kubelet源码分析（五）之 syncPod

以下代码分析基于 kubernetes v1.12.0 版本。

本文主要分析kubelet中syncPod的部分。

1. managePodLoop

managePodLoop通过读取podUpdateschannel的信息，执行syncPodFn函数，而syncPodFn函数在newPodWorkers的时候赋值了，即kubelet.syncPod。

managePodLoop完整代码如下：

此部分代码位于pkg/kubelet/pod_workers.go

  1. func (p *podWorkers) managePodLoop(podUpdates <-chan UpdatePodOptions) {
  2.     var lastSyncTime time.Time
  3.     for update := range podUpdates {
  4.         err := func() error {
  5.             podUID := update.Pod.UID
  6.             // This is a blocking call that would return only if the cache
  7.             // has an entry for the pod that is newer than minRuntimeCache
  8.             // Time. This ensures the worker doesn't start syncing until
  9.             // after the cache is at least newer than the finished time of
  10.             // the previous sync.
  11.             status, err := p.podCache.GetNewerThan(podUID, lastSyncTime)
  12.             if err != nil {
  13.                 // This is the legacy event thrown by manage pod loop
  14.                 // all other events are now dispatched from syncPodFn
  15.                 p.recorder.Eventf(update.Pod, v1.EventTypeWarning, events.FailedSync, "error determining status: %v", err)
  16.                 return err
  17.             }
  18.       // 该部分的syncPodFn实际上的实现函数是kubelet.syncPod
  19.             err = p.syncPodFn(syncPodOptions{
  20.                 mirrorPod:      update.MirrorPod,
  21.                 pod:            update.Pod,
  22.                 podStatus:      status,
  23.                 killPodOptions: update.KillPodOptions,
  24.                 updateType:     update.UpdateType,
  25.             })
  26.             lastSyncTime = time.Now()
  27.             return err
  28.         }()
  29.         // notify the call-back function if the operation succeeded or not
  30.         if update.OnCompleteFunc != nil {
  31.             update.OnCompleteFunc(err)
  32.         }
  33.         if err != nil {
  34.             // IMPORTANT: we do not log errors here, the syncPodFn is responsible for logging errors
  35.             glog.Errorf("Error syncing pod %s (%q), skipping: %v", update.Pod.UID, format.Pod(update.Pod), err)
  36.         }
  37.         p.wrapUp(update.Pod.UID, err)
  38.     }
  39. }

以下分析syncPod相关逻辑。

2. syncPod

syncPod可以理解为是一个单个pod进行同步任务的事务脚本。其中入参是syncPodOptions，syncPodOptions记录了需要同步的pod的相关信息。具体定义如下：

  1. // syncPodOptions provides the arguments to a SyncPod operation.
  2. type syncPodOptions struct {
  3.     // the mirror pod for the pod to sync, if it is a static pod
  4.     mirrorPod *v1.Pod
  5.     // pod to sync
  6.     pod *v1.Pod
  7.     // the type of update (create, update, sync)
  8.     updateType kubetypes.SyncPodType
  9.     // the current status
  10.     podStatus *kubecontainer.PodStatus
  11.     // if update type is kill, use the specified options to kill the pod.
  12.     killPodOptions *KillPodOptions
  13. }

syncPod主要执行以下的工作流：

  • 如果是正在创建的pod，则记录pod worker的启动latency。
  • 调用generateAPIPodStatus为pod提供v1.PodStatus信息。
  • 如果pod是第一次运行，记录pod的启动latency。
  • 更新status manager中的pod状态。
  • 如果pod不应该被运行则杀死pod。
  • 如果pod是一个static pod，并且没有对应的mirror pod，则创建一个mirror pod。
  • 如果没有pod的数据目录则给pod创建对应的数据目录。
  • 等待volume被attach或mount。
  • 获取pod的secret数据。
  • 调用container runtime的SyncPod函数，执行相关pod操作。
  • 更新pod的ingress和egress的traffic limit。

当以上任务流中有任何的error，则return error。在下一次执行syncPod的任务流会被再次执行。对于错误信息会被记录到event中，方便debug。

以下对syncPod的执行过程进行分析。

syncPod的代码位于pkg/kubelet/kubelet.go

2.1. SyncPodKill

首先，获取syncPodOptions的pod信息。

  1. func (kl *Kubelet) syncPod(o syncPodOptions) error {
  2.     // pull out the required options
  3.     pod := o.pod
  4.     mirrorPod := o.mirrorPod
  5.     podStatus := o.podStatus
  6.     updateType := o.updateType
  7.     ...
  8. }

