CRI基本原理

      早期的 kubernetes 使用 docker 作为默认的 runtime，后来又加入 rkt，每加入一种新运行时，k8s 都要修改接口。container runtime 加入，不同的容器的实现和功能差异很大。标准就是 CRI（Container RunTime Interface）。k8s 不再关心底层的容器运行时，kubelet只感知到 CRI server，而 CRI server 只需遵循 CRI 标准实现

    CRI 接口定义在 k8s.io/cri-api/pkg/apis/services.go，看看具体定义了哪些接口

RuntimeService 接口

    RuntimeVersioner，负责返回 runtime 名字，版本以及 API 版本，一个接口函数 Version

• Version(apiVersion string) (*runtimeapi.VersionResponse, error)

    ContainerManager，对 container 的操作接口，简单明了

• CreateContainer(podSandboxID string, config *runtimeapi.ContainerConfig, sandboxConfig *runtimeapi.PodSandboxConfig) (string, error)
• StartContainer(containerID string) error
• StopContainer(containerID string, timeout int64) error
• RemoveContainer(containerID string) error
• ListContainers(filter *runtimeapi.ContainerFilter) ([]*runtimeapi.Container, error)
• ContainerStatus(containerID string) (*runtimeapi.ContainerStatus, error)
• UpdateContainerResources(containerID string, resources *runtimeapi.LinuxContainerResources) error
• ExecSync(containerID string, cmd []string, timeout time.Duration) (stdout []byte, stderr []byte, err error)
• Exec(*runtimeapi.ExecRequest) (*runtimeapi.ExecResponse, error)
• Attach(req *runtimeapi.AttachRequest) (*runtimeapi.AttachResponse, error)
• ReopenContainerLog(ContainerID string) error

    PodSandboxManager，负责操作 sandbox （Pause 容器或者虚拟机），是线程安全的，包括方法如下：

• RunPodSandbox(config *runtimeapi.PodSandboxConfig, runtimeHandler string) (string, error)
• StopPodSandbox(podSandboxID string) error
• RemovePodSandbox(podSandboxID string) error
• PodSandboxStatus(podSandboxID string) (*runtimeapi.PodSandboxStatus, error)
• ListPodSandbox(filter *runtimeapi.PodSandboxFilter) ([]*runtimeapi.PodSandbox, error)
• PortForward(*runtimeapi.PortForwardRequest) (*runtimeapi.PortForwardResponse, error)

      状态查询接口等

// RuntimeService interface should be implemented by a container runtime.
// The methods should be thread-safe.
type RuntimeService interface {
   RuntimeVersioner
   ContainerManager
   PodSandboxManager
   ContainerStatsManager

   // UpdateRuntimeConfig updates runtime configuration if specified
   UpdateRuntimeConfig(runtimeConfig *runtimeapi.RuntimeConfig) error
   // Status returns the status of the runtime.
   Status() (*runtimeapi.RuntimeStatus, error)
}

ImageManagerService 接口

    定义了镜像的接口，包括查询，下载，删除等操作

// ImageManagerService interface should be implemented by a container image
// manager.
// The methods should be thread-safe.
type ImageManagerService interface {
	// ListImages lists the existing images.
	ListImages(filter *runtimeapi.ImageFilter) ([]*runtimeapi.Image, error)
	// ImageStatus returns the status of the image.
	ImageStatus(image *runtimeapi.ImageSpec) (*runtimeapi.Image, error)
	// PullImage pulls an image with the authentication config.
	PullImage(image *runtimeapi.ImageSpec, auth *runtimeapi.AuthConfig, podSandboxConfig *runtimeapi.PodSandboxConfig) (string, error)
	// RemoveImage removes the image.
	RemoveImage(image *runtimeapi.ImageSpec) error
	// ImageFsInfo returns information of the filesystem that is used to store images.
	ImageFsInfo() ([]*runtimeapi.FilesystemUsage, error)
}

RunKubelet

        -->  createAndInitKubelet

                 -->  NewMainKubelet

                         -->  getRuntimeAndImageServices （第 1 章节讲解）

                         -->  NewKubeGenericRuntimeManager

1. getRuntimeAndImageServices 函数

    NewRemoteRuntimeService 实例化 remote runtime 服务，实现了上述的 RuntimeService 接口

    NewRemoteImageService 实例化 remote 镜像服务，实现了上述的 ImageManagerService 接口

func getRuntimeAndImageServices(remoteRuntimeEndpoint string, remoteImageEndpoint string, runtimeRequestTimeout metav1.Duration) (internalapi.RuntimeService, internalapi.ImageManagerService, error) {
	rs, err := remote.NewRemoteRuntimeService(remoteRuntimeEndpoint, runtimeRequestTimeout.Duration)
	if err != nil {
		return nil, nil, err
	}
	is, err := remote.NewRemoteImageService(remoteImageEndpoint, runtimeRequestTimeout.Duration)
	if err != nil {
		return nil, nil, err
	}
	return rs, is, err
}

