描述: 事实上，Docker 和 Containerd 是可以同时使用的，只不过 Docker 默认使用的 Containerd 的命名空间不是 default，而是 moby，此处为了更方便我们学习可以将 Docker 与 Containerd 联合使用。

Step 1.安装配置 containerd

yum install -y yum-utils
yum-config-manager --add-repo http://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo
yum makecache fast

yum -y install containerd.io

# cat /etc/containerd/config.toml
disabled_plugins = []
imports = []
oom_score = 0
plugin_dir = ""
required_plugins = []
root = "/var/lib/containerd"
state = "/run/containerd"
temp = ""
version = 2

[cgroup]
  path = ""

[debug]
  address = ""
  format = ""
  gid = 0
  level = ""
  uid = 0

[grpc]
  address = "/run/containerd/containerd.sock"
  gid = 0
  max_recv_message_size = 16777216
  max_send_message_size = 16777216
  tcp_address = ""
  tcp_tls_ca = ""
  tcp_tls_cert = ""
  tcp_tls_key = ""
  uid = 0

[metrics]
  address = ""
  grpc_histogram = false

[plugins]

  [plugins."io.containerd.gc.v1.scheduler"]
    deletion_threshold = 0
    mutation_threshold = 100
    pause_threshold = 0.02
    schedule_delay = "0s"
    startup_delay = "100ms"

  [plugins."io.containerd.grpc.v1.cri"]
    device_ownership_from_security_context = false
    disable_apparmor = false
    disable_cgroup = false
    disable_hugetlb_controller = true
    disable_proc_mount = false
    disable_tcp_service = true
    enable_selinux = false
    enable_tls_streaming = false
    enable_unprivileged_icmp = false
    enable_unprivileged_ports = false
    ignore_image_defined_volumes = false
    max_concurrent_downloads = 3
    max_container_log_line_size = 16384
    netns_mounts_under_state_dir = false
    restrict_oom_score_adj = false
    sandbox_image = "registry.cn-hangzhou.aliyuncs.com/google_containers/pause:3.6"
    selinux_category_range = 1024
    stats_collect_period = 10
    stream_idle_timeout = "4h0m0s"
    stream_server_address = "127.0.0.1"
    stream_server_port = "0"
    systemd_cgroup = false
    tolerate_missing_hugetlb_controller = true
    unset_seccomp_profile = ""

    [plugins."io.containerd.grpc.v1.cri".cni]
      bin_dir = "/opt/cni/bin"
      conf_dir = "/etc/cni/net.d"
      conf_template = ""
      ip_pref = ""
      max_conf_num = 1

    [plugins."io.containerd.grpc.v1.cri".containerd]
      default_runtime_name = "runc"
      disable_snapshot_annotations = false
      discard_unpacked_layers = false
      ignore_rdt_not_enabled_errors = false
      no_pivot = false
      snapshotter = "stargz"

      [plugins."io.containerd.grpc.v1.cri".containerd.default_runtime]
        base_runtime_spec = ""
        cni_conf_dir = ""
        cni_max_conf_num = 0
        container_annotations = []
        pod_annotations = []
        privileged_without_host_devices = false
        runtime_engine = ""
        runtime_path = ""
        runtime_root = ""
        runtime_type = ""

        [plugins."io.containerd.grpc.v1.cri".containerd.default_runtime.options]

      [plugins."io.containerd.grpc.v1.cri".containerd.runtimes]

        [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc]
          base_runtime_spec = ""
          cni_conf_dir = ""
          cni_max_conf_num = 0
          container_annotations = []
          pod_annotations = []
          privileged_without_host_devices = false
          runtime_engine = ""
          runtime_path = ""
          runtime_root = ""
          runtime_type = "io.containerd.runc.v2"

          [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc.options]
            BinaryName = ""
            CriuImagePath = ""
            CriuPath = ""
            CriuWorkPath = ""
            IoGid = 0
            IoUid = 0
            NoNewKeyring = false
            NoPivotRoot = false
            Root = ""
            ShimCgroup = ""
            SystemdCgroup = true

      [plugins."io.containerd.grpc.v1.cri".containerd.untrusted_workload_runtime]
        base_runtime_spec = ""
        cni_conf_dir = ""
        cni_max_conf_num = 0
        container_annotations = []
        pod_annotations = []
        privileged_without_host_devices = false
        runtime_engine = ""
        runtime_path = ""
        runtime_root = ""
        runtime_type = ""

