Docker 公司从 2013 年发布容器引擎 Docker 后，就被全球开发者使用并不断改进它的功能。随着容器标准的建立，Docker 引擎架构也从单体走向微服务结构，剥离出 dontainerd 引擎。它在整个容器技术架构中的位置如下：

图 6-1 containerd 架构图，版权源自 https://containerd.io/

containerd 使用初体验

从官方仓库可以下载最新的 containerd 可执行文件，因为依赖 runc，所以需要一并下载才能正常使用：

# 下载 containerd 二进制文件
wget -q --show-progress --https-only --timestamping \
  https://github.com/opencontainers/runc/releases/download/v1.0.0-rc10/runc.amd64 \
  https://github.com/containerd/containerd/releases/download/v1.3.4/containerd-1.3.4.linux-amd64.tar.gz \
  https://github.com/kubernetes-sigs/cri-tools/releases/download/v1.18.0/crictl-v1.18.0-linux-amd64.tar.gz
sudo mv runc.amd64 runc

# 安装二进制文件
tar -xvf crictl-v1.18.0-linux-amd64.tar.gz
chmod +x crictl runc
sudo cp crictl runc /usr/local/bin/
mkdir containerd
tar -xvf containerd-1.3.4.linux-amd64.tar.gz -C containerd
sudo cp containerd/bin/* /bin/

containerd 提供了默认的配置文件 config.toml，默认放在 /etc/containerd/config.toml：

[plugins]
  [plugins.cri.containerd]
    snapshotter = "overlayfs"
    [plugins.cri.containerd.default_runtime]
      runtime_type = "io.containerd.runtime.v1.linux"
      runtime_engine = "/usr/local/bin/runc"
      runtime_root = ""

containerd 服务一般采用后台守护进程方式运行，在 Linux 中使用 systemd 运行：

# 配置 containerd.service
sudo cat <<EOF | sudo tee /etc/systemd/system/containerd.service
[Unit]
Description=containerd container runtime
Documentation=https://containerd.io
After=network.target
[Service]
ExecStartPre=/sbin/modprobe overlay
ExecStart=/bin/containerd
Restart=always
RestartSec=5
Delegate=yes
KillMode=process
OOMScoreAdjust=-999
LimitNOFILE=1048576
LimitNPROC=infinity
LimitCORE=infinity
[Install]
WantedBy=multi-user.target
EOF

#启动
sudo systemctl daemon-reload
sudo systemctl enable containerd
sudo systemctl start containerd

#配置 crictl 客户端
sudo crictl config runtime-endpoint unix:///var/run/containerd/containerd.sock

至此，containerd 的使用流程就体验完成了。

通过客户端深入了解 containerd

containerd 启动后，我们需要使用客户端命令行工具来了解下容器运行的情况。这个时候，我们手上有 2 个工具可以使用。一个是 crictl 这个是 Kubernetes 社区提供的操作容器接口标准的客户端工具，另外一个是 ctr 这是 containerd 自带的客户端工具，ctr 是测试使用的工具，在日常工作中推荐使用 crictl 工具来管理容器。

ctr 工具运行如下：

   ctr - 
        __
  _____/ /______
 / ___/ __/ ___/
/ /__/ /_/ /
\___/\__/_/

containerd CLI

USAGE:
   ctr [global options] command [command options] [arguments...]

VERSION:
   v1.3.4

DESCRIPTION:
ctr is an unsupported debug and administrative client for interacting
with the containerd daemon. Because it is unsupported, the commands,
options, and operations are not guaranteed to be backward compatible or
stable from release to release of the containerd project.

COMMANDS:
   plugins, plugin            provides information about containerd plugins
   version                    print the client and server versions
   containers, c, container   manage containers
   content                    manage content
   events, event              display containerd events
   images, image, i           manage images
   leases                     manage leases
   namespaces, namespace, ns  manage namespaces
   pprof                      provide golang pprof outputs for containerd
   run                        run a container
   snapshots, snapshot        manage snapshots
   tasks, t, task             manage tasks
   install                    install a new package
   shim                       interact with a shim directly
   help, h                    Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --debug                      enable debug output in logs
   --address value, -a value    address for containerd's GRPC server (default: "/run/contai
nerd/containerd.sock")
   --timeout value              total timeout for ctr commands (default: 0s)
   --connect-timeout value      timeout for connecting to containerd (default: 0s)
   --namespace value, -n value  namespace to use with commands (default: "default") [$CONTA
INERD_NAMESPACE]
   --help, -h                   show help
   --version, -v                print the version

crictl 运行命令如下：

NAME:
   crictl - client for CRI

USAGE:
   crictl [global options] command [command options] [arguments...]

