pod创建源码分析

// syncLoop is the main loop for processing changes. It watches for changes from
// three channels (file, apiserver, and http) and creates a union of them. For
// any new change seen, will run a sync against desired state and running state. If
// no changes are seen to the configuration, will synchronize the last known desired
// state every sync-frequency seconds. Never returns.
// syncLoop是处理更改的主循环。它感知来自三个channel(file,apiserver,http)的pod的变化，并且聚合它们。有任何的改变发生，将运行状态同步为期望状态。反之，则在每个同步周期内同步最后已知的期望状态。
func (kl *Kubelet) syncLoop(updates <-chan kubetypes.PodUpdate, handler SyncHandler) {
 klog.InfoS("Starting kubelet main sync loop")

kl.syncLoopMonitor.Store(kl.clock.Now())
  if !kl.syncLoopIteration(updates, handler, syncTicker.C, housekeepingTicker.C, plegCh) {
   break
  }

// Arguments:
// 1.  configCh:       a channel to read config events from
// 2.  handler:        the SyncHandler to dispatch pods to
// 3.  syncCh:         a channel to read periodic sync events from
// 4.  housekeepingCh: a channel to read housekeeping events from
// 5.  plegCh:         a channel to read PLEG updates from
// * configCh: dispatch the pods for the config change to the appropriate
//             handler callback for the event type
// * plegCh: update the runtime cache; sync pod
// * syncCh: sync all pods waiting for sync
// * housekeepingCh: trigger cleanup of pods
// * health manager: sync pods that have failed or in which one or more
//                     containers have failed health checks
func (kl *Kubelet) syncLoopIteration(configCh <-chan kubetypes.PodUpdate, handler SyncHandler,
 syncCh <-chan time.Time, housekeepingCh <-chan time.Time, plegCh <-chan *pleg.PodLifecycleEvent) bool {
 select {
 case u, open := <-configCh:
  // Update from a config source; dispatch it to the right handler
  // callback.
  if !open {
   klog.ErrorS(nil, "Update channel is closed, exiting the sync loop")
   return false
  }

// SyncHandler is an interface implemented by Kubelet, for testability
# pod创建、更新、 删除...
type SyncHandler interface {
 HandlePodAdditions(pods []*v1.Pod) 
 HandlePodUpdates(pods []*v1.Pod) 
 HandlePodRemoves(pods []*v1.Pod)
 HandlePodReconcile(pods []*v1.Pod)
 HandlePodSyncs(pods []*v1.Pod)
 HandlePodCleanups() error
}

// These constants identify the PodOperations that can be made on a pod configuration.
const (
 // SET is the current pod configuration.
 SET PodOperation = iota
 // ADD signifies pods that are new to this source.
 ADD
 // DELETE signifies pods that are gracefully deleted from this source.
 DELETE
 // REMOVE signifies pods that have been removed from this source.
 REMOVE
 // UPDATE signifies pods have been updated in this source.
 UPDATE
 // RECONCILE signifies pods that have unexpected status in this source,
 // kubelet should reconcile status with this source.
 RECONCILE
)
switch u.Op {
  case kubetypes.ADD:
   klog.V(2).InfoS("SyncLoop ADD", "source", u.Source, "pods", format.Pods(u.Pods))
   // After restarting, kubelet will get all existing pods through
   // ADD as if they are new pods. These pods will then go through the
   // admission process and *may* be rejected. This can be resolved
   // once we have checkpointing.
   handler.HandlePodAdditions(u.Pods)

1. 根据pod的创建时间进行排序
sort.Sort(sliceutils.PodsByCreationTime(pods))
2. 将pod添加到podmanager中.因为kubelet它会依赖这个pod manager作为期望状态的一个凭证。
如果一个在pod manager中无法查询，那么就意味着它已经被apiserver删除了，不再需要其他操作
// Always add the pod to the pod manager. Kubelet relies on the pod
// manager as the source of truth for the desired state. If a pod does
// not exist in the pod manager, it means that it has been deleted in
// the apiserver and no action (other than cleanup) is required.
kl.podManager.AddPod(pod)
3. 判断pod是不是静态pod
mirrorPod, _ := kl.podManager.GetMirrorPodByPod(pod)
4. 通过dispatchWork分发任务
kl.dispatchWork(pod, kubetypes.SyncPodCreate, mirrorPod, start)
5. 将pod加入到probe manager，即健康检查.包括startup probe、liveness probe、readiness probe。 
kl.probeManager.AddPod(pod)

// Run the sync in an async worker. 在一个异步worker中执行同步
 kl.podWorkers.UpdatePod(&UpdatePodOptions{
  Pod:        pod,
  MirrorPod:  mirrorPod,
  UpdateType: syncType,
  OnCompleteFunc: func(err error) {
   if err != nil {
    metrics.PodWorkerDuration.WithLabelValues(syncType.String()).Observe(metrics.SinceInSeconds(start))
   }
  },
 })