        [plugins."io.containerd.grpc.v1.cri".containerd.untrusted_workload_runtime.options]

    [plugins."io.containerd.grpc.v1.cri".image_decryption]
      key_model = "node"

    [plugins."io.containerd.grpc.v1.cri".registry]
      config_path = ""

      [plugins."io.containerd.grpc.v1.cri".registry.auths]

      [plugins."io.containerd.grpc.v1.cri".registry.configs]

      [plugins."io.containerd.grpc.v1.cri".registry.headers]

      [plugins."io.containerd.grpc.v1.cri".registry.mirrors]
        [plugins."io.containerd.grpc.v1.cri".registry.mirrors."docker.io"]
            endpoint = ["https://docker.mirrors.ustc.edu.cn","http://hub-mirror.c.163.com"]
        [plugins."io.containerd.grpc.v1.cri".registry.mirrors."gcr.io"]
            endpoint = ["https://gcr.mirrors.ustc.edu.cn"]
        [plugins."io.containerd.grpc.v1.cri".registry.mirrors."k8s.gcr.io"]
            endpoint = ["https://gcr.mirrors.ustc.edu.cn/google-containers/"]
        [plugins."io.containerd.grpc.v1.cri".registry.mirrors."quay.io"]
            endpoint = ["https://quay.mirrors.ustc.edu.cn"]

    [plugins."io.containerd.grpc.v1.cri".x509_key_pair_streaming]
      tls_cert_file = ""
      tls_key_file = ""

  [plugins."io.containerd.internal.v1.opt"]
    path = "/opt/containerd"

  [plugins."io.containerd.internal.v1.restart"]
    interval = "10s"

  [plugins."io.containerd.internal.v1.tracing"]
    sampling_ratio = 1.0
    service_name = "containerd"

  [plugins."io.containerd.metadata.v1.bolt"]
    content_sharing_policy = "shared"

  [plugins."io.containerd.monitor.v1.cgroups"]
    no_prometheus = false

  [plugins."io.containerd.runtime.v1.linux"]
    no_shim = false
    runtime = "runc"
    runtime_root = ""
    shim = "containerd-shim"
    shim_debug = false

  [plugins."io.containerd.runtime.v2.task"]
    platforms = ["linux/amd64"]
    sched_core = false

  [plugins."io.containerd.service.v1.diff-service"]
    default = ["walking"]

  [plugins."io.containerd.service.v1.tasks-service"]
    rdt_config_file = ""

  [plugins."io.containerd.snapshotter.v1.aufs"]
    root_path = ""

  [plugins."io.containerd.snapshotter.v1.btrfs"]
    root_path = ""

  [plugins."io.containerd.snapshotter.v1.devmapper"]
    async_remove = false
    base_image_size = ""
    discard_blocks = false
    fs_options = ""
    fs_type = ""
    pool_name = ""
    root_path = ""

  [plugins."io.containerd.snapshotter.v1.native"]
    root_path = ""

  [plugins."io.containerd.snapshotter.v1.overlayfs"]
    root_path = ""
    upperdir_label = false

  [plugins."io.containerd.snapshotter.v1.zfs"]
    root_path = ""

  [plugins."io.containerd.tracing.processor.v1.otlp"]
    endpoint = ""
    insecure = false
    protocol = ""

[proxy_plugins]
  [proxy_plugins.stargz]
    type = "snapshot"
    address = "/run/containerd-stargz-grpc/containerd-stargz-grpc.sock"

[stream_processors]

  [stream_processors."io.containerd.ocicrypt.decoder.v1.tar"]
    accepts = ["application/vnd.oci.image.layer.v1.tar+encrypted"]
    args = ["--decryption-keys-path", "/etc/containerd/ocicrypt/keys"]
    env = ["OCICRYPT_KEYPROVIDER_CONFIG=/etc/containerd/ocicrypt/ocicrypt_keyprovider.conf"]
    path = "ctd-decoder"
    returns = "application/vnd.oci.image.layer.v1.tar"

