Container Runtime Interface(CRI)

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CRI为k8s提供的kubelet扩展接口，用来支持多种容器运行时。CRI协议为protobuf格式，kubelet作为客户端，容器运行时作为服务端，两者通过gRpc协议通讯。下面主要解读 CRI的协议定义

spec解读

RuntimeService

https://github.com/kata-containers/kata-containers/blob/main/docs/design/arch-images/api-to-construct.png

包括了Pod和容器相关的操作。

Pod相关的操作包括：

  1. 启：RunPodSandbox
  2. 停：StopPodSandbox
  3. 删：RemovePodSandbox
  4. 查：PodSandboxStatus、ListPodSandbox、ListPodSandboxStats、PodSandboxStats

容器相关的操作：

  1. 增、启：CreateContainer、StartContainer
  2. 停：StopContainer
  3. 删：RemoveContainer
  4. 查：ListContainers、ContainerStatus、
  5. 改：UpdateContainerResources
  6. 控：ReopenContainerLog、ExecSync、Exec、Attach、PortForward
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// Runtime service defines the public APIs for remote container runtimes
service RuntimeService {
    // Version returns the runtime name, runtime version, and runtime API version.
    rpc Version(VersionRequest) returns (VersionResponse) {}

    // RunPodSandbox creates and starts a pod-level sandbox. Runtimes must ensure
    // the sandbox is in the ready state on success.
    rpc RunPodSandbox(RunPodSandboxRequest) returns (RunPodSandboxResponse) {}

    // StopPodSandbox stops any running process that is part of the sandbox and
    // reclaims network resources (e.g., IP addresses) allocated to the sandbox.
    // If there are any running containers in the sandbox, they must be forcibly
    // terminated.
    // This call is idempotent, and must not return an error if all relevant
    // resources have already been reclaimed. kubelet will call StopPodSandbox
    // at least once before calling RemovePodSandbox. It will also attempt to
    // reclaim resources eagerly, as soon as a sandbox is not needed. Hence,
    // multiple StopPodSandbox calls are expected.

    rpc StopPodSandbox(StopPodSandboxRequest) returns (StopPodSandboxResponse) {}
    // RemovePodSandbox removes the sandbox. If there are any running containers
    // in the sandbox, they must be forcibly terminated and removed.
    // This call is idempotent, and must not return an error if the sandbox has
    // already been removed.

    rpc RemovePodSandbox(RemovePodSandboxRequest) returns (RemovePodSandboxResponse) {}
    // PodSandboxStatus returns the status of the PodSandbox. If the PodSandbox is not
    // present, returns an error.

    rpc PodSandboxStatus(PodSandboxStatusRequest) returns (PodSandboxStatusResponse) {}

    // ListPodSandbox returns a list of PodSandboxes.
    rpc ListPodSandbox(ListPodSandboxRequest) returns (ListPodSandboxResponse) {}

    // CreateContainer creates a new container in specified PodSandbox
    rpc CreateContainer(CreateContainerRequest) returns (CreateContainerResponse) {}

    // StartContainer starts the container.
    rpc StartContainer(StartContainerRequest) returns (StartContainerResponse) {}

    // StopContainer stops a running container with a grace period (i.e., timeout).
    // This call is idempotent, and must not return an error if the container has
    // already been stopped.
    // The runtime must forcibly kill the container after the grace period is
    // reached.
    rpc StopContainer(StopContainerRequest) returns (StopContainerResponse) {}

    // RemoveContainer removes the container. If the container is running, the
    // container must be forcibly removed.
    // This call is idempotent, and must not return an error if the container has
    // already been removed.

    rpc RemoveContainer(RemoveContainerRequest) returns (RemoveContainerResponse) {}

    // ListContainers lists all containers by filters.
    rpc ListContainers(ListContainersRequest) returns (ListContainersResponse) {}

    // ContainerStatus returns status of the container. If the container is not
    // present, returns an error.
    rpc ContainerStatus(ContainerStatusRequest) returns (ContainerStatusResponse) {}

