启动容器

启动pod容器流程分为三个步骤:

  1. 启动临时容器
  2. 启动初始化容器
  3. 启动业务容器

以上三种类型的启动流程基本一致,均通过调用startContainer函数实现

启动pod容器的源码实现

func (m *kubeGenericRuntimeManager) SyncPod(pod *v1.Pod, podStatus *kubecontainer.PodStatus, pullSecrets []v1.Secret, backOff *flowcontrol.Backoff) (result kubecontainer.PodSyncResult) {
...
    // Helper containing boilerplate common to starting all types of containers.
    // typeName is a label used to describe this type of container in log messages,
    // currently: "container", "init container" or "ephemeral container"
    start := func(typeName string, spec *startSpec) error {
        startContainerResult := kubecontainer.NewSyncResult(kubecontainer.StartContainer, spec.container.Name)
        result.AddSyncResult(startContainerResult)

        isInBackOff, msg, err := m.doBackOff(pod, spec.container, podStatus, backOff)
        if isInBackOff {
            startContainerResult.Fail(err, msg)
            klog.V(4).Infof("Backing Off restarting %v %+v in pod %v", typeName, spec.container, format.Pod(pod))
            return err
        }

        klog.V(4).Infof("Creating %v %+v in pod %v", typeName, spec.container, format.Pod(pod))
        // NOTE (aramase) podIPs are populated for single stack and dual stack clusters. Send only podIPs.
        if msg, err := m.startContainer(podSandboxID, podSandboxConfig, spec, pod, podStatus, pullSecrets, podIP, podIPs); err != nil {
            startContainerResult.Fail(err, msg)
            // known errors that are logged in other places are logged at higher levels here to avoid
            // repetitive log spam
            switch {
            case err == images.ErrImagePullBackOff:
                klog.V(3).Infof("%v start failed: %v: %s", typeName, err, msg)
            default:
                utilruntime.HandleError(fmt.Errorf("%v start failed: %v: %s", typeName, err, msg))
            }
            return err
        }

        return nil
    }

    // 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).Infof("Completed init container %q for pod %q", container.Name, format.Pod(pod))
    }

    // Step 7: start containers in podContainerChanges.ContainersToStart.
    for _, idx := range podContainerChanges.ContainersToStart {
        start("container", containerStartSpec(&pod.Spec.Containers[idx]))
    }

    return
}

startContainer函数主要逻辑如下:

  1. 拉取镜像
  2. 创建容器
  3. 启动容器
  4. 执行容器的postStart钩子(容器启动完毕后要执行的逻辑)

后续我们将对startContainer函数着重讨论

startContainer函数源码实现

kubernetes\pkg\kubelet\kuberuntime\kuberuntime_container.go

func (m *kubeGenericRuntimeManager) startContainer(podSandboxID string, podSandboxConfig *runtimeapi.PodSandboxConfig, spec *startSpec, pod *v1.Pod, podStatus *kubecontainer.PodStatus, pullSecrets []v1.Secret, podIP string, podIPs []string) (string, error) {
    container := spec.container

    // Step 1: pull the image.
    imageRef, msg, err := m.imagePuller.EnsureImageExists(pod, container, pullSecrets, podSandboxConfig)
    if err != nil {
        s, _ := grpcstatus.FromError(err)
        m.recordContainerEvent(pod, container, "", v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", s.Message())
        return msg, err
    }

    // Step 2: create the container.
    // 生成容器引用,
    ref, err := kubecontainer.GenerateContainerRef(pod, container)
    if err != nil {
        klog.Errorf("Can't make a ref to pod %q, container %v: %v", format.Pod(pod), container.Name, err)
    }
    klog.V(4).Infof("Generating ref for container %s: %#v", container.Name, ref)

    // For a new container, the RestartCount should be 0
    // 如果该容器存在,则重启次数加1
    restartCount := 0
    containerStatus := podStatus.FindContainerStatusByName(container.Name)
    if containerStatus != nil {
        restartCount = containerStatus.RestartCount + 1
    }

    // 生成容器配置-获取临时容器ID
    target, err := spec.getTargetID(podStatus)
    if err != nil {
        s, _ := grpcstatus.FromError(err)
        m.recordContainerEvent(pod, container, "", v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", s.Message())
        return s.Message(), ErrCreateContainerConfig
    }

