What does docker-ce-cli & containerd.io installation packages install?

Question

To install docker engine on ubuntu, we run:

  sudo apt-get install docker-ce

But the documentation mentions installation instruction as:

sudo apt-get install docker-ce docker-ce-cli containerd.io

---

$ docker version
Client: Docker Engine - Community
 Version:           19.03.13
 API version:       1.40
 Go version:        go1.13.15
 Git commit:        4484c46d9d
 Built:             Wed Sep 16 17:02:36 2020
 OS/Arch:           linux/amd64
 Experimental:      false

Server: Docker Engine - Community
 Engine:
  Version:          19.03.13
  API version:      1.40 (minimum version 1.12)
  Go version:       go1.13.15
  Git commit:       4484c46d9d
  Built:            Wed Sep 16 17:01:06 2020
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.3.7
  GitCommit:        8fba4e9a7d01810a393d5d25a3621dc101981175
 runc:
  Version:          1.0.0-rc10
  GitCommit:        dc9208a3303feef5b3839f4323d9beb36df0a9dd
 docker-init:
  Version:          0.18.0
  GitCommit:        fec3683
$ 
$ 
$ ps -eaf | grep contain
root      1704     1  0 10:05 ?        00:00:02 /usr/bin/containerd
root      2233     1  0 10:05 ?        00:00:04 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
$ 
$ 

---

Is docker-ce an installation package for docker daemon/server/engine(only)?

Is docker-ce-cli an installation package to install docker client(only)?

Is containerd.io an installation package to install containerd component in below architecture?

Answer 1

Is docker-ce an installation package for docker daemon/server/engine(only)?

Is docker-ce-cli an installation package to install docker client(only)?

Is containerd.io an installation package to install containerd component in below architecture?

Yes to all of those. The architecture diagram is pretty clear. Docker itself used to implement all of this into a single binary, but overtime they decided to embrace the Open Container Initiative (OCI).

containerd is one implementation that follows the OCI. It uses kernel features to provide a runtime environment for containers.

dockerd talks to containerd and also provides more features to Docker users in the form of the easy commands like docker build, docker network, docker volume and docker inspect.

docker-cli provides the docker binary client that talks to the dockerd API, on a local socket or remotely. Even without this client, you could still build and run containers by just using the API.