VERSION:
   v1.18.0

COMMANDS:
   attach              Attach to a running container
   create              Create a new container
   exec                Run a command in a running container
   version             Display runtime version information
   images, image, img  List images
   inspect             Display the status of one or more containers
   inspecti            Return the status of one or more images
   imagefsinfo         Return image filesystem info
   inspectp            Display the status of one or more pods
   logs                Fetch the logs of a container
   port-forward        Forward local port to a pod
   ps                  List containers
   pull                Pull an image from a registry
   run                 Run a new container inside a sandbox
   runp                Run a new pod
   rm                  Remove one or more containers
   rmi                 Remove one or more images
   rmp                 Remove one or more pods
   pods                List pods
   start               Start one or more created containers
   info                Display information of the container runtime
   stop                Stop one or more running containers
   stopp               Stop one or more running pods
   update              Update one or more running containers
   config              Get and set crictl options
   inspecti            Return the status of one or more images
   imagefsinfo         Return image filesystem info
   inspectp            Display the status of one or more pods
   logs                Fetch the logs of a container
   port-forward        Forward local port to a pod
   ps                  List containers
   pull                Pull an image from a registry
   run                 Run a new container inside a sandbox
   runp                Run a new pod
   rm                  Remove one or more containers
   rmi                 Remove one or more images
   rmp                 Remove one or more pods
   pods                List pods
   start               Start one or more created containers
   info                Display information of the container runtime
   stop                Stop one or more running containers
   stopp               Stop one or more running pods
   update              Update one or more running containers
   config              Get and set crictl options
   stats               List container(s) resource usage statistics
   completion          Output shell completion code
   help, h             Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --config value, -c value            Location of the client config file. If not specified
 and the default does not exist, the program's directory is searched as well (default: "/et
c/crictl.yaml") [$CRI_CONFIG_FILE]
   --debug, -D                         Enable debug mode (default: false)
   --image-endpoint value, -i value    Endpoint of CRI image manager service [$IMAGE_SERVIC
E_ENDPOINT]
   --runtime-endpoint value, -r value  Endpoint of CRI container runtime service (default: 
"unix:///var/run/dockershim.sock") [$CONTAINER_RUNTIME_ENDPOINT]
   --timeout value, -t value           Timeout of connecting to the server (default: 2s)
   --help, -h                          show help (default: false)
   --version, -v                       print the version (default: false)

从 2 个命令参数对比参照可以得知，crictl 的功能是比 ctr 要丰富很多的。为了日常使用方便，这里我把 crictl 和 Docker 命令做一个对比，方便大家参照使用：

注意：上传镜像功能属于和镜像仓库服务的交互，crictl 没有提供此功能可以减轻不少代码逻辑负担。

看到以上清单，cotnainerd 和 Docker 的功能是一脉相承。因此在生产环境使用 containerd 可以减少很多调用依赖。

Docker 作为 K8s 容器运行时，调用关系如下：

kubelet --> docker shim （在 kubelet 进程中） --> dockerd --> containerd

Containerd 作为 K8s 容器运行时，调用关系如下：

kubelet --> cri plugin（在 containerd 进程中） --> containerd

dockerd 是 Docker 原生容器应用引擎提供的代理服务，内置了 swarm cluster、docker build、docker push、docker api 等扩展功能，但是在生产环境默认都是 Kubernetes 集群环境，所以这块的功能可以直接去掉。

对于 Docker 容器日志、网络配置

日志对比

CNI 网络对比

总结

containerd 是 Docker 容器落地实践过程中标准化的产物，经过了全球无数企业应用场景的锤炼。所以它的稳定性是值得开发者信赖的工具。虽然当前业界对 Docker 公司的产品采取回避策略，但是 containerd 是当前最佳的生产环境的容器引擎，值得继续关注场景的使用和支持。