如果pod是需要被杀死的，则执行killPod，会在指定的宽限期内杀死pod。

  1. // if we want to kill a pod, do it now!
  2. if updateType == kubetypes.SyncPodKill {
  3.     killPodOptions := o.killPodOptions
  4.     if killPodOptions == nil || killPodOptions.PodStatusFunc == nil {
  5.         return fmt.Errorf("kill pod options are required if update type is kill")
  6.     }
  7.     apiPodStatus := killPodOptions.PodStatusFunc(pod, podStatus)
  8.     kl.statusManager.SetPodStatus(pod, apiPodStatus)
  9.     // we kill the pod with the specified grace period since this is a termination
  10.     if err := kl.killPod(pod, nil, podStatus, killPodOptions.PodTerminationGracePeriodSecondsOverride); err != nil {
  11.         kl.recorder.Eventf(pod, v1.EventTypeWarning, events.FailedToKillPod, "error killing pod: %v", err)
  12.         // there was an error killing the pod, so we return that error directly
  13.         utilruntime.HandleError(err)
  14.         return err
  15.     }
  16.     return nil
  17. }

2.2. SyncPodCreate

如果pod是需要被创建的，则记录pod的启动latency，latency与pod在apiserver中第一次被记录相关。

  1. // Latency measurements for the main workflow are relative to the
  2. // first time the pod was seen by the API server.
  3. var firstSeenTime time.Time
  4. if firstSeenTimeStr, ok := pod.Annotations[kubetypes.ConfigFirstSeenAnnotationKey]; ok {
  5.     firstSeenTime = kubetypes.ConvertToTimestamp(firstSeenTimeStr).Get()
  6. }
  8. // Record pod worker start latency if being created
  9. // TODO: make pod workers record their own latencies
  10. if updateType == kubetypes.SyncPodCreate {
  11.     if !firstSeenTime.IsZero() {
  12.         // This is the first time we are syncing the pod. Record the latency
  13.         // since kubelet first saw the pod if firstSeenTime is set.
  14.         metrics.PodWorkerStartLatency.Observe(metrics.SinceInMicroseconds(firstSeenTime))
  15.     } else {
  16.         glog.V(3).Infof("First seen time not recorded for pod %q", pod.UID)
  17.     }
  18. }

通过pod和pod status生成最终的api pod status并设置pod的IP。

  1. // Generate final API pod status with pod and status manager status
  2. apiPodStatus := kl.generateAPIPodStatus(pod, podStatus)
  3. // The pod IP may be changed in generateAPIPodStatus if the pod is using host network. (See #24576)
  4. // TODO(random-liu): After writing pod spec into container labels, check whether pod is using host network, and
  5. // set pod IP to hostIP directly in runtime.GetPodStatus
  6. podStatus.IP = apiPodStatus.PodIP

记录pod到running状态的时间。

  1. // Record the time it takes for the pod to become running.
  2. existingStatus, ok := kl.statusManager.GetPodStatus(pod.UID)
  3. if !ok || existingStatus.Phase == v1.PodPending && apiPodStatus.Phase == v1.PodRunning &&
  4.     !firstSeenTime.IsZero() {
  5.     metrics.PodStartLatency.Observe(metrics.SinceInMicroseconds(firstSeenTime))
  6. }

如果pod是不可运行的，则更新pod和container的状态和相应的原因。

  1. runnable := kl.canRunPod(pod)
  2. if !runnable.Admit {
  3.     // Pod is not runnable; update the Pod and Container statuses to why.
  4.     apiPodStatus.Reason = runnable.Reason
  5.     apiPodStatus.Message = runnable.Message
  6.     // Waiting containers are not creating.
  7.     const waitingReason = "Blocked"
  8.     for _, cs := range apiPodStatus.InitContainerStatuses {
  9.         if cs.State.Waiting != nil {
  10.             cs.State.Waiting.Reason = waitingReason
  11.         }
  12.     }
  13.     for _, cs := range apiPodStatus.ContainerStatuses {
  14.         if cs.State.Waiting != nil {
  15.             cs.State.Waiting.Reason = waitingReason
  16.         }
  17.     }
  18. }

并更新status manager中的状态信息，杀死不可运行的pod。

  1. // Update status in the status manager
  2. kl.statusManager.SetPodStatus(pod, apiPodStatus)
  4. // Kill pod if it should not be running
  5. if !runnable.Admit || pod.DeletionTimestamp != nil || apiPodStatus.Phase == v1.PodFailed {
  6.     var syncErr error
  7.     if err := kl.killPod(pod, nil, podStatus, nil); err != nil {
  8.         kl.recorder.Eventf(pod, v1.EventTypeWarning, events.FailedToKillPod, "error killing pod: %v", err)
  9.         syncErr = fmt.Errorf("error killing pod: %v", err)
  10.         utilruntime.HandleError(syncErr)
  11.     } else {
  12.         if !runnable.Admit {
  13.             // There was no error killing the pod, but the pod cannot be run.
  14.             // Return an error to signal that the sync loop should back off.
  15.             syncErr = fmt.Errorf("pod cannot be run: %s", runnable.Message)
  16.         }
  17.     }
  18.     return syncErr
  19. }

