dockerd vs docker-containerd vs docker-runc vs docker-containerd-ctr vs docker-containerd-shim

Question

This stuff is really getting confused now. Can someone please explain what's going on. Just the straight one liner difference.

• dockerd
• libcontainerd
• containerd
• docker-containerd
• docker-runc
• docker-containerd-ctr
• docker-containerd-shim

thanks

Answer 1

dockerd - The Docker daemon itself. The highest level component in your list and also the only 'Docker' product listed. Provides all the nice UX features of Docker.

(docker-)containerd - Also a daemon, listening on a Unix socket, exposes gRPC endpoints. Handles all the low-level container management tasks, storage, image distribution, network attachment, etc...

(docker-)containerd-ctr - A lightweight CLI to directly communicate with containerd. Think of it as how 'docker' is to 'dockerd'.

(docker-)runc - A lightweight binary for actually running containers. Deals with the low-level interfacing with Linux capabilities like cgroups, namespaces, etc...

(docker-)containerd-shim - After runC actually runs the container, it exits (allowing us to not have any long-running processes responsible for our containers). The shim is the component which sits between containerd and runc to facilitate this.

Answer 2

From the documentation:

runC is built on libcontainer which is the same container library powering a Docker engine installation. Prior to the version 1.11, Docker engine was used to manage volumes, networks, containers, images etc.. Now, the Docker architecture is broken into four components:

Docker engine 
containerd
containerd-shm
runC. 

The binaries are respectively called:

docker
docker-containerd
docker-containerd-shim
docker-runc.

https://medium.com/faun/docker-containerd-standalone-runtimes-heres-what-you-should-know-b834ef155426

Answer 3

High-level picture for further better understanding: (read other good answers before this)

Architecture

Source: https://containerd.io/