containerd基本使用

发表于 2023-10-24 更新于 2024-08-08

containerd是一个容器运行时标准,也是k8s目前主流的运行时，本文介绍历史，存储方式，和oci

containerd历史

containerd是一个运行时，最开始集成在docker中拆解出来捐赠给cncf，同样被拆解出来的还有runc，以及根据docker镜像v2制定的oci镜像规范

1.24版本之前k8s的kubelet内置了dokcer-shim插件负责和docker通讯，之后则只能通过cri

flowchart LR
  kubelet(kubelet)-->docker-shim(docker-shim)
  docker-shim(docker-shim)-->docker(docker)
  docker(docker)-->containers([containers])

最开始cri是一个单独的进程,然后发现效率太差

flowchart LR
  kubelet(kubelet)--"grpc"-->cri-plugin(cri-plugin)

  cri-plugin(cri-plugin)--"grpc"-->containerd(containerd)

  containerd(containerd)--"exec"-->containerd-shim-runc(containerd-shim-runc)
  containerd-shim-runc(containerd-shim-runc)--"exec"-->runc(runc)
  runc(runc)--"exec"-->containers([containers])

最后将cri已插件的形式集成到containerd中

flowchart LR
  kubelet(kubelet)--"grpc"-->cri-plugin(cri-plugin)

  subgraph containerd组件
  cri-plugin(cri-plugin)-->containerd(containerd)
  end

  containerd(containerd)--"exec"-->containerd-shim-runc(containerd-shim-runc)
  containerd-shim-runc(containerd-shim-runc)--"exec"-->runc(runc)
  runc(runc)--"exec"-->containers([containers])

架构

全局架构

Alt text

containerd与kubelet

Alt text

内部插件架构

Alt text

flowchart LR
  kubectl(kubctl)<-->api-server(api-server)

  subgraph master
  api-server(api-server)<-->etcd[(etcd)]
  api-server(api-server)<-->scheduler(scheduler)
  api-server(api-server)<-->controller-manage(controller-manage)
  end

  api-server(api-server)<-->kubelet(kubelet)
  kubelet(kubelet)<--"grpc"-->containerd(containerd)

  subgraph containerd组件
  containerd(containerd)<--"exec"-->containerd-shim-runc(containerd-shim-runc)
  containerd-shim-runc(containerd-shim-runc)<--"exec"-->runc(runc)
  runc(runc)<--"exec"-->containers(containers)
  end

  api-server(api-server)<-->kube-proxy(kube-proxy)
  kube-proxy(kube-proxy)<-->ipt(iptables/ipvs)

containerd下载安装

docker官方打包的rpm地址
官方仓库下载https://github.com/containerd/containerd/releases
一般安装docker的时候自动安装

ctr使用

containerd可以使用的客户端有很多比如crictl，nerdctl命令

–address value, -a value 指定 containerd’s GRPC server，默认 /run/containerd/containerd.sock
查看K8S命名空间下的镜像,-n指定namespace

ctr -n k8s.io images ls

查看所有namespace

ctr ns ls

下载镜像

ctr images pull docker.io/library/alpine:3.18.3

创建 container

ctr c create docker.io/library/alpine:3.18.3 alpine

查看

ctr c ls

后台启动

ctr t start -d alpine

查看container

ctr t ls

查看 k8s 中正在运行的容器

ctr -n k8s.io task ls

打tag

ctr images tag docker.io/library/alpine:3.18.3 <仓库>/alpine:3.18.3

push 上传镜像

ctr images push <镜像>

查看插件

ctr plugin ls

打印containerd默认配置

containerd config default

OCI镜像格式

各个类型的关系

oci镜像格式的mediaType参考这里

Alt text

类型mediaType

所有例子基于alpine:3.18.3

index

最顶级的类型主要存放各个操作系统和平台对应的manifest类型

例子

{
    "manifests": [
        {
            "digest": "sha256:c5c5fda71656f28e49ac9c5416b3643eaa6a108a8093151d6d1afc9463be8e33",
            "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
            "platform": {
                "architecture": "amd64",
                "os": "linux"
            },
            "size": 528
        },
        {
            "digest": "sha256:f748290eb66ad6f938e25dd348acfb3527a422e280b7547b1cdfaf38d4492c4b",
            "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
            "platform": {
                "architecture": "arm",
                "os": "linux",
                "variant": "v6"
            },
            "size": 528
        },
        {
            "digest": "sha256:16e86b2388774982fbdf230101a72201691b1f97cb0066c2099abf30dd7e6d59",
            "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
            "platform": {
                "architecture": "arm",
                "os": "linux",
                "variant": "v7"
            },
            "size": 528
        },
        {
            "digest": "sha256:b312e4b0e2c665d634602411fcb7c2699ba748c36f59324457bc17de485f36f6",
            "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
            "platform": {
                "architecture": "arm64",
                "os": "linux",
                "variant": "v8"
            },
            "size": 528
        },
        {
            "digest": "sha256:1fd62556954250bac80d601a196bb7fd480ceba7c10e94dd8fd4c6d1c08783d5",
            "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
            "platform": {
                "architecture": "386",
                "os": "linux"
            },
            "size": 528
        },
        {
            "digest": "sha256:c75ede79e457d6454bca6fc51967a247a4b9daff9f31197cfbef69b1a651cada",
            "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
            "platform": {
                "architecture": "ppc64le",
                "os": "linux"
            },
            "size": 528
        },
        {
            "digest": "sha256:5febc00b4d2a84af2a077bc34ea90659b6570110a54253f19c5dca8164b1dbf6",
            "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
            "platform": {
                "architecture": "s390x",
                "os": "linux"
            },
            "size": 528
        }
    ],
    "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
    "schemaVersion": 2
}