    1.1 NewRemoteRuntimeService 函数

      实现是与 remote endpoint 建立 GRPC 连接，实例化 RemoteRuntimeService，实现了 RuntimeService 接口，实现路径在

pkg/kubelet/remote/remote_runtime.go 中，接口的实现是调用 GRPC 客户端发送 GRPC 请求

// NewRemoteRuntimeService creates a new internalapi.RuntimeService.
func NewRemoteRuntimeService(endpoint string, connectionTimeout time.Duration) (internalapi.RuntimeService, error) {
	klog.V(3).Infof("Connecting to runtime service %s", endpoint)
	addr, dailer, err := util.GetAddressAndDialer(endpoint)
	if err != nil {
		return nil, err
	}
	ctx, cancel := context.WithTimeout(context.Background(), connectionTimeout)
	defer cancel()

	conn, err := grpc.DialContext(ctx, addr, grpc.WithInsecure(), grpc.WithDialer(dailer), grpc.WithDefaultCallOptions(grpc.MaxCallRecvMsgSize(maxMsgSize)))
	if err != nil {
		klog.Errorf("Connect remote runtime %s failed: %v", addr, err)
		return nil, err
	}

	return &RemoteRuntimeService{
		timeout:       connectionTimeout,
		runtimeClient: runtimeapi.NewRuntimeServiceClient(conn),
		logReduction:  logreduction.NewLogReduction(identicalErrorDelay),
	}, nil
}

     1.1.1 RunPodSandbox 创建 sandbox

      向 remote server 发送 GRPC RunPodSandboxRequest 请求

// RunPodSandbox creates and starts a pod-level sandbox. Runtimes should ensure
// the sandbox is in ready state.
func (r *RemoteRuntimeService) RunPodSandbox(config *runtimeapi.PodSandboxConfig, runtimeHandler string) (string, error) {
	// Use 2 times longer timeout for sandbox operation (4 mins by default)
	// TODO: Make the pod sandbox timeout configurable.
	ctx, cancel := getContextWithTimeout(r.timeout * 2)
	defer cancel()

	resp, err := r.runtimeClient.RunPodSandbox(ctx, &runtimeapi.RunPodSandboxRequest{
		Config:         config,
		RuntimeHandler: runtimeHandler,
	})
	if err != nil {
		klog.Errorf("RunPodSandbox from runtime service failed: %v", err)
		return "", err
	}

	if resp.PodSandboxId == "" {
		errorMessage := fmt.Sprintf("PodSandboxId is not set for sandbox %q", config.GetMetadata())
		klog.Errorf("RunPodSandbox failed: %s", errorMessage)
		return "", errors.New(errorMessage)
	}

	return resp.PodSandboxId, nil
}

     1.2 NewRemoteImageService 函数

      实现方式是与 remote 建立 GRPC 连接，实例化 RemoteImageService，实现了上述的 ImageManagerService 接口

，实现路径在 pkg/kubelet/remote/remote_image.go 中，接口的实现是调用 GRPC 客户端发送 GRPC 请求

// NewRemoteImageService creates a new internalapi.ImageManagerService.
func NewRemoteImageService(endpoint string, connectionTimeout time.Duration) (internalapi.ImageManagerService, error) {
	klog.V(3).Infof("Connecting to image service %s", endpoint)
	addr, dailer, err := util.GetAddressAndDialer(endpoint)
	if err != nil {
		return nil, err
	}

	ctx, cancel := context.WithTimeout(context.Background(), connectionTimeout)
	defer cancel()

	conn, err := grpc.DialContext(ctx, addr, grpc.WithInsecure(), grpc.WithDialer(dailer), grpc.WithDefaultCallOptions(grpc.MaxCallRecvMsgSize(maxMsgSize)))
	if err != nil {
		klog.Errorf("Connect remote image service %s failed: %v", addr, err)
		return nil, err
	}

	return &RemoteImageService{
		timeout:     connectionTimeout,
		imageClient: runtimeapi.NewImageServiceClient(conn),
	}, nil
}

2. NewKubeGenericRuntimeManager 函数

    实例化 kubeGenericRuntimeManager，实现了 KubeGenericRuntime 接口，定义在 pkg/kubelet/kuberuntime/kuberuntime_manager.go 中，接口包括，容器运行时，以及命令接口

// NewKubeGenericRuntimeManager creates a new kubeGenericRuntimeManager
func NewKubeGenericRuntimeManager(
	recorder record.EventRecorder,
	livenessManager proberesults.Manager,
	seccompProfileRoot string,
	containerRefManager *kubecontainer.RefManager,
	machineInfo *cadvisorapi.MachineInfo,
	podStateProvider podStateProvider,
	osInterface kubecontainer.OSInterface,
	runtimeHelper kubecontainer.RuntimeHelper,
	httpClient types.HttpGetter,
	imageBackOff *flowcontrol.Backoff,
	serializeImagePulls bool,
	imagePullQPS float32,
	imagePullBurst int,
	cpuCFSQuota bool,
	cpuCFSQuotaPeriod metav1.Duration,
	runtimeService internalapi.RuntimeService,
	imageService internalapi.ImageManagerService,
	internalLifecycle cm.InternalContainerLifecycle,
	legacyLogProvider LegacyLogProvider,
	runtimeClassManager *runtimeclass.Manager,
) (KubeGenericRuntime, error)

    赋值 runtime

klet.containerRuntime = runtime
klet.streamingRuntime = runtime
klet.runner = runtime

最后

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