如果网络插件还没到Ready状态，则只有在使用host网络模式的情况下才启动pod。

  1. // If the network plugin is not ready, only start the pod if it uses the host network
  2. if rs := kl.runtimeState.networkErrors(); len(rs) != 0 && !kubecontainer.IsHostNetworkPod(pod) {
  3.     kl.recorder.Eventf(pod, v1.EventTypeWarning, events.NetworkNotReady, "%s: %v", NetworkNotReadyErrorMsg, rs)
  4.     return fmt.Errorf("%s: %v", NetworkNotReadyErrorMsg, rs)
  5. }

2.3. Cgroups

给pod创建Cgroups，如果cgroups-per-qos参数开启，则申请相应的资源。对于terminated的pod不需要创建或更新pod的Cgroups。

当重新启动kubelet并且启用cgroups-per-qos时，应该间歇性地终止所有pod的运行容器并在qos cgroup hierarchy下重新启动。

如果pod的cgroup已经存在或者pod第一次运行，不杀死pod中容器。

  1. // Create Cgroups for the pod and apply resource parameters
  2. // to them if cgroups-per-qos flag is enabled.
  3. pcm := kl.containerManager.NewPodContainerManager()
  4. // If pod has already been terminated then we need not create
  5. // or update the pod's cgroup
  6. if !kl.podIsTerminated(pod) {
  7.     // When the kubelet is restarted with the cgroups-per-qos
  8.     // flag enabled, all the pod's running containers
  9.     // should be killed intermittently and brought back up
  10.     // under the qos cgroup hierarchy.
  11.     // Check if this is the pod's first sync
  12.     firstSync := true
  13.     for _, containerStatus := range apiPodStatus.ContainerStatuses {
  14.         if containerStatus.State.Running != nil {
  15.             firstSync = false
  16.             break
  17.         }
  18.     }
  19.     // Don't kill containers in pod if pod's cgroups already
  20.     // exists or the pod is running for the first time
  21.     podKilled := false
  22.     if !pcm.Exists(pod) && !firstSync {
  23.         if err := kl.killPod(pod, nil, podStatus, nil); err == nil {
  24.             podKilled = true
  25.         }
  26.     }
  27.     ...

如果pod被杀死并且重启策略是Never，则不创建或更新对应的Cgroups，否则创建和更新pod的Cgroups。

  1. // Create and Update pod's Cgroups
  2. // Don't create cgroups for run once pod if it was killed above
  3. // The current policy is not to restart the run once pods when
  4. // the kubelet is restarted with the new flag as run once pods are
  5. // expected to run only once and if the kubelet is restarted then
  6. // they are not expected to run again.
  7. // We don't create and apply updates to cgroup if its a run once pod and was killed above
  8. if !(podKilled && pod.Spec.RestartPolicy == v1.RestartPolicyNever) {
  9.     if !pcm.Exists(pod) {
  10.         if err := kl.containerManager.UpdateQOSCgroups(); err != nil {
  11.             glog.V(2).Infof("Failed to update QoS cgroups while syncing pod: %v", err)
  12.         }
  13.         if err := pcm.EnsureExists(pod); err != nil {
  14.             kl.recorder.Eventf(pod, v1.EventTypeWarning, events.FailedToCreatePodContainer, "unable to ensure pod container exists: %v", err)
  15.             return fmt.Errorf("failed to ensure that the pod: %v cgroups exist and are correctly applied: %v", pod.UID, err)
  16.         }
  17.     }
  18. }

其中创建Cgroups是通过containerManager的UpdateQOSCgroups来执行。

  1. if err := kl.containerManager.UpdateQOSCgroups(); err != nil {
  2.     glog.V(2).Infof("Failed to update QoS cgroups while syncing pod: %v", err)
  3. }

2.4. Mirror Pod

如果pod是一个static pod，没有对应的mirror pod，则创建一个mirror pod；如果存在mirror pod则删除再重建一个mirror pod。

  1. // Create Mirror Pod for Static Pod if it doesn't already exist
  2. if kubepod.IsStaticPod(pod) {
  3.     podFullName := kubecontainer.GetPodFullName(pod)
  4.     deleted := false
  5.     if mirrorPod != nil {
  6.         if mirrorPod.DeletionTimestamp != nil || !kl.podManager.IsMirrorPodOf(mirrorPod, pod) {
  7.             // The mirror pod is semantically different from the static pod. Remove
  8.             // it. The mirror pod will get recreated later.
  9.             glog.Warningf("Deleting mirror pod %q because it is outdated", format.Pod(mirrorPod))
  10.             if err := kl.podManager.DeleteMirrorPod(podFullName); err != nil {
  11.                 glog.Errorf("Failed deleting mirror pod %q: %v", format.Pod(mirrorPod), err)
  12.             } else {
  13.                 deleted = true
  14.             }
  15.         }
  16.     }
  17.     if mirrorPod == nil || deleted {
  18.         node, err := kl.GetNode()
  19.         if err != nil || node.DeletionTimestamp != nil {
  20.             glog.V(4).Infof("No need to create a mirror pod, since node %q has been removed from the cluster", kl.nodeName)
  21.         } else {
  22.             glog.V(4).Infof("Creating a mirror pod for static pod %q", format.Pod(pod))
  23.             if err := kl.podManager.CreateMirrorPod(pod); err != nil {
  24.                 glog.Errorf("Failed creating a mirror pod for %q: %v", format.Pod(pod), err)
  25.             }
  26.         }
  27.     }
  28. }

