Docker
Referenced from here.
Referenced from here.
Referenced from here.
Components
- dockerd
- containerd
- containerd-shim
- runc
runc
CLI tool for spawning and running containers according to the OCI specification.
containerd-shim
The shim allows for daemonless containers. It basically sits as the parent of the container’s process to facilitate a few things.
- First it allows the runtimes(i.e.
runc) to exit after it starts the container. This way we don’t have to have the long running runtime processes
for containers. When you start mysql you should only see the mysql process and the shim. - Second it keeps the STDIO and other fds open for the container incase
containerd and/or docker both die. If the shim was not running then the
parent side of the pipes or the TTY master would be closed and the container would exit. - Finally it allows the container’s exit status to be reported back to a higher level tool like docker without having the be the actual parent of the
container’s process and do a
wait4.
containerd
containerd was introduced in Docker 1.11 and since then took main responsibility of managing containers life-cycle. containerd is the executor
for containers, but has a wider scope than just executing containers. So it also take care of:
- Image push and pull
- Managing of storage
- Of course executing of Containers by calling runc with the right parameters to run containers…
- Managing of network primitives for interfaces
- Management of network namespaces containers to join existing namespaces
dockerd
The Docker daemon - dockerd listens for Docker API requests and manages host’s Container life-cycles by utilizing containerd.
dockerd can listen for Docker Engine API requests via three different types of Socket: unix, tcp, and fd.
By default, a unix domain socket is created at /var/run/docker.sock, requiring either root permission, or docker group membership.
On Systemd based systems, you can communicate with the daemon via Systemd socket activation,
use dockerd -H fd://.
Workflow among the above components
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| ❯ docker --version
Docker version 20.10.5, build 55c4c88
❯ sudo docker container ls
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
05ebb62bc655 nginx "/docker-entrypoint.…" 13 days ago Up 13 days 80/tcp nginx2
7f3fa77ddad8 nginx "/docker-entrypoint.…" 13 days ago Up 13 days 80/tcp nginx1
❯ ps -ef --forest | grep -v " --color=auto" | grep -A3 -E "dockerd|containerd"
root 714 1 0 Mar17 ? 00:17:12 /usr/bin/containerd
root 1931 1 0 Mar17 ? 00:02:53 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
root 2139 1 0 Mar17 ? 00:01:04 /usr/bin/containerd-shim-runc-v2 -namespace moby -id 7f3fa77ddad85e82619b21d6fd9bde8c6fa7cce9e1c063b4f18f258c1206b1e4 -address /run/containerd/containerd.sock
root 2163 2139 0 Mar17 ? 00:00:00 \_ nginx: master process nginx -g daemon off;
systemd+ 2217 2163 0 Mar17 ? 00:00:00 \_ nginx: worker process
root 2240 1 0 Mar17 ? 00:01:05 /usr/bin/containerd-shim-runc-v2 -namespace moby -id 05ebb62bc6557c76f9d4494bbd2262e9fa7f91c3a0bad14677455a158e949f75 -address /run/containerd/containerd.sock
root 2261 2240 0 Mar17 ? 00:00:00 \_ nginx: master process nginx -g daemon off;
systemd+ 2319 2261 0 Mar17 ? 00:00:00 \_ nginx: worker process
=================================
❯ docker --version
Docker version 19.03.15, build 99e3ed8919
❯ docker container ls
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
cbb233ea0045 nginx "/docker-entrypoint.…" 11 minutes ago Up 11 minutes 80/tcp nginx2
fa3468d6e89a nginx "/docker-entrypoint.…" 11 minutes ago Up 11 minutes 80/tcp nginx1
❯ ps -ef --forest | less
root 184283 1 0 14:10 ? 00:00:00 /usr/bin/containerd
root 184493 184283 0 14:11 ? 00:00:00 \_ containerd-shim -namespace moby -workdir /var/lib/containerd/io.containerd.runtime.v1.linux/moby/fa3468d6e89a7ddcbd67a7049b2fd1771555c445ba6e8795a4634cb4795ecdd6 -address /run/containerd/containerd.sock -containerd-binary /usr/bin/containerd -runtime-root /var/run/docker/runtime-runc
root 184509 184493 0 14:11 ? 00:00:00 | \_ nginx: master process nginx -g daemon off;
