kubernetes-handbook/concepts/cri.md

141 lines
8.8 KiB
Markdown
Raw Blame History

This file contains ambiguous Unicode characters!

This file contains ambiguous Unicode characters that may be confused with others in your current locale. If your use case is intentional and legitimate, you can safely ignore this warning. Use the Escape button to highlight these characters.

# CRI - Container Runtime Interface容器运行时接口
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。
## CRI架构
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。
![CRI架构-图片来自kubernetes blog](../images/cri-architecture.png)
## 启用CRI
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。
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 socketwindows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。
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)。
## CRI接口
Kubernetes1.9中的CRI接口在`api.proto`中的定义如下:
```protobuf
// 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.
// TODO: what must the runtime do 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) {}
// 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) {}
// 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 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) {}
}
```
这其中包含了两个gRPC服务
- **RuntimeService**容器和Sandbox运行时管理
- **ImageService**提供了从镜像仓库拉取、查看、和移除镜像的RPC。
## 当前支持的CRI后端
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 CRI 的后端有:
- [cri-o](https://github.com/kubernetes-incubator/cri-o)同时兼容OCI和CRI的容器运行时
- [cri-containerd](https://github.com/containerd/cri-containerd):基于[Containerd](https://github.com/containerd/containerd)的Kubernetes CRI 实现
- [rkt](https://coreos.com/rkt/)由于CoreOS主推的用来跟docker抗衡的容器运行时
- [frakti](https://github.com/kubernetes/frakti)基于hypervisor的CRI
- [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
- [clear-containers](https://github.com/clearcontainers)由Intel推出的同时兼容OCI和CRI的容器运行时
- [kata-containers](https://katacontainers.io/)符合OCI规范同时兼容CRI
CRI是由[SIG-Node](https://kubernetes.slack.com/archives/sig-node)来维护的。
## 参考
- [Kubernetes CRI and Minikube](https://sreeninet.wordpress.com/2017/02/11/kubernetes-cri-and-minikube/)
- [Kubernetes container runtime interface](https://feisky.xyz/2016/09/24/Kubernetes-container-runtime-interface/)
- [CRI-O and Alternative Runtimes in Kubernetes](https://www.projectatomic.io/blog/2017/02/crio-runtimes/)
- [Docker、Containerd、RunC...:你应该知道的所有](http://www.infoq.com/cn/news/2017/02/Docker-Containerd-RunC)
- [Introducing Container Runtime Interface (CRI) in Kubernetes](http://blog.kubernetes.io/2016/12/container-runtime-interface-cri-in-kubernetes.html)