manifest

主要定义镜像相关的清单，主要包含config类型和layers类型

{
  "schemaVersion": 2,
  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  "config": {
    "mediaType": "application/vnd.docker.container.image.v1+json",
    "size": 1471,
    "digest": "sha256:7e01a0d0a1dcd9e539f8e9bbd80106d59efbdf97293b3d38f5d7a34501526cdb"
  },
  "layers": [
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "size": 3401613,
      "digest": "sha256:7264a8db6415046d36d16ba98b79778e18accee6ffa71850405994cffa9be7de"
    }
  ]
}

config

记录镜像的历史，启动参数环境变量以及最重要的解压后的层等信息

例子

{
    "architecture": "amd64",
    "config": {
        "Hostname": "",
        "Domainname": "",
        "User": "",
        "AttachStdin": false,
        "AttachStdout": false,
        "AttachStderr": false,
        "Tty": false,
        "OpenStdin": false,
        "StdinOnce": false,
        "Env": [
            "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
        ],
        "Cmd": [
            "/bin/sh"
        ],
        "Image": "sha256:39dfd593e04b939e16d3a426af525cad29b8fc7410b06f4dbad8528b45e1e5a9",
        "Volumes": null,
        "WorkingDir": "",
        "Entrypoint": null,
        "OnBuild": null,
        "Labels": null
    },
    "container": "ba09fe2c8f99faad95871d467a22c96f4bc8166bd01ce0a7c28dd5472697bfd1",
    "container_config": {
        "Hostname": "ba09fe2c8f99",
        "Domainname": "",
        "User": "",
        "AttachStdin": false,
        "AttachStdout": false,
        "AttachStderr": false,
        "Tty": false,
        "OpenStdin": false,
        "StdinOnce": false,
        "Env": [
            "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
        ],
        "Cmd": [
            "/bin/sh",
            "-c",
            "#(nop) ",
            "CMD [\"/bin/sh\"]"
        ],
        "Image": "sha256:39dfd593e04b939e16d3a426af525cad29b8fc7410b06f4dbad8528b45e1e5a9",
        "Volumes": null,
        "WorkingDir": "",
        "Entrypoint": null,
        "OnBuild": null,
        "Labels": {}
    },
    "created": "2023-08-07T19:20:20.894140623Z",
    "docker_version": "20.10.23",
    "history": [
        {
            "created": "2023-08-07T19:20:20.71894984Z",
            "created_by": "/bin/sh -c #(nop) ADD file:32ff5e7a78b890996ee4681cc0a26185d3e9acdb4eb1e2aaccb2411f922fed6b in / "
        },
        {
            "created": "2023-08-07T19:20:20.894140623Z",
            "created_by": "/bin/sh -c #(nop)  CMD [\"/bin/sh\"]",
            "empty_layer": true
        }
    ],
    "os": "linux",
    "rootfs": {
        "type": "layers",
        "diff_ids": [
            "sha256:4693057ce2364720d39e57e85a5b8e0bd9ac3573716237736d6470ec5b7b7230"
        ]
    }
}

layer

记录压缩过后的层sha256信息,是真正层的内容一般采用tar.gz压缩

下载保存oci镜像格式

使用skopeo可以和方便的保存到本地，之前介绍过使用skopeo同步docker镜像

skopeo copy docker://docker.io/alpine:3.18.3 oci:alpine-oci --override-os linux --override-arch amd64

❯ tree                                                                   
.
├── blobs
│   └── sha256
│       ├── 7264a8db6415046d36d16ba98b79778e18accee6ffa71850405994cffa9be7de
│       ├── 913cf3a39d377faf89ed388ad913a318a390488c9f34c46e43424795cdabffe8
│       └── cf4e5bc0709f07284518b287f570c47bdb2afc14b8ae4f14077e9ff810a0120b
├── index.json
└── oci-layout

3 directories, 5 files

Containerd存储方式

目录结构

其目录命名格式以类型.id的格式
有些目录根据插件并没有显示
默认数据存放在/var/lib/containerd/中

tree -L 2
.
├── io.containerd.content.v1.content # 存放从hub上下载的源文件
│   ├── blobs                        # 存放下载完毕的文件
│   └── ingest                       # 存放下载未完成的文件
├── io.containerd.grpc.v1.cri        # cri插件存放的文件
│   ├── containers                   # cri创建的容器
│   └── sandboxes
├── io.containerd.metadata.v1.bolt   # 存放containerd的数据文件
│   └── meta.db           
├── io.containerd.runtime.v1.linux
├── io.containerd.runtime.v2.task    # 运行的容器
│   └── k8s.io                       # namespace
├── io.containerd.snapshotter.v1.native
│   └── snapshots
├── io.containerd.snapshotter.v1.overlayfs # 存放解压过后的文件
│   ├── metadata.db                        # 解压数据库文件
│   └── snapshots                          # 解压的文件
└── tmpmounts                              # 临时挂载目录

15 directories, 2 files

参考

https://blog.frognew.com/2021/04/relearning-container-01.html