	return kubecontainer.DockerID(id.ID), nil, ""
 }
 
 // Structure keeping information on changes that need to happen for a pod. The semantics is as follows:
@@ -1746,7 +1757,13 @@ func (dm *DockerManager) clearReasonCache(pod *api.Pod, container *api.Container
 }
 
 // Sync the running pod to match the specified desired pod.
-func (dm *DockerManager) SyncPod(pod *api.Pod, _ api.PodStatus, podStatus *kubecontainer.PodStatus, pullSecrets []api.Secret, backOff *util.Backoff) error {
+func (dm *DockerManager) SyncPod(pod *api.Pod, apiPodStatus api.PodStatus, podStatus *kubecontainer.PodStatus, pullSecrets []api.Secret, backOff *util.Backoff) error {
+	result := dm.syncPodWithSyncResult(pod, apiPodStatus, podStatus, pullSecrets, backOff)
+	return result.Error()
+}
+
+// (random-liu) This is just a temporary function, will be removed when we acturally add PodSyncEvent
+func (dm *DockerManager) syncPodWithSyncResult(pod *api.Pod, _ api.PodStatus, podStatus *kubecontainer.PodStatus, pullSecrets []api.Secret, backOff *util.Backoff) (result kubecontainer.PodSyncResult) {
 	start := time.Now()
 	defer func() {
 		metrics.ContainerManagerLatency.WithLabelValues("SyncPod").Observe(metrics.SinceInMicroseconds(start))
@@ -1754,7 +1771,8 @@ func (dm *DockerManager) SyncPod(pod *api.Pod, _ api.PodStatus, podStatus *kubec
 
 	containerChanges, err := dm.computePodContainerChanges(pod, podStatus)
 	if err != nil {
-		return err
+		result.Fail(err)
+		return
 	}
 	glog.V(3).Infof("Got container changes for pod %q: %+v", format.Pod(pod), containerChanges)
 
@@ -1774,8 +1792,10 @@ func (dm *DockerManager) SyncPod(pod *api.Pod, _ api.PodStatus, podStatus *kubec
 
 		// Killing phase: if we want to start new infra container, or nothing is running kill everything (including infra container)
 		// TODO(random-liu): We'll use pod status directly in the future
-		if err := dm.KillPod(pod, kubecontainer.ConvertPodStatusToRunningPod(podStatus)); err != nil {
-			return err
+		killResult := dm.killPodWithSyncResult(pod, kubecontainer.ConvertPodStatusToRunningPod(podStatus))
+		result.AddPodSyncResult(killResult)
+		if killResult.Error() != nil {
+			return
 		}
 	} else {
 		// Otherwise kill any running containers in this pod which are not specified as ones to keep.
@@ -1783,8 +1803,7 @@ func (dm *DockerManager) SyncPod(pod *api.Pod, _ api.PodStatus, podStatus *kubec
 		for _, containerStatus := range runningContainerStatues {
 			_, keep := containerChanges.ContainersToKeep[kubecontainer.DockerID(containerStatus.ID.ID)]
 			if !keep {
-				// NOTE(random-liu): Just log ID or log container status here?
-				glog.V(3).Infof("Killing unwanted container %+v", containerStatus)
+				glog.V(3).Infof("Killing unwanted container %q(id=%q) for pod %q", containerStatus.Name, containerStatus.ID, format.Pod(pod))
 				// attempt to find the appropriate container policy
 				var podContainer *api.Container
 				var killMessage string
@@ -1795,9 +1814,12 @@ func (dm *DockerManager) SyncPod(pod *api.Pod, _ api.PodStatus, podStatus *kubec
 						break
 					}
 				}
+				killContainerResult := kubecontainer.NewSyncResult(kubecontainer.KillContainer, containerStatus.Name)
+				result.AddSyncResult(killContainerResult)
 				if err := dm.KillContainerInPod(containerStatus.ID, podContainer, pod, killMessage); err != nil {
-					glog.Errorf("Error killing container: %v", err)
-					return err
+					killContainerResult.Fail(kubecontainer.ErrKillContainer, err.Error())
+					glog.Errorf("Error killing container %q(id=%q) for pod %q: %v", containerStatus.Name, containerStatus.ID, format.Pod(pod), err)
+					return
 				}
 			}
 		}
@@ -1807,31 +1829,45 @@ func (dm *DockerManager) SyncPod(pod *api.Pod, _ api.PodStatus, podStatus *kubec
 	podInfraContainerID := containerChanges.InfraContainerId
 	if containerChanges.StartInfraContainer && (len(containerChanges.ContainersToStart) > 0) {
 		glog.V(4).Infof("Creating pod infra container for %q", format.Pod(pod))
-		podInfraContainerID, err = dm.createPodInfraContainer(pod)
+		startContainerResult := kubecontainer.NewSyncResult(kubecontainer.StartContainer, PodInfraContainerName)
+		result.AddSyncResult(startContainerResult)
+		var msg string
+		podInfraContainerID, err, msg = dm.createPodInfraContainer(pod)
 		if err != nil {
+			startContainerResult.Fail(err, msg)
 			glog.Errorf("Failed to create pod infra container: %v; Skipping pod %q", err, format.Pod(pod))
-			return err
+			return
 		}
 
