Containerd, Docker, Kubernetesの関係について

コンテナについて3つのキーワード containerd, docker, kubernetes がややこしいのでここで簡単に整理します。


ランタイムである containerd の役割は、指定されたコンテナイメージからコンテナを稼働することであり、ポート指定や自動起動などの条件設定は出来ません。

Docker (Swarm)Kubernetes は、複数の物理的なマシンを相互に結びつけ、それらを一つの巨大なシステム(クラスター)として効率的に運用することを目的としています。

Docker (Swarm)Kubernetes では、 containerd では定義できない、より細かい条件を付与することにより、複数のコンテナから構成される最小のシステム(ポッド)が、より大きなシステムであるワーカーノードに効率的に配備されます。



管理用のノード (Control Plane) とワーカーノード。ワーカーノードには様々なポッドが配備されます。


containerd のクライアントである ctr は、docker インストール時に既にインストールされています。単一のコンテナを稼働するだけであれば、ctr によるコマンドだけでもコンテナの稼働は可能です。


$ sudo ctr image pull
$ sudo ctr run --net-host nginx
ctl + c で終了

$ sudo ctr c list
CONTAINER    IMAGE                             RUNTIME                  
nginx    io.containerd.runc.v2

namespace リスト

$ sudo ctr ns ls

namespace を指定してコンテナをリストアップ

$ sudo ctr -n moby c ls
CONTAINER                                                           IMAGE    RUNTIME                  
9f2381fa65ea9cf4b445466182a0b71cd088d30e01fcad25dcb062f0d6f59aef    -        io.containerd.runc.v2  


$ sudo ctr i ls
REF                            TYPE                                                      DIGEST                                                                  SIZE     PLATFORMS                                                                                               LABELS application/vnd.docker.distribution.manifest.list.v2+json sha256:0b970013351304af46f322da1263516b188318682b2ab1091862497591189ff1 54.1 MiB linux/386,linux/amd64,linux/arm/v5,linux/arm/v7,linux/arm64/v8,linux/mips64le,linux/ppc64le,linux/s390x -      


$ ctr --help
   ctr - 
  _____/ /______
 / ___/ __/ ___/
/ /__/ /_/ /

containerd CLI

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


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.

   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
   oci                        OCI tools
   shim                       interact with a shim directly
   help, h                    Shows a list of commands or help for one command

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

"docker run", "ctr run" コマンドオプションからの機能比較

docker run

$ docker run --help

Usage:  docker run [OPTIONS] IMAGE [COMMAND] [ARG...]