// Creating a new pod worker either means this is a new pod, or that the
  // kubelet just restarted. In either case the kubelet is willing to believe
  // the status of the pod for the first pod worker sync. See corresponding
  // comment in syncPod.
    // 创建一个新的pod worker，意味着这是一个新的pod
  go func() {
   defer runtime.HandleCrash()
   p.managePodLoop(podUpdates)
  }()

for update := range podUpdates {
  err := func() error {
   podUID := update.Pod.UID
   // This is a blocking call that would return only if the cache
   // has an entry for the pod that is newer than minRuntimeCache
   // Time. This ensures the worker doesn't start syncing until
   // after the cache is at least newer than the finished time of
   // the previous sync.
   status, err := p.podCache.GetNewerThan(podUID, lastSyncTime)
   if err != nil {
    // This is the legacy event thrown by manage pod loop
    // all other events are now dispatched from syncPodFn
    p.recorder.Eventf(update.Pod, v1.EventTypeWarning, events.FailedSync, "error determining status: %v", err)
    return err
   }
      // 这里去做同步
   err = p.syncPodFn(syncPodOptions{
    mirrorPod:      update.MirrorPod,
    pod:            update.Pod,
    podStatus:      status,
    killPodOptions: update.KillPodOptions,
    updateType:     update.UpdateType,
   })
   lastSyncTime = time.Now()
   return err
  }()

// SyncPod syncs the running pod into the desired pod by executing following steps:
// 执行以下的步骤将运行的pod同步到期望的状态
//  1. Compute sandbox and container changes.
// 计算sanbox和container改变
//  2. Kill pod sandbox if necessary.
// 如果有必要就删除pod sandbox
//  3. Kill any containers that should not be running.
// 删除不需要运行的容器
//  4. Create sandbox if necessary.
// 需要的情况下创建sandbox
//  5. Create ephemeral containers.
// 创建临时容器
//  6. Create init containers.
// 创建初始化容器
//  7. Create normal containers.
// 创建普通容器
func (m *kubeGenericRuntimeManager) SyncPod()
// Step 1: Compute sandbox and container changes.
 podContainerChanges := m.computePodActions(pod, podStatus)
 klog.V(3).InfoS("computePodActions got for pod", "podActions", podContainerChanges, "pod", klog.KObj(pod))
 if podContainerChanges.CreateSandbox {
  ref, err := ref.GetReference(legacyscheme.Scheme, pod)
  if err != nil {
   klog.ErrorS(err, "Couldn't make a ref to pod", "pod", klog.KObj(pod))
  }
  if podContainerChanges.SandboxID != "" {
   m.recorder.Eventf(ref, v1.EventTypeNormal, events.SandboxChanged, "Pod sandbox changed, it will be killed and re-created.")
  } else {
   klog.V(4).InfoS("SyncPod received new pod, will create a sandbox for it", "pod", klog.KObj(pod))
  }
 }
  // Step 2: Kill the pod if the sandbox has changed.
 if podContainerChanges.KillPod {
  // Step 3: kill any running containers in this pod which are not to keep.
  for containerID, containerInfo := range podContainerChanges.ContainersToKill {
   klog.V(3).InfoS("Killing unwanted container for pod", "containerName", containerInfo.name, "containerID", containerID, "pod", klog.KObj(pod))
   killContainerResult := kubecontainer.NewSyncResult(kubecontainer.KillContainer, containerInfo.name)
   result.AddSyncResult(killContainerResult)
   if err := m.killContainer(pod, containerID, containerInfo.name, containerInfo.message, containerInfo.reason, nil); err != nil {
    killContainerResult.Fail(kubecontainer.ErrKillContainer, err.Error())
    klog.ErrorS(err, "killContainer for pod failed", "containerName", containerInfo.name, "containerID", containerID, "pod", klog.KObj(pod))
    return
   }
      // Step 4: Create a sandbox for the pod if necessary.
 podSandboxID := podContainerChanges.SandboxID
 if podContainerChanges.CreateSandbox {
  var msg string
  var err error
  klog.V(4).InfoS("Creating PodSandbox for pod", "pod", klog.KObj(pod))
  createSandboxResult := kubecontainer.NewSyncResult(kubecontainer.CreatePodSandbox, format.Pod(pod))
  result.AddSyncResult(createSandboxResult)
  podSandboxID, msg, err = m.createPodSandbox(pod, podContainerChanges.Attempt)
    // Step 5: start ephemeral containers
 // These are started "prior" to init containers to allow running ephemeral containers even when there
 // are errors starting an init container. In practice init containers will start first since ephemeral
 // containers cannot be specified on pod creation.
 if utilfeature.DefaultFeatureGate.Enabled(features.EphemeralContainers) {
  for _, idx := range podContainerChanges.EphemeralContainersToStart {
   start("ephemeral container", ephemeralContainerStartSpec(&pod.Spec.EphemeralContainers[idx]))
  }
 }
  // Step 6: start the init container.
 if container := podContainerChanges.NextInitContainerToStart; container != nil {
  // Start the next init container.
  if err := start("init container", containerStartSpec(container)); err != nil {
   return
  }
  // Successfully started the container; clear the entry in the failure
  klog.V(4).InfoS("Completed init container for pod", "containerName", container.Name, "pod", klog.KObj(pod))
 }
 // Step 7: start containers in podContainerChanges.ContainersToStart.
 for _, idx := range podContainerChanges.ContainersToStart {
  start("container", containerStartSpec(&pod.Spec.Containers[idx]))
 }

# 创建pod数据目录、volume、获取image pull secrets。。。
newPodWorkers(klet.syncPod --->pkg/kubelet/kubelet.go） //通过syncPod
                               kubetypes.SyncPodKill
                                kubetypes.SyncPodCreate
                                podStatus.IPs = append(podStatus.IPs, ipInfo.IP)
                                runnable.Admit
                                kubetypes.IsStaticPod(pod)
                               kl.makePodDataDirs(pod)
                                kl.volumeManager.WaitForAttachAndMount(pod)
                                kl.getPullSecretsForPod(pod)
                                kl.containerRuntime.SyncPod(pkg/kubelet/container