2.5. makePodDataDirs

给pod创建数据目录。

  1. // Make data directories for the pod
  2. if err := kl.makePodDataDirs(pod); err != nil {
  3.     kl.recorder.Eventf(pod, v1.EventTypeWarning, events.FailedToMakePodDataDirectories, "error making pod data directories: %v", err)
  4.     glog.Errorf("Unable to make pod data directories for pod %q: %v", format.Pod(pod), err)
  5.     return err
  6. }

其中数据目录包括

  • PodDir：{kubelet.rootDirectory}/pods/podUID
  • PodVolumesDir：{PodDir}/volumes
  • PodPluginsDir：{PodDir}/plugins
  1. // makePodDataDirs creates the dirs for the pod datas.
  2. func (kl *Kubelet) makePodDataDirs(pod *v1.Pod) error {
  3.     uid := pod.UID
  4.     if err := os.MkdirAll(kl.getPodDir(uid), 0750); err != nil && !os.IsExist(err) {
  5.         return err
  6.     }
  7.     if err := os.MkdirAll(kl.getPodVolumesDir(uid), 0750); err != nil && !os.IsExist(err) {
  8.         return err
  9.     }
  10.     if err := os.MkdirAll(kl.getPodPluginsDir(uid), 0750); err != nil && !os.IsExist(err) {
  11.         return err
  12.     }
  13.     return nil
  14. }

2.6. mount volumes

对非terminated状态的pod挂载volume。

  1. // Volume manager will not mount volumes for terminated pods
  2. if !kl.podIsTerminated(pod) {
  3.     // Wait for volumes to attach/mount
  4.     if err := kl.volumeManager.WaitForAttachAndMount(pod); err != nil {
  5.         kl.recorder.Eventf(pod, v1.EventTypeWarning, events.FailedMountVolume, "Unable to mount volumes for pod %q: %v", format.Pod(pod), err)
  6.         glog.Errorf("Unable to mount volumes for pod %q: %v; skipping pod", format.Pod(pod), err)
  7.         return err
  8.     }
  9. }

2.7. PullSecretsForPod

获取pod的secret数据。

  1. // Fetch the pull secrets for the pod
  2. pullSecrets := kl.getPullSecretsForPod(pod)

getPullSecretsForPod具体实现函数如下：

  1. // getPullSecretsForPod inspects the Pod and retrieves the referenced pull
  2. // secrets.
  3. func (kl *Kubelet) getPullSecretsForPod(pod *v1.Pod) []v1.Secret {
  4.     pullSecrets := []v1.Secret{}
  6.     for _, secretRef := range pod.Spec.ImagePullSecrets {
  7.         secret, err := kl.secretManager.GetSecret(pod.Namespace, secretRef.Name)
  8.         if err != nil {
  9.             glog.Warningf("Unable to retrieve pull secret %s/%s for %s/%s due to %v.  The image pull may not succeed.", pod.Namespace, secretRef.Name, pod.Namespace, pod.Name, err)
  10.             continue
  11.         }
  13.         pullSecrets = append(pullSecrets, *secret)
  14.     }
  16.     return pullSecrets
  17. }

2.8. containerRuntime.SyncPod

调用container runtime的SyncPod函数，执行相关pod操作，由此kubelet.syncPod的操作逻辑转入containerRuntime.SyncPod函数中。

  1. // Call the container runtime's SyncPod callback
  2. result := kl.containerRuntime.SyncPod(pod, apiPodStatus, podStatus, pullSecrets, kl.backOff)
  3. kl.reasonCache.Update(pod.UID, result)
  4. if err := result.Error(); err != nil {
  5.     // Do not return error if the only failures were pods in backoff
  6.     for _, r := range result.SyncResults {
  7.         if r.Error != kubecontainer.ErrCrashLoopBackOff && r.Error != images.ErrImagePullBackOff {
  8.             // Do not record an event here, as we keep all event logging for sync pod failures
  9.             // local to container runtime so we get better errors
  10.             return err
  11.         }
  12.     }
  14.     return nil
  15. }

3. Runtime.SyncPod

SyncPod主要执行sync操作使得运行的pod达到期望状态的pod。主要执行以下操作：

  • 计算sandbox和container的变化。
  • 必要的时候杀死pod。
  • 杀死所有不需要运行的container。
  • 必要时创建sandbox。
  • 创建init container。
  • 创建正常的container。

