kubernetes/k8s CRI分析-kubelet删除pod分析

2021-08-15

关联博客《kubernetes/k8s CRI 分析-容器运行时接口分析》
《kubernetes/k8s CRI分析-kubelet创建pod分析》

之前的博文先对 CRI 做了介绍,然后对 kubelet CRI 相关源码包括 kubelet 组件 CRI 相关启动参数分析、CRI 相关 interface/struct 分析、CRI 相关初始化分析、kubelet调用CRI创建pod分析 4 个部分进行了分析,没有看的小伙伴,可以点击上面的链接去看一下。

把之前博客分析到的 CRI 架构图再贴出来一遍。

本篇博文将对 kubelet 调用 CRI 删除 pod 做分析。

kubelet中CRI相关的源码分析

kubelet的CRI源码分析包括如下几部分:
(1)kubelet CRI相关启动参数分析;
(2)kubelet CRI相关interface/struct分析;
(3)kubelet CRI初始化分析;
(4)kubelet调用CRI创建pod分析;
(5)kubelet调用CRI删除pod分析。

上两篇博文先对前四部分做了分析,本篇博文将对kubelet调用CRI删除pod做分析。

基于tag v1.17.4

https://github.com/kubernetes/kubernetes/releases/tag/v1.17.4

5.kubelet调用CRI删除pod分析

kubelet CRI删除pod调用流程

下面以kubelet dockershim删除pod调用流程为例做一下分析。

kubelet通过调用dockershim来停止容器,而dockershim则调用docker来停止容器,并调用CNI来删除pod网络。

图1:kubelet dockershim删除pod调用图示

dockershim属于kubelet内置CRI shim,其余remote CRI shim的创建pod调用流程其实与dockershim调用基本一致,只不过是调用了不同的容器引擎来操作容器,但一样由CRI shim调用CNI来删除pod网络。

下面进行详细的源码分析。

直接看到kubeGenericRuntimeManagerKillPod方法,调用CRI删除pod的逻辑将在该方法里触发发起。

从该方法代码也可以看出,kubelet删除一个pod的逻辑为:
(1)先停止属于该pod的所有containers;
(2)然后再停止pod sandbox容器。

注意点:这里只是停止容器,而删除容器的操作由kubelet的gc来做。

// pkg/kubelet/kuberuntime/kuberuntime_manager.go
// KillPod kills all the containers of a pod. Pod may be nil, running pod must not be.
// gracePeriodOverride if specified allows the caller to override the pod default grace period.
// only hard kill paths are allowed to specify a gracePeriodOverride in the kubelet in order to not corrupt user data.
// it is useful when doing SIGKILL for hard eviction scenarios, or max grace period during soft eviction scenarios.
func (m *kubeGenericRuntimeManager) KillPod(pod *v1.Pod, runningPod kubecontainer.Pod, gracePeriodOverride *int64) error {
	err := m.killPodWithSyncResult(pod, runningPod, gracePeriodOverride)
	return err.Error()
}

// killPodWithSyncResult kills a runningPod and returns SyncResult.
// Note: The pod passed in could be *nil* when kubelet restarted.
func (m *kubeGenericRuntimeManager) killPodWithSyncResult(pod *v1.Pod, runningPod kubecontainer.Pod, gracePeriodOverride *int64) (result kubecontainer.PodSyncResult) {
	killContainerResults := m.killContainersWithSyncResult(pod, runningPod, gracePeriodOverride)
	for _, containerResult := range killContainerResults {
		result.AddSyncResult(containerResult)
	}

	// stop sandbox, the sandbox will be removed in GarbageCollect
	killSandboxResult := kubecontainer.NewSyncResult(kubecontainer.KillPodSandbox, runningPod.ID)
	result.AddSyncResult(killSandboxResult)
	// Stop all sandboxes belongs to same pod
	for _, podSandbox := range runningPod.Sandboxes {
		if err := m.runtimeService.StopPodSandbox(podSandbox.ID.ID); err != nil {
			killSandboxResult.Fail(kubecontainer.ErrKillPodSandbox, err.Error())
			klog.Errorf("Failed to stop sandbox %q", podSandbox.ID)
		}
	}

	return
}
5.1 m.killContainersWithSyncResult

m.killContainersWithSyncResult作用:停止属于该pod的所有containers。

主要逻辑:起与容器数量相同的goroutine,调用m.killContainer来停止容器。

// pkg/kubelet/kuberuntime/kuberuntime_container.go
// killContainersWithSyncResult kills all pod's containers with sync results.
func (m *kubeGenericRuntimeManager) killContainersWithSyncResult(pod *v1.Pod, runningPod kubecontainer.Pod, gracePeriodOverride *int64) (syncResults []*kubecontainer.SyncResult) {
	containerResults := make(chan *kubecontainer.SyncResult, len(runningPod.Containers))
	wg := sync.WaitGroup{}

