Containers and images

What a container is and how to run one.

A container is an isolated process that carries everything it needs: code, runtime and libraries. It starts in seconds and behaves the same on your laptop and on a server. It is not a full virtual machine: containers share the host kernel.

• Image: a read-only template (for example nginx or python:3.12).
• Container: a running instance of an image.
• Registry: where images are stored, such as Docker Hub.

Run your first container

docker run hello-world                       # downloads the image if needed, runs it, exits
docker run -d -p 8080:80 --name web nginx    # run in background, map host port 8080 to container port 80
docker ps                                    # running containers
docker ps -a                                 # including stopped ones
docker logs web                              # output of the container
docker stop web && docker rm web             # stop and remove it

After the nginx command, open http://localhost:8080 to see the web server. -p HOST:CONTAINER maps ports.

Images

docker pull python:3.12      # download an image
docker images                # list local images
docker rmi python:3.12       # remove an image

NoteAlways use a specific tag such as python:3.12 instead of relying on latest, so builds are repeatable.