Runtime.SyncPod部分代码位于pkg/kubelet/kuberuntime/kuberuntime_manager.go

3.1. computePodActions

计算sandbox和container的变化。

  1. // Step 1: Compute sandbox and container changes.
  2. podContainerChanges := m.computePodActions(pod, podStatus)
  3. glog.V(3).Infof("computePodActions got %+v for pod %q", podContainerChanges, format.Pod(pod))
  4. if podContainerChanges.CreateSandbox {
  5.     ref, err := ref.GetReference(legacyscheme.Scheme, pod)
  6.     if err != nil {
  7.         glog.Errorf("Couldn't make a ref to pod %q: '%v'", format.Pod(pod), err)
  8.     }
  9.     if podContainerChanges.SandboxID != "" {
  10.         m.recorder.Eventf(ref, v1.EventTypeNormal, events.SandboxChanged, "Pod sandbox changed, it will be killed and re-created.")
  11.     } else {
  12.         glog.V(4).Infof("SyncPod received new pod %q, will create a sandbox for it", format.Pod(pod))
  13.     }
  14. }

3.2. killPodWithSyncResult

必要的时候杀死pod。

  1. // Step 2: Kill the pod if the sandbox has changed.
  2. if podContainerChanges.KillPod {
  3.     if !podContainerChanges.CreateSandbox {
  4.         glog.V(4).Infof("Stopping PodSandbox for %q because all other containers are dead.", format.Pod(pod))
  5.     } else {
  6.         glog.V(4).Infof("Stopping PodSandbox for %q, will start new one", format.Pod(pod))
  7.     }
  9.     killResult := m.killPodWithSyncResult(pod, kubecontainer.ConvertPodStatusToRunningPod(m.runtimeName, podStatus), nil)
  10.     result.AddPodSyncResult(killResult)
  11.     if killResult.Error() != nil {
  12.         glog.Errorf("killPodWithSyncResult failed: %v", killResult.Error())
  13.         return
  14.     }
  16.     if podContainerChanges.CreateSandbox {
  17.         m.purgeInitContainers(pod, podStatus)
  18.     }
  19. }

3.3. killContainer

杀死所有不需要运行的container。

  1. // Step 3: kill any running containers in this pod which are not to keep.
  2. for containerID, containerInfo := range podContainerChanges.ContainersToKill {
  3.     glog.V(3).Infof("Killing unwanted container %q(id=%q) for pod %q", containerInfo.name, containerID, format.Pod(pod))
  4.     killContainerResult := kubecontainer.NewSyncResult(kubecontainer.KillContainer, containerInfo.name)
  5.     result.AddSyncResult(killContainerResult)
  6.     if err := m.killContainer(pod, containerID, containerInfo.name, containerInfo.message, nil); err != nil {
  7.         killContainerResult.Fail(kubecontainer.ErrKillContainer, err.Error())
  8.         glog.Errorf("killContainer %q(id=%q) for pod %q failed: %v", containerInfo.name, containerID, format.Pod(pod), err)
  9.         return
  10.     }
  11. }

3.4. createPodSandbox

必要时创建sandbox。

  1. // Step 4: Create a sandbox for the pod if necessary.
  2. ...
  3. glog.V(4).Infof("Creating sandbox for pod %q", format.Pod(pod))
  4. createSandboxResult := kubecontainer.NewSyncResult(kubecontainer.CreatePodSandbox, format.Pod(pod))
  5. result.AddSyncResult(createSandboxResult)
  6. podSandboxID, msg, err = m.createPodSandbox(pod, podContainerChanges.Attempt)
  7. if err != nil {
  8.     createSandboxResult.Fail(kubecontainer.ErrCreatePodSandbox, msg)
  9.     glog.Errorf("createPodSandbox for pod %q failed: %v", format.Pod(pod), err)
  10.     ref, referr := ref.GetReference(legacyscheme.Scheme, pod)
  11.     if referr != nil {
  12.         glog.Errorf("Couldn't make a ref to pod %q: '%v'", format.Pod(pod), referr)
  13.     }
  14.     m.recorder.Eventf(ref, v1.EventTypeWarning, events.FailedCreatePodSandBox, "Failed create pod sandbox: %v", err)
  15.     return
  16. }
  17. glog.V(4).Infof("Created PodSandbox %q for pod %q", podSandboxID, format.Pod(pod))

3.5. start init container

创建init container。

  1. // Step 5: start the init container.
  2. if container := podContainerChanges.NextInitContainerToStart; container != nil {
  3.     // Start the next init container.
  4.     startContainerResult := kubecontainer.NewSyncResult(kubecontainer.StartContainer, container.Name)
  5.     result.AddSyncResult(startContainerResult)
  6.     isInBackOff, msg, err := m.doBackOff(pod, container, podStatus, backOff)
  7.     if isInBackOff {
  8.         startContainerResult.Fail(err, msg)
  9.         glog.V(4).Infof("Backing Off restarting init container %+v in pod %v", container, format.Pod(pod))
  10.         return
  11.     }
  13.     glog.V(4).Infof("Creating init container %+v in pod %v", container, format.Pod(pod))
  14.     if msg, err := m.startContainer(podSandboxID, podSandboxConfig, container, pod, podStatus, pullSecrets, podIP, kubecontainer.ContainerTypeInit); err != nil {
  15.         startContainerResult.Fail(err, msg)
  16.         utilruntime.HandleError(fmt.Errorf("init container start failed: %v: %s", err, msg))
  17.         return
  18.     }
  20.     // Successfully started the container; clear the entry in the failure
  21.     glog.V(4).Infof("Completed init container %q for pod %q", container.Name, format.Pod(pod))
  22. }