	wg.Add(len(runningPod.Containers))
	for _, container := range runningPod.Containers {
		go func(container *kubecontainer.Container) {
			defer utilruntime.HandleCrash()
			defer wg.Done()

			killContainerResult := kubecontainer.NewSyncResult(kubecontainer.KillContainer, container.Name)
			if err := m.killContainer(pod, container.ID, container.Name, "", gracePeriodOverride); err != nil {
				killContainerResult.Fail(kubecontainer.ErrKillContainer, err.Error())
			}
			containerResults <- killContainerResult
		}(container)
	}
	wg.Wait()
	close(containerResults)

	for containerResult := range containerResults {
		syncResults = append(syncResults, containerResult)
	}
	return
}
5.1.1 m.killContainer

m.killContainer方法主要是调用m.runtimeService.StopContainer

runtimeService即RemoteRuntimeService,实现了CRI shim客户端-容器运行时接口RuntimeService interface,持有与CRI shim容器运行时服务端通信的客户端。所以调用m.runtimeService.StopContainer,实际上等于调用了CRI shim服务端的StopContainer方法,来进行容器的停止操作。

// pkg/kubelet/kuberuntime/kuberuntime_container.go
// killContainer kills a container through the following steps:
// * Run the pre-stop lifecycle hooks (if applicable).
// * Stop the container.
func (m *kubeGenericRuntimeManager) killContainer(pod *v1.Pod, containerID kubecontainer.ContainerID, containerName string, message string, gracePeriodOverride *int64) error {
	...

	klog.V(2).Infof("Killing container %q with %d second grace period", containerID.String(), gracePeriod)

	err := m.runtimeService.StopContainer(containerID.ID, gracePeriod)
	if err != nil {
		klog.Errorf("Container %q termination failed with gracePeriod %d: %v", containerID.String(), gracePeriod, err)
	} else {
		klog.V(3).Infof("Container %q exited normally", containerID.String())
	}

	m.containerRefManager.ClearRef(containerID)

	return err
}
m.runtimeService.StopContainer

m.runtimeService.StopContainer方法,会调用r.runtimeClient.StopContainer,即利用CRI shim客户端,调用CRI shim服务端来进行停止容器的操作。

分析到这里,kubelet中的CRI相关调用就分析完毕了,接下来将会进入到CRI shim(以kubelet内置CRI shim-dockershim为例)里进行停止容器的操作分析。

// pkg/kubelet/remote/remote_runtime.go
// StopContainer stops a running container with a grace period (i.e., timeout).
func (r *RemoteRuntimeService) StopContainer(containerID string, timeout int64) error {
	// Use timeout + default timeout (2 minutes) as timeout to leave extra time
	// for SIGKILL container and request latency.
	t := r.timeout + time.Duration(timeout)*time.Second
	ctx, cancel := getContextWithTimeout(t)
	defer cancel()

	r.logReduction.ClearID(containerID)
	_, err := r.runtimeClient.StopContainer(ctx, &runtimeapi.StopContainerRequest{
		ContainerId: containerID,
		Timeout:     timeout,
	})
	if err != nil {
		klog.Errorf("StopContainer %q from runtime service failed: %v", containerID, err)
		return err
	}

	return nil
}
5.1.2 r.runtimeClient.StopContainer

接下来将会以dockershim为例,进入到CRI shim来进行停止容器操作的分析。

前面kubelet调用r.runtimeClient.StopContainer,会进入到dockershim下面的StopContainer方法。

// pkg/kubelet/dockershim/docker_container.go
// StopContainer stops a running container with a grace period (i.e., timeout).
func (ds *dockerService) StopContainer(_ context.Context, r *runtimeapi.StopContainerRequest) (*runtimeapi.StopContainerResponse, error) {
	err := ds.client.StopContainer(r.ContainerId, time.Duration(r.Timeout)*time.Second)
	if err != nil {
		return nil, err
	}
	return &runtimeapi.StopContainerResponse{}, nil
}
ds.client.StopContainer

主要是调用d.client.ContainerStop

// pkg/kubelet/dockershim/libdocker/kube_docker_client.go
// Stopping an already stopped container will not cause an error in dockerapi.
func (d *kubeDockerClient) StopContainer(id string, timeout time.Duration) error {
	ctx, cancel := d.getCustomTimeoutContext(timeout)
	defer cancel()
	err := d.client.ContainerStop(ctx, id, &timeout)
	if ctxErr := contextError(ctx); ctxErr != nil {
		return ctxErr
	}
	return err
}
d.client.ContainerStop

