CRI - Container Runtime Interface
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- [Kubernetes架构](concepts/index.md)
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- [Kubernetes架构](concepts/index.md)
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- [Etcd解析](concepts/etcd.md)
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- [Etcd解析](concepts/etcd.md)
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- [开放接口](concepts/open-interfaces.md)
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- [开放接口](concepts/open-interfaces.md)
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- [CRI - Container Runtime Interface(容器运行时接口)](concepts/cri.md)
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- [设计理念](concepts/concepts.md)
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- [设计理念](concepts/concepts.md)
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- [资源对象与基本概念解析](concepts/objects.md)
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- [资源对象与基本概念解析](concepts/objects.md)
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- [Pod](concepts/pod-overview.md)
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- [Pod](concepts/pod-overview.md)
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# CRI - Container Runtime Interface(容器运行时接口)
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CRI中定义了**容器**和**镜像**的服务的接口,因为容器运行时与镜像的生命周期是彼此隔离的,因此需要定义两个服务。该接口使用[Protocol Buffer](https://developers.google.com/protocol-buffers/),基于[gRPC](https://grpc.io/),在kubernetes v1.7+版本中是在[pkg/kubelet/apis/cri/v1alpha1/runtime](https://github.com/kubernetes/kubernetes/tree/master/pkg/kubelet/apis/cri/v1alpha1/runtime)的`api.proto`中定义的。
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## CRI架构
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Container Runtime实现了CRI gRPC Server,包括`RuntimeService`和`ImageService`。该gRPC Server需要监听本地的Unix socket,而kubelet则作为gRPC Client运行。
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![CRI架构-图片来自kubernetes blog](../images/cri-architecture.png)
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## 启用CRI
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除非集成了rktnetes,否则CRI都是被默认启用了,kubernetes1.7版本开始旧的预集成的docker CRI已经被移除。
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要想启用CRI只需要在kubelet的启动参数重传入此参数:`--container-runtime-endpoint`远程运行时服务的端点。当前Linux上支持unix socket,windows上支持tcp。例如:`unix:///var/run/dockershim.sock`、 `tcp://localhost:373`,默认是`unix:///var/run/dockershim.sock`,即默认使用本地的docker作为容器运行时。
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关于CRI的详细进展请参考[CRI: the Container Runtime Interface](https://github.com/kubernetes/community/blob/master/contributors/devel/container-runtime-interface.md)。
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## CRI接口
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Kubernetes1.9中的CRI接口在`api.proto`中的定义如下:
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```protobuf
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// Runtime service defines the public APIs for remote container runtimes
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service RuntimeService {
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// Version returns the runtime name, runtime version, and runtime API version.
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rpc Version(VersionRequest) returns (VersionResponse) {}
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// RunPodSandbox creates and starts a pod-level sandbox. Runtimes must ensure
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// the sandbox is in the ready state on success.
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rpc RunPodSandbox(RunPodSandboxRequest) returns (RunPodSandboxResponse) {}
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// StopPodSandbox stops any running process that is part of the sandbox and
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// reclaims network resources (e.g., IP addresses) allocated to the sandbox.
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// If there are any running containers in the sandbox, they must be forcibly
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// terminated.
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// This call is idempotent, and must not return an error if all relevant
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// resources have already been reclaimed. kubelet will call StopPodSandbox
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// at least once before calling RemovePodSandbox. It will also attempt to
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// reclaim resources eagerly, as soon as a sandbox is not needed. Hence,
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// multiple StopPodSandbox calls are expected.
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rpc StopPodSandbox(StopPodSandboxRequest) returns (StopPodSandboxResponse) {}
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// RemovePodSandbox removes the sandbox. If there are any running containers
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// in the sandbox, they must be forcibly terminated and removed.
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// This call is idempotent, and must not return an error if the sandbox has
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// already been removed.
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rpc RemovePodSandbox(RemovePodSandboxRequest) returns (RemovePodSandboxResponse) {}
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// PodSandboxStatus returns the status of the PodSandbox. If the PodSandbox is not
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// present, returns an error.
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rpc PodSandboxStatus(PodSandboxStatusRequest) returns (PodSandboxStatusResponse) {}
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// ListPodSandbox returns a list of PodSandboxes.
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rpc ListPodSandbox(ListPodSandboxRequest) returns (ListPodSandboxResponse) {}
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// CreateContainer creates a new container in specified PodSandbox
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rpc CreateContainer(CreateContainerRequest) returns (CreateContainerResponse) {}
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// StartContainer starts the container.
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rpc StartContainer(StartContainerRequest) returns (StartContainerResponse) {}
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// StopContainer stops a running container with a grace period (i.e., timeout).
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// This call is idempotent, and must not return an error if the container has
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// already been stopped.
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// TODO: what must the runtime do after the grace period is reached?
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rpc StopContainer(StopContainerRequest) returns (StopContainerResponse) {}
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// RemoveContainer removes the container. If the container is running, the
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// container must be forcibly removed.
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// This call is idempotent, and must not return an error if the container has
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// already been removed.