3.6. start containers

创建正常的container。

  1. // Step 6: start containers in podContainerChanges.ContainersToStart.
  2. for _, idx := range podContainerChanges.ContainersToStart {
  3.     container := &pod.Spec.Containers[idx]
  4.     startContainerResult := kubecontainer.NewSyncResult(kubecontainer.StartContainer, container.Name)
  5.     result.AddSyncResult(startContainerResult)
  7.     isInBackOff, msg, err := m.doBackOff(pod, container, podStatus, backOff)
  8.     if isInBackOff {
  9.         startContainerResult.Fail(err, msg)
  10.         glog.V(4).Infof("Backing Off restarting container %+v in pod %v", container, format.Pod(pod))
  11.         continue
  12.     }
  14.     glog.V(4).Infof("Creating container %+v in pod %v", container, format.Pod(pod))
  15.   // 通过startContainer来运行容器
  16.     if msg, err := m.startContainer(podSandboxID, podSandboxConfig, container, pod, podStatus, pullSecrets, podIP, kubecontainer.ContainerTypeRegular); err != nil {
  17.         startContainerResult.Fail(err, msg)
  18.         // known errors that are logged in other places are logged at higher levels here to avoid
  19.         // repetitive log spam
  20.         switch {
  21.         case err == images.ErrImagePullBackOff:
  22.             glog.V(3).Infof("container start failed: %v: %s", err, msg)
  23.         default:
  24.             utilruntime.HandleError(fmt.Errorf("container start failed: %v: %s", err, msg))
  25.         }
  26.         continue
  27.     }
  28. }

4. startContainer

startContainer启动一个容器并返回是否成功。

主要包括以下几个步骤：

  1. 拉取镜像
  2. 创建容器
  3. 启动容器
  4. 运行post start lifecycle hooks(如果有设置此项)