    // 生成创建容器所需配置:设备列表、volumes列表、环境变量列表、注释列表等
    containerConfig, cleanupAction, err := m.generateContainerConfig(container, pod, restartCount, podIP, imageRef, podIPs, target)
    if cleanupAction != nil {
        defer cleanupAction()
    }
    if err != nil {
        s, _ := grpcstatus.FromError(err)
        m.recordContainerEvent(pod, container, "", v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", s.Message())
        return s.Message(), ErrCreateContainerConfig
    }

    containerID, err := m.runtimeService.CreateContainer(podSandboxID, containerConfig, podSandboxConfig)
    if err != nil {
        s, _ := grpcstatus.FromError(err)
        m.recordContainerEvent(pod, container, containerID, v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", s.Message())
        return s.Message(), ErrCreateContainer
    }
    err = m.internalLifecycle.PreStartContainer(pod, container, containerID)
    if err != nil {
        s, _ := grpcstatus.FromError(err)
        m.recordContainerEvent(pod, container, containerID, v1.EventTypeWarning, events.FailedToStartContainer, "Internal PreStartContainer hook failed: %v", s.Message())
        return s.Message(), ErrPreStartHook
    }
    m.recordContainerEvent(pod, container, containerID, v1.EventTypeNormal, events.CreatedContainer, fmt.Sprintf("Created container %s", container.Name))

    if ref != nil {
        m.containerRefManager.SetRef(kubecontainer.ContainerID{
            Type: m.runtimeName,
            ID:   containerID,
        }, ref)
    }

    // Step 3: start the container.
    err = m.runtimeService.StartContainer(containerID)
    if err != nil {
        s, _ := grpcstatus.FromError(err)
        m.recordContainerEvent(pod, container, containerID, v1.EventTypeWarning, events.FailedToStartContainer, "Error: %v", s.Message())
        return s.Message(), kubecontainer.ErrRunContainer
    }
    m.recordContainerEvent(pod, container, containerID, v1.EventTypeNormal, events.StartedContainer, fmt.Sprintf("Started container %s", container.Name))

    // Symlink container logs to the legacy container log location for cluster logging
    // support.
    // TODO(random-liu): Remove this after cluster logging supports CRI container log path.
    // /var/log/containers
    containerMeta := containerConfig.GetMetadata()
    sandboxMeta := podSandboxConfig.GetMetadata()
    legacySymlink := legacyLogSymlink(containerID, containerMeta.Name, sandboxMeta.Name,
        sandboxMeta.Namespace)
    // podSandboxConfig.LogDirectory="/var/log/pods/default_stakater-reloader-598f958967-ddkl7_2681cb7f-daa4-4620-bb60-1d449709181c"
    //
    containerLog := filepath.Join(podSandboxConfig.LogDirectory, containerConfig.LogPath)
    // only create legacy symlink if containerLog path exists (or the error is not IsNotExist).
    // Because if containerLog path does not exist, only dandling legacySymlink is created.
    // This dangling legacySymlink is later removed by container gc, so it does not make sense
    // to create it in the first place. it happens when journald logging driver is used with docker.
    if _, err := m.osInterface.Stat(containerLog); !os.IsNotExist(err) {
        if err := m.osInterface.Symlink(containerLog, legacySymlink); err != nil {
            klog.Errorf("Failed to create legacy symbolic link %q to container %q log %q: %v",
                legacySymlink, containerID, containerLog, err)
        }
    }

    // Step 4: execute the post start hook.
    if container.Lifecycle != nil && container.Lifecycle.PostStart != nil {
        kubeContainerID := kubecontainer.ContainerID{
            Type: m.runtimeName,
            ID:   containerID,
        }
        msg, handlerErr := m.runner.Run(kubeContainerID, pod, container, container.Lifecycle.PostStart)
        if handlerErr != nil {
            m.recordContainerEvent(pod, container, kubeContainerID.ID, v1.EventTypeWarning, events.FailedPostStartHook, msg)
            if err := m.killContainer(pod, kubeContainerID, container.Name, "FailedPostStartHook", nil); err != nil {
                klog.Errorf("Failed to kill container %q(id=%q) in pod %q: %v, %v",
                    container.Name, kubeContainerID.String(), format.Pod(pod), ErrPostStartHook, err)
            }
            return msg, fmt.Errorf("%s: %v", ErrPostStartHook, handlerErr)
        }
    }

    return "", nil
}
Copyright © weiliang 2021 all right reserved,powered by Gitbook本书发布时间: 2024-04-22 16:03:41

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