101 184564 184509 0 14:11 ? 00:00:00 | \_ nginx: worker process
root 184595 184283 0 14:11 ? 00:00:00 \_ containerd-shim -namespace moby -workdir /var/lib/containerd/io.containerd.runtime.v1.linux/moby/cbb233ea004589877970ee3b4bcd08672370c159720617c29c31b943e4a5be3c -address /run/containerd/containerd.sock -containerd-binary /usr/bin/containerd -runtime-root /var/run/docker/runtime-runc
root 184611 184595 0 14:11 ? 00:00:00 \_ nginx: master process nginx -g daemon off;
101 184663 184611 0 14:11 ? 00:00:00 \_ nginx: worker process
root 184291 1 0 14:10 ? 00:00:01 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
=================================
❯ podman version
Version: 2.2.1
API Version: 2
Go Version: go1.14.12
Built: Mon Feb 22 12:51:35 2021
OS/Arch: linux/amd64
❯ podman container ls
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
2fed78dd707e docker.io/library/nginx:latest nginx -g daemon o... 2 minutes ago Up 2 minutes ago nginx2
75103237f3d5 docker.io/library/nginx:latest nginx -g daemon o... 2 minutes ago Up 2 minutes ago nginx1
❯ runc list
ID PID STATUS BUNDLE CREATED OWNER
2fed78dd707e865d4995f2d80dd9ee7830776e8adfe62f2b5b2754fa8b950be9 188922 running /var/lib/containers/storage/overlay-containers/2fed78dd707e865d4995f2d80dd9ee7830776e8adfe62f2b5b2754fa8b950be9/userdata 2021-03-31T06:36:31.164181537Z root
75103237f3d5f8d78f1d34cd32747c083f8d59eb5df4d09e3e68ab8279fcf832 188806 running /var/lib/containers/storage/overlay-containers/75103237f3d5f8d78f1d34cd32747c083f8d59eb5df4d09e3e68ab8279fcf832/userdata 2021-03-31T06:36:25.812499602Z root
❯ runc state 2fed78dd707e865d4995f2d80dd9ee7830776e8adfe62f2b5b2754fa8b950be9
{
"ociVersion": "1.0.2-dev",
"id": "2fed78dd707e865d4995f2d80dd9ee7830776e8adfe62f2b5b2754fa8b950be9",
"pid": 188922,
"status": "running",
"bundle": "/var/lib/containers/storage/overlay-containers/2fed78dd707e865d4995f2d80dd9ee7830776e8adfe62f2b5b2754fa8b950be9/userdata",
"rootfs": "/var/lib/containers/storage/overlay/9fde6f2ab9dee9701adce3862803afe893c009269e74c0c77e18c4454c9184d1/merged",
"created": "2021-03-31T06:36:31.164181537Z",
"annotations": {
"io.container.manager": "libpod",
"io.kubernetes.cri-o.Created": "2021-03-31T14:36:30.807867268+08:00",
"io.kubernetes.cri-o.TTY": "false",
"io.podman.annotations.autoremove": "FALSE",
"io.podman.annotations.init": "FALSE",
"io.podman.annotations.privileged": "FALSE",
"io.podman.annotations.publish-all": "FALSE",
"org.opencontainers.image.stopSignal": "3"
},
"owner": ""
}#
❯ ps -ef --forest
root 188797 1 0 14:36 ? 00:00:00 /usr/bin/conmon --api-version 1 -c 75103237f3d5f8d78f1d34cd32747c083f8d59eb5df4d09e3e68ab8279fcf832 -u 75103237f3d5f8d78f1d34cd32747c083f8d59eb5df4d09e3e68ab8279fcf832 -r /usr/bin/runc -b /var/lib/containers/storage/overlay-containers/75103237f3d5f8d78f1d34cd32747c08/run/containers/storage/overlay-containers/75103237f3d5f8d78f1d34cd32747c083f8d59eb5df4d09e3e68ab8279fcf832/userdata/conmon.pid --exit-command /usr/bin/podman --exit-command-arg --root --exit-command-arg /var/lib/containers/storage --exit-command-arg --runroot --exit-command-arg /var/run/containers/storage --exit-comm
root 188806 188797 0 14:36 ? 00:00:00 \_ nginx: master process nginx -g daemon off;
101 188842 188806 0 14:36 ? 00:00:00 \_ nginx: worker process
root 188913 1 0 14:36 ? 00:00:00 /usr/bin/conmon --api-version 1 -c 2fed78dd707e865d4995f2d80dd9ee7830776e8adfe62f2b5b2754fa8b950be9 -u 2fed78dd707e865d4995f2d80dd9ee7830776e8adfe62f2b5b2754fa8b950be9 -r /usr/bin/runc -b /var/lib/containers/storage/overlay-containers/2fed78dd707e865d4995f2d80dd9ee78/run/containers/storage/overlay-containers/2fed78dd707e865d4995f2d80dd9ee7830776e8adfe62f2b5b2754fa8b950be9/userdata/conmon.pid --exit-command /usr/bin/podman --exit-command-arg --root --exit-command-arg /var/lib/containers/storage --exit-command-arg --runroot --exit-command-arg /var/run/containers/storage --exit-comm
root 188922 188913 0 14:36 ? 00:00:00 \_ nginx: master process nginx -g daemon off;
101 188955 188922 0 14:36 ? 00:00:00 \_ nginx: worker process
|