startContainer完整代码如下：

startContainer部分代码位于pkg/kubelet/kuberuntime/kuberuntime_container.go

  1. // startContainer starts a container and returns a message indicates why it is failed on error.
  2. // It starts the container through the following steps:
  3. // * pull the image
  4. // * create the container
  5. // * start the container
  6. // * run the post start lifecycle hooks (if applicable)
  7. func (m *kubeGenericRuntimeManager) startContainer(podSandboxID string, podSandboxConfig *runtimeapi.PodSandboxConfig, container *v1.Container, pod *v1.Pod, podStatus *kubecontainer.PodStatus, pullSecrets []v1.Secret, podIP string, containerType kubecontainer.ContainerType) (string, error) {
  8.     // Step 1: pull the image.
  9.     imageRef, msg, err := m.imagePuller.EnsureImageExists(pod, container, pullSecrets)
  10.     if err != nil {
  11.         m.recordContainerEvent(pod, container, "", v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", grpc.ErrorDesc(err))
  12.         return msg, err
  13.     }
  15.     // Step 2: create the container.
  16.     ref, err := kubecontainer.GenerateContainerRef(pod, container)
  17.     if err != nil {
  18.         glog.Errorf("Can't make a ref to pod %q, container %v: %v", format.Pod(pod), container.Name, err)
  19.     }
  20.     glog.V(4).Infof("Generating ref for container %s: %#v", container.Name, ref)
  22.     // For a new container, the RestartCount should be 0
  23.     restartCount := 0
  24.     containerStatus := podStatus.FindContainerStatusByName(container.Name)
  25.     if containerStatus != nil {
  26.         restartCount = containerStatus.RestartCount + 1
  27.     }
  29.     containerConfig, cleanupAction, err := m.generateContainerConfig(container, pod, restartCount, podIP, imageRef, containerType)
  30.     if cleanupAction != nil {
  31.         defer cleanupAction()
  32.     }
  33.     if err != nil {
  34.         m.recordContainerEvent(pod, container, "", v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", grpc.ErrorDesc(err))
  35.         return grpc.ErrorDesc(err), ErrCreateContainerConfig
  36.     }
  38.     containerID, err := m.runtimeService.CreateContainer(podSandboxID, containerConfig, podSandboxConfig)
  39.     if err != nil {
  40.         m.recordContainerEvent(pod, container, containerID, v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", grpc.ErrorDesc(err))
  41.         return grpc.ErrorDesc(err), ErrCreateContainer
  42.     }
  43.     err = m.internalLifecycle.PreStartContainer(pod, container, containerID)
  44.     if err != nil {
  45.         m.recordContainerEvent(pod, container, containerID, v1.EventTypeWarning, events.FailedToStartContainer, "Internal PreStartContainer hook failed: %v", grpc.ErrorDesc(err))
  46.         return grpc.ErrorDesc(err), ErrPreStartHook
  47.     }
  48.     m.recordContainerEvent(pod, container, containerID, v1.EventTypeNormal, events.CreatedContainer, "Created container")
  50.     if ref != nil {
  51.         m.containerRefManager.SetRef(kubecontainer.ContainerID{
  52.             Type: m.runtimeName,
  53.             ID:   containerID,
  54.         }, ref)
  55.     }
  57.     // Step 3: start the container.
  58.     err = m.runtimeService.StartContainer(containerID)
  59.     if err != nil {
  60.         m.recordContainerEvent(pod, container, containerID, v1.EventTypeWarning, events.FailedToStartContainer, "Error: %v", grpc.ErrorDesc(err))
  61.         return grpc.ErrorDesc(err), kubecontainer.ErrRunContainer
  62.     }
  63.     m.recordContainerEvent(pod, container, containerID, v1.EventTypeNormal, events.StartedContainer, "Started container")
  65.     // Symlink container logs to the legacy container log location for cluster logging
  66.     // support.
  67.     // TODO(random-liu): Remove this after cluster logging supports CRI container log path.
  68.     containerMeta := containerConfig.GetMetadata()
  69.     sandboxMeta := podSandboxConfig.GetMetadata()
  70.     legacySymlink := legacyLogSymlink(containerID, containerMeta.Name, sandboxMeta.Name,
  71.         sandboxMeta.Namespace)
  72.     containerLog := filepath.Join(podSandboxConfig.LogDirectory, containerConfig.LogPath)
  73.     // only create legacy symlink if containerLog path exists (or the error is not IsNotExist).
  74.     // Because if containerLog path does not exist, only dandling legacySymlink is created.
  75.     // This dangling legacySymlink is later removed by container gc, so it does not make sense
  76.     // to create it in the first place. it happens when journald logging driver is used with docker.
  77.     if _, err := m.osInterface.Stat(containerLog); !os.IsNotExist(err) {
  78.         if err := m.osInterface.Symlink(containerLog, legacySymlink); err != nil {
  79.             glog.Errorf("Failed to create legacy symbolic link %q to container %q log %q: %v",
  80.                 legacySymlink, containerID, containerLog, err)
  81.         }
  82.     }
  84.     // Step 4: execute the post start hook.
  85.     if container.Lifecycle != nil && container.Lifecycle.PostStart != nil {
  86.         kubeContainerID := kubecontainer.ContainerID{
  87.             Type: m.runtimeName,
  88.             ID:   containerID,
  89.         }
  90.         msg, handlerErr := m.runner.Run(kubeContainerID, pod, container, container.Lifecycle.PostStart)
  91.         if handlerErr != nil {
  92.             m.recordContainerEvent(pod, container, kubeContainerID.ID, v1.EventTypeWarning, events.FailedPostStartHook, msg)
  93.             if err := m.killContainer(pod, kubeContainerID, container.Name, "FailedPostStartHook", nil); err != nil {
  94.                 glog.Errorf("Failed to kill container %q(id=%q) in pod %q: %v, %v",
  95.                     container.Name, kubeContainerID.String(), format.Pod(pod), ErrPostStartHook, err)
  96.             }
  97.             return msg, fmt.Errorf("%s: %v", ErrPostStartHook, handlerErr)
  98.         }
  99.     }
  101.     return "", nil
  102. }

以下对startContainer分段分析：

4.1. pull image

通过EnsureImageExists方法拉取拉取指定pod容器的镜像，并返回镜像信息和错误。

  1. // Step 1: pull the image.
  2. imageRef, msg, err := m.imagePuller.EnsureImageExists(pod, container, pullSecrets)
  3. if err != nil {
  4.     m.recordContainerEvent(pod, container, "", v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", grpc.ErrorDesc(err))
  5.     return msg, err
  6. }

4.2. CreateContainer

首先生成container的*v1.ObjectReference对象，该对象包括container的相关信息。

  1. // Step 2: create the container.
  2. ref, err := kubecontainer.GenerateContainerRef(pod, container)
  3. if err != nil {
  4.     glog.Errorf("Can't make a ref to pod %q, container %v: %v", format.Pod(pod), container.Name, err)
  5. }
  6. glog.V(4).Infof("Generating ref for container %s: %#v", container.Name, ref)

统计container的重启次数，新的容器默认重启次数为0。

  1. // For a new container, the RestartCount should be 0
  2. restartCount := 0
  3. containerStatus := podStatus.FindContainerStatusByName(container.Name)
  4. if containerStatus != nil {
  5.     restartCount = containerStatus.RestartCount + 1
  6. }

生成container的配置。

  1. containerConfig, cleanupAction, err := m.generateContainerConfig(container, pod, restartCount, podIP, imageRef, containerType)
  2. if cleanupAction != nil {
  3.     defer cleanupAction()
  4. }
  5. if err != nil {
  6.     m.recordContainerEvent(pod, container, "", v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", grpc.ErrorDesc(err))
  7.     return grpc.ErrorDesc(err), ErrCreateContainerConfig
  8. }