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rpc RemoveContainer(RemoveContainerRequest) returns (RemoveContainerResponse) {}
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// ListContainers lists all containers by filters.
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rpc ListContainers(ListContainersRequest) returns (ListContainersResponse) {}
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// ContainerStatus returns status of the container. If the container is not
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// present, returns an error.
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rpc ContainerStatus(ContainerStatusRequest) returns (ContainerStatusResponse) {}
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// UpdateContainerResources updates ContainerConfig of the container.
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rpc UpdateContainerResources(UpdateContainerResourcesRequest) returns (UpdateContainerResourcesResponse) {}
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// ExecSync runs a command in a container synchronously.
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rpc ExecSync(ExecSyncRequest) returns (ExecSyncResponse) {}
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// Exec prepares a streaming endpoint to execute a command in the container.
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rpc Exec(ExecRequest) returns (ExecResponse) {}
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// Attach prepares a streaming endpoint to attach to a running container.
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rpc Attach(AttachRequest) returns (AttachResponse) {}
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// PortForward prepares a streaming endpoint to forward ports from a PodSandbox.
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rpc PortForward(PortForwardRequest) returns (PortForwardResponse) {}
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// ContainerStats returns stats of the container. If the container does not
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// exist, the call returns an error.
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rpc ContainerStats(ContainerStatsRequest) returns (ContainerStatsResponse) {}
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// ListContainerStats returns stats of all running containers.
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rpc ListContainerStats(ListContainerStatsRequest) returns (ListContainerStatsResponse) {}
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// UpdateRuntimeConfig updates the runtime configuration based on the given request.
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rpc UpdateRuntimeConfig(UpdateRuntimeConfigRequest) returns (UpdateRuntimeConfigResponse) {}
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// Status returns the status of the runtime.
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rpc Status(StatusRequest) returns (StatusResponse) {}
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}
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// ImageService defines the public APIs for managing images.
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service ImageService {
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// ListImages lists existing images.
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rpc ListImages(ListImagesRequest) returns (ListImagesResponse) {}
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// ImageStatus returns the status of the image. If the image is not
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// present, returns a response with ImageStatusResponse.Image set to
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// nil.
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rpc ImageStatus(ImageStatusRequest) returns (ImageStatusResponse) {}
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// PullImage pulls an image with authentication config.
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rpc PullImage(PullImageRequest) returns (PullImageResponse) {}
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// RemoveImage removes the image.
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// This call is idempotent, and must not return an error if the image has
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// already been removed.
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rpc RemoveImage(RemoveImageRequest) returns (RemoveImageResponse) {}
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// ImageFSInfo returns information of the filesystem that is used to store images.
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rpc ImageFsInfo(ImageFsInfoRequest) returns (ImageFsInfoResponse) {}
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}
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```
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这其中包含了两个gRPC服务:
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- **RuntimeService**:容器和Sandbox运行时管理
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- **ImageService**:提供了从镜像仓库拉取、查看、和移除镜像的RPC。
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## 当前支持的CRI后端
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我们最初在使用Kubernetes时通常会默认使用Docker作为容器运行时,其实从Kubernetes1.5开始已经开始支持CRI,目前是处于Alpha版本,通过CRI接口可以指定使用其它容器运行时作为Pod的后端,目前支持CNI的后端有:
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- [cri-o](https://github.com/kubernetes-incubator/cri-o):同时兼容OCI和CRI的容器运行时
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- [cri-containerd](https://github.com/containerd/cri-containerd):基于[Containerd](https://github.com/containerd/containerd)的Kubernetes CNI实现
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- [rkt](https://coreos.com/rkt/):由于CoreOS主推的用来跟docker抗衡的容器运行时
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- [frakti](https://github.com/kubernetes/frakti):基于hypervisor的CRI
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- [docker](https://www.docker.com):kuberentes最初就开始支持的容器运行时,目前还没完全从kubelet中解耦,docker公司同时推广了[OCI](https://www.opencontainers.org/)标准
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- [clear-containers](https://github.com/clearcontainers):由Intel推出的同时兼容OCI和CRI的容器运行时
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- [kata-containers](https://katacontainers.io/):符合OCI规范同时兼容CRI
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CRI是由[SIG-Node](https://kubernetes.slack.com/archives/sig-node)来维护的。
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## 参考
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- [Kubernetes CRI and Minikube](https://sreeninet.wordpress.com/2017/02/11/kubernetes-cri-and-minikube/)
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- [Kubernetes container runtime interface](https://feisky.xyz/2016/09/24/Kubernetes-container-runtime-interface/)
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- [CRI-O and Alternative Runtimes in Kubernetes](https://www.projectatomic.io/blog/2017/02/crio-runtimes/)
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- [Docker、Containerd、RunC...:你应该知道的所有](http://www.infoq.com/cn/news/2017/02/Docker-Containerd-RunC)
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- [Introducing Container Runtime Interface (CRI) in Kubernetes](http://blog.kubernetes.io/2016/12/container-runtime-interface-cri-in-kubernetes.html)
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