  [stream_processors."io.containerd.ocicrypt.decoder.v1.tar.gzip"]
    accepts = ["application/vnd.oci.image.layer.v1.tar+gzip+encrypted"]
    args = ["--decryption-keys-path", "/etc/containerd/ocicrypt/keys"]
    env = ["OCICRYPT_KEYPROVIDER_CONFIG=/etc/containerd/ocicrypt/ocicrypt_keyprovider.conf"]
    path = "ctd-decoder"
    returns = "application/vnd.oci.image.layer.v1.tar+gzip"

[timeouts]
  "io.containerd.timeout.bolt.open" = "0s"
  "io.containerd.timeout.shim.cleanup" = "5s"
  "io.containerd.timeout.shim.load" = "5s"
  "io.containerd.timeout.shim.shutdown" = "3s"
  "io.containerd.timeout.task.state" = "2s"

[ttrpc]
  address = ""
  gid = 0
  uid = 0

systemctl start containerd  && systemctl enable containerd  && systemctl status containerd

Step 2.在宿主机中安装docker客户端及服务

yum install -y yum-utils
yum-config-manager --add-repo http://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo
yum makecache fast

yum -y install docker-ce

tee /etc/docker/daemon.json <<-'EOF'
{
    "live-restore": true,
    "registry-mirrors": ["https://hub-mirror.c.163.com","https://bmtrgdvx.mirror.aliyuncs.com","https://y9lmbx5j.mirror.aliyuncs.com"],
    "log-driver":"json-file",
    "log-opts":{
        "max-size" :"50m",
        "max-file":"3"
    }
}
EOF

Step 3.编辑/etc/systemd/system/multi-user.target.wants/docker.service文件并为其新增 --containerd如下启动项：--containerd /run/containerd/containerd.sock

vim /etc/systemd/system/multi-user.target.wants/docker.service
ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock --cri-containerd --debug

# - 重新加载配置
systemctl daemon-reload

systemctl enable docker && systemctl start docker && systemctl status docker

Step 4.打开两个Shell终端一个采用 docker 运行一个 busybox 容器，另外一个查看对比。

$ docker run --rm -it busybox sh
  # / # ip addr
  # 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1000
  #     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
  #     inet 127.0.0.1/8 scope host lo
  #       valid_lft forever preferred_lft forever
  # 8: eth0@if9: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue
  #     link/ether 02:42:ac:11:00:02 brd ff:ff:ff:ff:ff:ff
  #     inet 172.17.0.2/16 brd 172.17.255.255 scope global eth0   # 关键点
  #       valid_lft forever preferred_lft forever
  # / # cat /etc/hosts
  # 127.0.0.1       localhost
  # 172.17.0.2      51dcdf68d3b8

# 采用 ctr 在 moby 名称空间下查看docker创建的容器以及Task PID
$ ctr -n moby c ls
  # CONTAINER                                                           IMAGE    RUNTIME
  # 51dcdf68d3b8bf4c9707c9059e33f9570cb83725355595e77cf433dd3e25b64b    -        io.containerd.runc.v2
$ ctr -n moby t ls
  # TASK                                                                PID       STATUS
  # 51dcdf68d3b8bf4c9707c9059e33f9570cb83725355595e77cf433dd3e25b64b    131926    RUNNING

# 验证获取到的 Task PID 下其 net 相关信息
$ grep "172.17.0.2" /proc/131926/net/fib_trie
  |-- 172.17.0.2
  |-- 172.17.0.2

# 采用 ctr 进入 Docker 创建的容器
$ ctr -n moby t exec -t --exec-id $RANDOM  51dcdf68d3b8bf4c9707c9059e33f9570cb83725355595e77cf433dd3e25b64b sh
  # / # ip addr | grep "172.17.0.2"
  #   inet 172.17.0.2/16 brd 172.17.255.255 scope global eth0
  # / # hostname
  #   51dcdf68d3b8

Tips : containerd 引入了 namespace 概念, 每个image和container都会在各自的namespace下可见, 目前k8s会使用 k8s.io 以及 default 作为命名空间。

Tips : 当导入本地镜像时ctr不支持压缩。

Tips : 通过ctr containers create创建容器后，只是一个静态的容器，容器中的用户进程并没有启动，所以还需要通过ctr task start来启动容器进程。 当然也可以用ctr run的命令直接创建并运行容器。在进入容器操作时与docker不同的是，必须在ctr task exec命令后指定--exec-id参数，这个id可以随便写只要唯一就行。

Tips : ctr没有stop容器的功能，只能暂停（ctr task pause）或者杀死（ctr task kill）容器