调用runtimeService，执行CreateContainer的操作。

  1. containerID, err := m.runtimeService.CreateContainer(podSandboxID, containerConfig, podSandboxConfig)
  2. if err != nil {
  3.     m.recordContainerEvent(pod, container, containerID, v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", grpc.ErrorDesc(err))
  4.     return grpc.ErrorDesc(err), ErrCreateContainer
  5. }
  6. err = m.internalLifecycle.PreStartContainer(pod, container, containerID)
  7. if err != nil {
  8.     m.recordContainerEvent(pod, container, containerID, v1.EventTypeWarning, events.FailedToStartContainer, "Internal PreStartContainer hook failed: %v", grpc.ErrorDesc(err))
  9.     return grpc.ErrorDesc(err), ErrPreStartHook
  10. }
  11. m.recordContainerEvent(pod, container, containerID, v1.EventTypeNormal, events.CreatedContainer, "Created container")
  13. if ref != nil {
  14.     m.containerRefManager.SetRef(kubecontainer.ContainerID{
  15.         Type: m.runtimeName,
  16.         ID:   containerID,
  17.     }, ref)
  18. }

4.3. StartContainer

执行runtimeService的StartContainer方法，来启动容器。

  1. // Step 3: start the container.
  2. err = m.runtimeService.StartContainer(containerID)
  3. if err != nil {
  4.     m.recordContainerEvent(pod, container, containerID, v1.EventTypeWarning, events.FailedToStartContainer, "Error: %v", grpc.ErrorDesc(err))
  5.     return grpc.ErrorDesc(err), kubecontainer.ErrRunContainer
  6. }
  7. m.recordContainerEvent(pod, container, containerID, v1.EventTypeNormal, events.StartedContainer, "Started container")
  9. // Symlink container logs to the legacy container log location for cluster logging
  10. // support.
  11. // TODO(random-liu): Remove this after cluster logging supports CRI container log path.
  12. containerMeta := containerConfig.GetMetadata()
  13. sandboxMeta := podSandboxConfig.GetMetadata()
  14. legacySymlink := legacyLogSymlink(containerID, containerMeta.Name, sandboxMeta.Name,
  15.     sandboxMeta.Namespace)
  16. containerLog := filepath.Join(podSandboxConfig.LogDirectory, containerConfig.LogPath)
  17. // only create legacy symlink if containerLog path exists (or the error is not IsNotExist).
  18. // Because if containerLog path does not exist, only dandling legacySymlink is created.
  19. // This dangling legacySymlink is later removed by container gc, so it does not make sense
  20. // to create it in the first place. it happens when journald logging driver is used with docker.
  21. if _, err := m.osInterface.Stat(containerLog); !os.IsNotExist(err) {
  22.     if err := m.osInterface.Symlink(containerLog, legacySymlink); err != nil {
  23.         glog.Errorf("Failed to create legacy symbolic link %q to container %q log %q: %v",
  24.             legacySymlink, containerID, containerLog, err)
  25.     }
  26. }

4.4. execute post start hook

如果有指定Lifecycle.PostStart，则执行PostStart操作，PostStart如果执行失败，则容器会根据重启的规则进行重启。

  1. // Step 4: execute the post start hook.
  2. if container.Lifecycle != nil && container.Lifecycle.PostStart != nil {
  3.     kubeContainerID := kubecontainer.ContainerID{
  4.         Type: m.runtimeName,
  5.         ID:   containerID,
  6.     }
  7.     msg, handlerErr := m.runner.Run(kubeContainerID, pod, container, container.Lifecycle.PostStart)
  8.     if handlerErr != nil {
  9.         m.recordContainerEvent(pod, container, kubeContainerID.ID, v1.EventTypeWarning, events.FailedPostStartHook, msg)
  10.         if err := m.killContainer(pod, kubeContainerID, container.Name, "FailedPostStartHook", nil); err != nil {
  11.             glog.Errorf("Failed to kill container %q(id=%q) in pod %q: %v, %v",
  12.                 container.Name, kubeContainerID.String(), format.Pod(pod), ErrPostStartHook, err)
  13.         }
  14.         return msg, fmt.Errorf("%s: %v", ErrPostStartHook, handlerErr)
  15.     }
  16. }

5. 总结

kubelet的工作是管理pod在Node上的生命周期（包括增删改查），kubelet通过各种类型的manager异步工作各自执行各自的任务，其中使用到了多种的channel来控制状态信号变化的传递，例如比较重要的channel有podUpdates <-chan UpdatePodOptions，来传递pod的变化情况。

创建pod的调用逻辑

syncLoopIteration-->kubetypes.ADD-->HandlePodAdditions(u.Pods)-->dispatchWork(pod, kubetypes.SyncPodCreate, mirrorPod, start)-->podWorkers.UpdatePod-->managePodLoop(podUpdates)-->syncPod(o syncPodOptions)-->containerRuntime.SyncPod-->startContainer

参考：