+		setupNetworkResult := kubecontainer.NewSyncResult(kubecontainer.SetupNetwork, kubecontainer.GetPodFullName(pod))
+		result.AddSyncResult(setupNetworkResult)
 		// Call the networking plugin
 		err = dm.networkPlugin.SetUpPod(pod.Namespace, pod.Name, podInfraContainerID)
 		if err != nil {
-			message := fmt.Sprintf("Failed to setup networking for pod %q using network plugins: %v; Skipping pod", format.Pod(pod), err)
+			// TODO: (random-liu) There shouldn't be "Skipping pod" in sync result message
+			message := fmt.Sprintf("Failed to setup network for pod %q using network plugins %q: %v; Skipping pod", format.Pod(pod), dm.networkPlugin.Name(), err)
+			setupNetworkResult.Fail(kubecontainer.ErrSetupNetwork, message)
 			glog.Error(message)
+
 			// Delete infra container
+			killContainerResult := kubecontainer.NewSyncResult(kubecontainer.KillContainer, PodInfraContainerName)
+			result.AddSyncResult(killContainerResult)
 			if delErr := dm.KillContainerInPod(kubecontainer.ContainerID{
 				ID:   string(podInfraContainerID),
 				Type: "docker"}, nil, pod, message); delErr != nil {
+				killContainerResult.Fail(kubecontainer.ErrKillContainer, delErr.Error())
 				glog.Warningf("Clear infra container failed for pod %q: %v", format.Pod(pod), delErr)
 			}
-			return err
+			return
 		}
 
 		// Setup the host interface unless the pod is on the host's network (FIXME: move to networkPlugin when ready)
-		podInfraContainer, err := dm.client.InspectContainer(string(podInfraContainerID))
+		var podInfraContainer *docker.Container
+		podInfraContainer, err = dm.client.InspectContainer(string(podInfraContainerID))
 		if err != nil {
 			glog.Errorf("Failed to inspect pod infra container: %v; Skipping pod %q", err, format.Pod(pod))
-			return err
+			result.Fail(err)
+			return
 		}
 		if !(pod.Spec.SecurityContext != nil && pod.Spec.SecurityContext.HostNetwork) {
 			if err = hairpin.SetUpContainer(podInfraContainer.State.Pid, "eth0"); err != nil {
@@ -1844,28 +1880,35 @@ func (dm *DockerManager) SyncPod(pod *api.Pod, _ api.PodStatus, podStatus *kubec
 		pod.Status.PodIP = dm.determineContainerIP(pod.Name, pod.Namespace, podInfraContainer)
 	}
 
-	containersStarted := 0
 	// Start everything
 	for idx := range containerChanges.ContainersToStart {
 		container := &pod.Spec.Containers[idx]
+		startContainerResult := kubecontainer.NewSyncResult(kubecontainer.StartContainer, container.Name)
+		result.AddSyncResult(startContainerResult)
 