    // UpdateContainerResources updates ContainerConfig of the container.
    rpc UpdateContainerResources(UpdateContainerResourcesRequest) returns (UpdateContainerResourcesResponse) {}

    // ReopenContainerLog asks runtime to reopen the stdout/stderr log file
    // for the container. This is often called after the log file has been
    // rotated. If the container is not running, container runtime can choose
    // to either create a new log file and return nil, or return an error.
    // Once it returns error, new container log file MUST NOT be created.
    rpc ReopenContainerLog(ReopenContainerLogRequest) returns (ReopenContainerLogResponse) {}

    // ExecSync runs a command in a container synchronously.
    rpc ExecSync(ExecSyncRequest) returns (ExecSyncResponse) {}

    // Exec prepares a streaming endpoint to execute a command in the container.
    rpc Exec(ExecRequest) returns (ExecResponse) {}

    // Attach prepares a streaming endpoint to attach to a running container.
    rpc Attach(AttachRequest) returns (AttachResponse) {}

    // PortForward prepares a streaming endpoint to forward ports from a PodSandbox.
    rpc PortForward(PortForwardRequest) returns (PortForwardResponse) {}

    // ContainerStats returns stats of the container. If the container does not
    // exist, the call returns an error.
    rpc ContainerStats(ContainerStatsRequest) returns (ContainerStatsResponse) {}

    // ListContainerStats returns stats of all running containers.
    rpc ListContainerStats(ListContainerStatsRequest) returns (ListContainerStatsResponse) {}

    // PodSandboxStats returns stats of the pod sandbox. If the pod sandbox does not
    // exist, the call returns an error.
    rpc PodSandboxStats(PodSandboxStatsRequest) returns (PodSandboxStatsResponse) {}

    // ListPodSandboxStats returns stats of the pod sandboxes matching a filter.
    rpc ListPodSandboxStats(ListPodSandboxStatsRequest) returns (ListPodSandboxStatsResponse) {}

    // UpdateRuntimeConfig updates the runtime configuration based on the given request.
    rpc UpdateRuntimeConfig(UpdateRuntimeConfigRequest) returns (UpdateRuntimeConfigResponse) {}

    // Status returns the status of the runtime.
    rpc Status(StatusRequest) returns (StatusResponse) {}
}

ImageService

跟镜像相关的操作，包括了

  1. 增：PullImage
  2. 查：ListImages、ImageStatus和ImageFsInfo
  3. 删：RemoveImage
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// ImageService defines the public APIs for managing images.
service ImageService {
    // ListImages lists existing images.
    rpc ListImages(ListImagesRequest) returns (ListImagesResponse) {}

    // ImageStatus returns the status of the image. If the image is not
    // present, returns a response with ImageStatusResponse.Image set to
    // nil.
    rpc ImageStatus(ImageStatusRequest) returns (ImageStatusResponse) {}

    // PullImage pulls an image with authentication config.
    rpc PullImage(PullImageRequest) returns (PullImageResponse) {}

    // RemoveImage removes the image.
    // This call is idempotent, and must not return an error if the image has
    // already been removed.
    rpc RemoveImage(RemoveImageRequest) returns (RemoveImageResponse) {}

    // ImageFSInfo returns information of the filesystem that is used to store images.
    rpc ImageFsInfo(ImageFsInfoRequest) returns (ImageFsInfoResponse) {}
}

CRI CLI

CRI 自带了命令行工具 crictl。

Linux 下安装脚本：

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VERSION="v1.26.0" # check latest version in /releases page
wget https://github.com/kubernetes-sigs/cri-tools/releases/download/$VERSION/crictl-$VERSION-linux-amd64.tar.gz
sudo tar zxvf crictl-$VERSION-linux-amd64.tar.gz -C /usr/local/bin
rm -f crictl-$VERSION-linux-amd64.tar.gz