Run a command in a new container

      --add-host list                  Add a custom host-to-IP mapping (host:ip)
  -a, --attach list                    Attach to STDIN, STDOUT or STDERR
      --blkio-weight uint16            Block IO (relative weight), between 10 and 1000, or 0 to disable (default 0)
      --blkio-weight-device list       Block IO weight (relative device weight) (default [])
      --cap-add list                   Add Linux capabilities
      --cap-drop list                  Drop Linux capabilities
      --cgroup-parent string           Optional parent cgroup for the container
      --cgroupns string                Cgroup namespace to use (host|private)
                                       'host':    Run the container in the Docker host's cgroup namespace
                                       'private': Run the container in its own private cgroup namespace
                                       '':        Use the cgroup namespace as configured by the
                                                  default-cgroupns-mode option on the daemon (default)
      --cidfile string                 Write the container ID to the file
      --cpu-period int                 Limit CPU CFS (Completely Fair Scheduler) period
      --cpu-quota int                  Limit CPU CFS (Completely Fair Scheduler) quota
      --cpu-rt-period int              Limit CPU real-time period in microseconds
      --cpu-rt-runtime int             Limit CPU real-time runtime in microseconds
  -c, --cpu-shares int                 CPU shares (relative weight)
      --cpus decimal                   Number of CPUs
      --cpuset-cpus string             CPUs in which to allow execution (0-3, 0,1)
      --cpuset-mems string             MEMs in which to allow execution (0-3, 0,1)
  -d, --detach                         Run container in background and print container ID
      --detach-keys string             Override the key sequence for detaching a container
      --device list                    Add a host device to the container
      --device-cgroup-rule list        Add a rule to the cgroup allowed devices list
      --device-read-bps list           Limit read rate (bytes per second) from a device (default [])
      --device-read-iops list          Limit read rate (IO per second) from a device (default [])
      --device-write-bps list          Limit write rate (bytes per second) to a device (default [])
      --device-write-iops list         Limit write rate (IO per second) to a device (default [])
      --disable-content-trust          Skip image verification (default true)
      --dns list                       Set custom DNS servers
      --dns-option list                Set DNS options
      --dns-search list                Set custom DNS search domains
      --domainname string              Container NIS domain name
      --entrypoint string              Overwrite the default ENTRYPOINT of the image
  -e, --env list                       Set environment variables
      --env-file list                  Read in a file of environment variables
      --expose list                    Expose a port or a range of ports
      --gpus gpu-request               GPU devices to add to the container ('all' to pass all GPUs)
      --group-add list                 Add additional groups to join
      --health-cmd string              Command to run to check health
      --health-interval duration       Time between running the check (ms|s|m|h) (default 0s)
      --health-retries int             Consecutive failures needed to report unhealthy
      --health-start-period duration   Start period for the container to initialize before starting health-retries
                                       countdown (ms|s|m|h) (default 0s)
      --health-timeout duration        Maximum time to allow one check to run (ms|s|m|h) (default 0s)
      --help                           Print usage
  -h, --hostname string                Container host name
      --init                           Run an init inside the container that forwards signals and reaps processes
  -i, --interactive                    Keep STDIN open even if not attached
      --ip string                      IPv4 address (e.g.,
      --ip6 string                     IPv6 address (e.g., 2001:db8::33)
      --ipc string                     IPC mode to use
      --isolation string               Container isolation technology
      --kernel-memory bytes            Kernel memory limit
  -l, --label list                     Set meta data on a container
      --label-file list                Read in a line delimited file of labels
      --link list                      Add link to another container
      --link-local-ip list             Container IPv4/IPv6 link-local addresses
      --log-driver string              Logging driver for the container
      --log-opt list                   Log driver options
      --mac-address string             Container MAC address (e.g., 92:d0:c6:0a:29:33)
  -m, --memory bytes                   Memory limit
      --memory-reservation bytes       Memory soft limit
      --memory-swap bytes              Swap limit equal to memory plus swap: '-1' to enable unlimited swap
      --memory-swappiness int          Tune container memory swappiness (0 to 100) (default -1)
      --mount mount                    Attach a filesystem mount to the container
      --name string                    Assign a name to the container
      --network network                Connect a container to a network
      --network-alias list             Add network-scoped alias for the container
      --no-healthcheck                 Disable any container-specified HEALTHCHECK
      --oom-kill-disable               Disable OOM Killer
      --oom-score-adj int              Tune host's OOM preferences (-1000 to 1000)
      --pid string                     PID namespace to use
      --pids-limit int                 Tune container pids limit (set -1 for unlimited)
      --platform string                Set platform if server is multi-platform capable
      --privileged                     Give extended privileges to this container
  -p, --publish list                   Publish a container's port(s) to the host
  -P, --publish-all                    Publish all exposed ports to random ports
      --pull string                    Pull image before running ("always"|"missing"|"never") (default "missing")
      --read-only                      Mount the container's root filesystem as read only
      --restart string                 Restart policy to apply when a container exits (default "no")
      --rm                             Automatically remove the container when it exits
      --runtime string                 Runtime to use for this container
      --security-opt list              Security Options
      --shm-size bytes                 Size of /dev/shm
      --sig-proxy                      Proxy received signals to the process (default true)
      --stop-signal string             Signal to stop a container (default "SIGTERM")
      --stop-timeout int               Timeout (in seconds) to stop a container
      --storage-opt list               Storage driver options for the container
      --sysctl map                     Sysctl options (default map[])
      --tmpfs list                     Mount a tmpfs directory
  -t, --tty                            Allocate a pseudo-TTY
      --ulimit ulimit                  Ulimit options (default [])
  -u, --user string                    Username or UID (format: <name|uid>[:<group|gid>])
      --userns string                  User namespace to use
      --uts string                     UTS namespace to use
  -v, --volume list                    Bind mount a volume
      --volume-driver string           Optional volume driver for the container
      --volumes-from list              Mount volumes from the specified container(s)
  -w, --workdir string                 Working directory inside the container

ctr run

$ ctr run --help
   ctr run - run a container

   ctr run [command options] [flags] Image|RootFS ID [COMMAND] [ARG...]