 		// containerChanges.StartInfraContainer causes the containers to be restarted for config reasons
 		// ignore backoff
-		if !containerChanges.StartInfraContainer && dm.doBackOff(pod, container, podStatus, backOff) {
+		if !containerChanges.StartInfraContainer {
+			isInBackOff, err, msg := dm.doBackOff(pod, container, podStatus, backOff)
+			if isInBackOff {
+				startContainerResult.Fail(err, msg)
 				glog.V(4).Infof("Backing Off restarting container %+v in pod %v", container, format.Pod(pod))
 				continue
 			}
+		}
 		glog.V(4).Infof("Creating container %+v in pod %v", container, format.Pod(pod))
 		err, msg := dm.imagePuller.PullImage(pod, container, pullSecrets)
 		if err != nil {
+			startContainerResult.Fail(err, msg)
 			dm.updateReasonCache(pod, container, err.Error(), errors.New(msg))
 			continue
 		}
 
 		if container.SecurityContext != nil && container.SecurityContext.RunAsNonRoot != nil && *container.SecurityContext.RunAsNonRoot {
 			err := dm.verifyNonRoot(container)
-			dm.updateReasonCache(pod, container, "VerifyNonRootError", err)
+			dm.updateReasonCache(pod, container, kubecontainer.ErrVerifyNonRoot.Error(), err)
 			if err != nil {
+				startContainerResult.Fail(kubecontainer.ErrVerifyNonRoot, err.Error())
 				glog.Errorf("Error running pod %q container %q: %v", format.Pod(pod), container.Name, err)
 				continue
 			}
@@ -1886,20 +1929,16 @@ func (dm *DockerManager) SyncPod(pod *api.Pod, _ api.PodStatus, podStatus *kubec
 		_, err = dm.runContainerInPod(pod, container, namespaceMode, namespaceMode, getPidMode(pod), restartCount)
 		dm.updateReasonCache(pod, container, kubecontainer.ErrRunContainer.Error(), err)
 		if err != nil {
+			startContainerResult.Fail(kubecontainer.ErrRunContainer, err.Error())
 			// TODO(bburns) : Perhaps blacklist a container after N failures?
 			glog.Errorf("Error running pod %q container %q: %v", format.Pod(pod), container.Name, err)
 			continue
 		}
-		containersStarted++
 		// Successfully started the container; clear the entry in the failure
 		// reason cache.
 		dm.clearReasonCache(pod, container)
 	}
-
-	if containersStarted != len(containerChanges.ContainersToStart) {
-		return fmt.Errorf("not all containers have started: %d != %d", containersStarted, len(containerChanges.ContainersToStart))
-	}
-	return nil
+	return
 }
 
 // verifyNonRoot returns an error if the container or image will run as the root user.
@@ -1961,7 +2000,10 @@ func getUidFromUser(id string) string {
 	return id
 }
 
-func (dm *DockerManager) doBackOff(pod *api.Pod, container *api.Container, podStatus *kubecontainer.PodStatus, backOff *util.Backoff) bool {
+// If all instances of a container are garbage collected, doBackOff will also return false, which means the container may be restarted before the
+// backoff deadline. However, because that won't cause error and the chance is really slim, we can just ignore it for now.
+// If a container is still in backoff, the function will return a brief backoff error and a detailed error message.
+func (dm *DockerManager) doBackOff(pod *api.Pod, container *api.Container, podStatus *kubecontainer.PodStatus, backOff *util.Backoff) (bool, error, string) {
 	containerStatus := podStatus.FindContainerStatusByName(container.Name)
 	if containerStatus != nil && containerStatus.State == kubecontainer.ContainerStateExited && !containerStatus.FinishedAt.IsZero() {
 		ts := containerStatus.FinishedAt
@@ -1979,13 +2021,13 @@ func (dm *DockerManager) doBackOff(pod *api.Pod, container *api.Container, podSt
 			err := fmt.Errorf("Back-off %s restarting failed container=%s pod=%s", backOff.Get(stableName), container.Name, format.Pod(pod))
 			dm.updateReasonCache(pod, container, kubecontainer.ErrCrashLoopBackOff.Error(), err)
 			glog.Infof("%s", err.Error())
-			return true
+			return true, kubecontainer.ErrCrashLoopBackOff, err.Error()
 		}
 		backOff.Next(stableName, ts)
 
 	}
 	dm.clearReasonCache(pod, container)
-	return false
+	return false, nil, ""
 }
 
 // getPidMode returns the pid mode to use on the docker container based on pod.Spec.HostPID.