构建请求参数,向docker指定的url发送http请求,停止容器。

// vendor/github.com/docker/docker/client/container_stop.go
// ContainerStop stops a container. In case the container fails to stop
// gracefully within a time frame specified by the timeout argument,
// it is forcefully terminated (killed).
//
// If the timeout is nil, the container's StopTimeout value is used, if set,
// otherwise the engine default. A negative timeout value can be specified,
// meaning no timeout, i.e. no forceful termination is performed.
func (cli *Client) ContainerStop(ctx context.Context, containerID string, timeout *time.Duration) error {
	query := url.Values{}
	if timeout != nil {
		query.Set("t", timetypes.DurationToSecondsString(*timeout))
	}
	resp, err := cli.post(ctx, "/containers/"+containerID+"/stop", query, nil, nil)
	ensureReaderClosed(resp)
	return err
}
5.2 m.runtimeService.StopPodSandbox

m.runtimeService.StopPodSandbox中的runtimeService即RemoteRuntimeService,其实现了CRI shim客户端-容器运行时接口RuntimeService interface,持有与CRI shim容器运行时服务端通信的客户端。所以调用m.runtimeService.StopPodSandbox,实际上等于调用了CRI shim服务端的StopPodSandbox方法,来进行pod sandbox的停止操作。

分析到这里,kubelet中的CRI相关调用就分析完毕了,接下来将会进入到CRI shim(以kubelet内置CRI shim-dockershim为例)里进行停止pod sandbox的分析。

// pkg/kubelet/remote/remote_runtime.go
// StopPodSandbox stops the sandbox. If there are any running containers in the
// sandbox, they should be forced to termination.
func (r *RemoteRuntimeService) StopPodSandbox(podSandBoxID string) error {
	ctx, cancel := getContextWithTimeout(r.timeout)
	defer cancel()

	_, err := r.runtimeClient.StopPodSandbox(ctx, &runtimeapi.StopPodSandboxRequest{
		PodSandboxId: podSandBoxID,
	})
	if err != nil {
		klog.Errorf("StopPodSandbox %q from runtime service failed: %v", podSandBoxID, err)
		return err
	}

	return nil
}
5.2.1 r.runtimeClient.StopPodSandbox

接下来将会以dockershim为例,进入到CRI shim来进行停止pod sandbox的分析。

前面kubelet调用r.runtimeClient.StopPodSandbox,会进入到dockershim下面的StopPodSandbox方法。

停止pod sandbox主要有2个步骤:
(1)调用ds.network.TearDownPod:删除pod网络;
(2)调用ds.client.StopContainer:停止pod sandbox容器。

需要注意的是,上面的2个步骤只有都成功了,停止pod sandbox的操作才算成功,且上面2个步骤成功的先后顺序没有要求。

// pkg/kubelet/dockershim/docker_sandbox.go
// StopPodSandbox stops the sandbox. If there are any running containers in the
// sandbox, they should be force terminated.
// TODO: This function blocks sandbox teardown on networking teardown. Is it
// better to cut our losses assuming an out of band GC routine will cleanup
// after us?
func (ds *dockerService) StopPodSandbox(ctx context.Context, r *runtimeapi.StopPodSandboxRequest) (*runtimeapi.StopPodSandboxResponse, error) {
	var namespace, name string
	var hostNetwork bool

	podSandboxID := r.PodSandboxId
	resp := &runtimeapi.StopPodSandboxResponse{}

	// Try to retrieve minimal sandbox information from docker daemon or sandbox checkpoint.
	inspectResult, metadata, statusErr := ds.getPodSandboxDetails(podSandboxID)
	if statusErr == nil {
		namespace = metadata.Namespace
		name = metadata.Name
		hostNetwork = (networkNamespaceMode(inspectResult) == runtimeapi.NamespaceMode_NODE)
	} else {
		checkpoint := NewPodSandboxCheckpoint("", "", &CheckpointData{})
		checkpointErr := ds.checkpointManager.GetCheckpoint(podSandboxID, checkpoint)

		// Proceed if both sandbox container and checkpoint could not be found. This means that following
		// actions will only have sandbox ID and not have pod namespace and name information.
		// Return error if encounter any unexpected error.
		if checkpointErr != nil {
			if checkpointErr != errors.ErrCheckpointNotFound {
				err := ds.checkpointManager.RemoveCheckpoint(podSandboxID)
				if err != nil {
					klog.Errorf("Failed to delete corrupt checkpoint for sandbox %q: %v", podSandboxID, err)
				}
			}
			if libdocker.IsContainerNotFoundError(statusErr) {
				klog.Warningf("Both sandbox container and checkpoint for id %q could not be found. "+
					"Proceed without further sandbox information.", podSandboxID)
			} else {
				return nil, utilerrors.NewAggregate([]error{
					fmt.Errorf("failed to get checkpoint for sandbox %q: %v", podSandboxID, checkpointErr),
					fmt.Errorf("failed to get sandbox status: %v", statusErr)})
			}
		} else {
			_, name, namespace, _, hostNetwork = checkpoint.GetData()
		}
	}