   --rm                                    remove the container after running
   --null-io                               send all IO to /dev/null
   --log-uri value                         log uri
   --detach, -d                            detach from the task after it has started execution
   --fifo-dir value                        directory used for storing IO FIFOs
   --cgroup value                          cgroup path (To disable use of cgroup, set to "" explicitly)
   --platform value                        run image for specific platform
   --cni                                   enable cni networking for the container
   --runc-binary value                     specify runc-compatible binary
   --runc-root value                       specify runc-compatible root
   --runc-systemd-cgroup                   start runc with systemd cgroup manager
   --uidmap container-uid:host-uid:length  run inside a user namespace with the specified UID mapping range; specified with the format container-uid:host-uid:length
   --gidmap container-gid:host-gid:length  run inside a user namespace with the specified GID mapping range; specified with the format container-gid:host-gid:length
   --remap-labels                          provide the user namespace ID remapping to the snapshotter via label options; requires snapshotter support
   --cpus value                            set the CFS cpu quota (default: 0)
   --cpu-shares value                      set the cpu shares (default: 1024)
   --snapshotter value                     snapshotter name. Empty value stands for the default value. [$CONTAINERD_SNAPSHOTTER]
   --snapshotter-label value               labels added to the new snapshot for this container.
   --config value, -c value                path to the runtime-specific spec config file
   --cwd value                             specify the working directory of the process
   --env value                             specify additional container environment variables (e.g. FOO=bar)
   --env-file value                        specify additional container environment variables in a file(e.g. FOO=bar, one per line)
   --label value                           specify additional labels (e.g. foo=bar)
   --mount value                           specify additional container mount (e.g. type=bind,src=/tmp,dst=/host,options=rbind:ro)
   --net-host                              enable host networking for the container
   --privileged                            run privileged container
   --read-only                             set the containers filesystem as readonly
   --runtime value                         runtime name (default: "io.containerd.runc.v2")
   --runtime-config-path value             optional runtime config path
   --tty, -t                               allocate a TTY for the container
   --with-ns value                         specify existing Linux namespaces to join at container runtime (format '<nstype>:<path>')
   --pid-file value                        file path to write the task's pid
   --gpus value                            add gpus to the container
   --allow-new-privs                       turn off OCI spec's NoNewPrivileges feature flag
   --memory-limit value                    memory limit (in bytes) for the container (default: 0)
   --device value                          file path to a device to add to the container; or a path to a directory tree of devices to add to the container
   --cap-add value                         add Linux capabilities (Set capabilities with 'CAP_' prefix)
   --cap-drop value                        drop Linux capabilities (Set capabilities with 'CAP_' prefix)
   --seccomp                               enable the default seccomp profile
   --seccomp-profile value                 file path to custom seccomp profile. seccomp must be set to true, before using seccomp-profile
   --apparmor-default-profile value        enable AppArmor with the default profile with the specified name, e.g. "cri-containerd.apparmor.d"
   --apparmor-profile value                enable AppArmor with an existing custom profile
   --rdt-class value                       name of the RDT class to associate the container with. Specifies a Class of Service (CLOS) for cache and memory bandwidth management.
   --rootfs                                use custom rootfs that is not managed by containerd snapshotter
   --no-pivot                              disable use of pivot-root (linux only)
   --cpu-quota value                       Limit CPU CFS quota (default: -1)
   --cpu-period value                      Limit CPU CFS period (default: 0)
   --rootfs-propagation value              set the propagation of the container rootfs