Docker architecture

Learn the architecture of daemon, CLI and registry.

Docker architecture

Docker has a client-server structure:

Docker CLI (the docker command): takes the commands you type.
Docker daemon (dockerd): runs in the background; manages images, containers, networks and volumes.
Registry: the store where images are kept (Docker Hub, GitHub Container Registry...).

docker pull redis   # CLI -> daemon -> download from the registry
docker run redis    # CLI -> daemon -> create a container

A remote daemon

The CLI and the daemon don't have to be on the same machine. The CLI talks to a REST API over a socket or the network; with the DOCKER_HOST variable or docker context you can manage a daemon on another machine:

docker context create sunucu --docker host=ssh://ali@10.0.0.5
docker context use sunucu
docker ps        # now lists the containers on the remote server

Exercise Pull and run

Write two commands that first pull the redis image, then start a container named cache from it in the background.

Show example solution

docker pull redis
docker run -d --name cache redis

Test yourself

Which component actually creates and manages containers?
- Docker Hub
- The Dockerfile
- The Docker daemon (dockerd)
- The Docker CLI
Show answer

The Docker daemon (dockerd) — The CLI only sends requests to the daemon over a REST API.
Download an image from the registry.
```
docker ____ redis
```
Show answer
```
docker pull redis
```
Match the components with their jobs.

Docker CLI

Sends commands
dockerd

Manages containers
registry

Stores images
docker context

Which daemon to connect to

Next lesson: Use cases

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