	// WARNING: The following operations made the following assumption:
	// 1. kubelet will retry on any error returned by StopPodSandbox.
	// 2. tearing down network and stopping sandbox container can succeed in any sequence.
	// This depends on the implementation detail of network plugin and proper error handling.
	// For kubenet, if tearing down network failed and sandbox container is stopped, kubelet
	// will retry. On retry, kubenet will not be able to retrieve network namespace of the sandbox
	// since it is stopped. With empty network namespcae, CNI bridge plugin will conduct best
	// effort clean up and will not return error.
	errList := []error{}
	ready, ok := ds.getNetworkReady(podSandboxID)
	if !hostNetwork && (ready || !ok) {
		// Only tear down the pod network if we haven't done so already
		cID := kubecontainer.BuildContainerID(runtimeName, podSandboxID)
		err := ds.network.TearDownPod(namespace, name, cID)
		if err == nil {
			ds.setNetworkReady(podSandboxID, false)
		} else {
			errList = append(errList, err)
		}
	}
	if err := ds.client.StopContainer(podSandboxID, defaultSandboxGracePeriod); err != nil {
		// Do not return error if the container does not exist
		if !libdocker.IsContainerNotFoundError(err) {
			klog.Errorf("Failed to stop sandbox %q: %v", podSandboxID, err)
			errList = append(errList, err)
		} else {
			// remove the checkpoint for any sandbox that is not found in the runtime
			ds.checkpointManager.RemoveCheckpoint(podSandboxID)
		}
	}

	if len(errList) == 0 {
		return resp, nil
	}

	// TODO: Stop all running containers in the sandbox.
	return nil, utilerrors.NewAggregate(errList)
}
ds.client.StopContainer

主要是调用d.client.ContainerStop

// pkg/kubelet/dockershim/libdocker/kube_docker_client.go
// Stopping an already stopped container will not cause an error in dockerapi.
func (d *kubeDockerClient) StopContainer(id string, timeout time.Duration) error {
	ctx, cancel := d.getCustomTimeoutContext(timeout)
	defer cancel()
	err := d.client.ContainerStop(ctx, id, &timeout)
	if ctxErr := contextError(ctx); ctxErr != nil {
		return ctxErr
	}
	return err
}
d.client.ContainerStop

构建请求参数,向docker指定的url发送http请求,停止pod sandbox容器。

// vendor/github.com/docker/docker/client/container_stop.go
// ContainerStop stops a container. In case the container fails to stop
// gracefully within a time frame specified by the timeout argument,
// it is forcefully terminated (killed).
//
// If the timeout is nil, the container's StopTimeout value is used, if set,
// otherwise the engine default. A negative timeout value can be specified,
// meaning no timeout, i.e. no forceful termination is performed.
func (cli *Client) ContainerStop(ctx context.Context, containerID string, timeout *time.Duration) error {
	query := url.Values{}
	if timeout != nil {
		query.Set("t", timetypes.DurationToSecondsString(*timeout))
	}
	resp, err := cli.post(ctx, "/containers/"+containerID+"/stop", query, nil, nil)
	ensureReaderClosed(resp)
	return err
}

总结

CRI架构图

在 CRI 之下,包括两种类型的容器运行时的实现:
(1)kubelet内置的 dockershim,实现了 Docker 容器引擎的支持以及 CNI 网络插件(包括 kubenet)的支持。dockershim代码内置于kubelet,被kubelet调用,让dockershim起独立的server来建立CRI shim,向kubelet暴露grpc server;
(2)外部的容器运行时,用来支持 rktcontainerd 等容器引擎的外部容器运行时。

kubelet调用CRI删除pod流程分析

kubelet删除一个pod的逻辑为:
(1)先停止属于该pod的所有containers;
(2)然后再停止pod sandbox容器(包括删除pod网络)。

注意点:这里只是停止容器,而删除容器的操作由kubelet的gc来做。

kubelet CRI删除pod调用流程

下面以kubelet dockershim删除pod调用流程为例做一下分析。

kubelet通过调用dockershim来停止容器,而dockershim则调用docker来停止容器,并调用CNI来删除pod网络。

图1:kubelet dockershim删除pod调用图示

dockershim属于kubelet内置CRI shim,其余remote CRI shim的创建pod调用流程其实与dockershim调用基本一致,只不过是调用了不同的容器引擎来操作容器,但一样由CRI shim调用CNI来删除pod网络。

关联博客《kubernetes/k8s CRI 分析-容器运行时接口分析》
《kubernetes/k8s CRI分析-kubelet创建pod分析》