Docker Cheat Sheet

Glossary

• Layer
• Image
• Container
• Registry
• Docker Engine / Daemon
• Docker Compose

Useful commands for creating and running containers

Download an image

docker pull image_name

Start and Stop a container

docker [start|stop] container_id|container_name

Create and start a continuer

docker run -it --name container_name image_name command

Create and start a container, and destroy after execution

docker run --rm -it image_name command

Map filesystem, port and environment variables

• Container 80 🠦 Host 8080
• Host /home/user/container_data 🠦 Container /data
• Variable: HTTP_PROXY 🠦 http://proxy.tld:port/

docker run -it --rm -p 80:8080 -v /home/user/container_data:/data -e HTTP_PROXY="http://proxy.tld:port/" image_name command

Create and start a container as daemon (service)

docker -d --name container_name image_name command

Useful commands for cleaning up

Force stop (kill) a container

docker kill container_id|container_name

KIll all running containers

docker kill $(docker ps -q)

Remove stopped a container

docker rm container_id|container_name

Force remove a running container

docker rm --force container_id|container_name

Remover all stopped containers

docker rm $(docker ps -q)

Interact with containers

Run a command inside a running container

docker exec -it container_id|container_name command

Show logs from a running container

docker logs -ft container_id|container_name 

docker attach

Create an image from container

docker commit  -m "commit message" -a "author" container_id|container_name username/image_name:tag

Docker File

Dockerfile

Example of a dockerfile to run busybox

FROM scratch
ADD busybox.tar.xz /
CMD ["sh"]

Explanation

• FROM scratch: use scratch as base image.
• ADD busybox.tar.xz /: Copy busybox from working directory (same as Dockerfile) and extract it to /.
• CMD ["sh"]: tell docker start sh.

Build container

docker build .

Replace . with the path to Dockerfile, to use a Dockerfile in another directory.

Docker Compose

Example of a docker-compose.yml to run a Wordpress blog.

version: '3.3'

services:
   db:
     image: mysql:5.7
     volumes:
       - db_data:/var/lib/mysql
     restart: always
     environment:
       MYSQL_ROOT_PASSWORD: somewordpress
       MYSQL_DATABASE: wordpress
       MYSQL_USER: wordpress
       MYSQL_PASSWORD: wordpress

   wordpress:
     depends_on:
       - db
     image: wordpress:latest
     ports:
       - "8000:80"
     restart: always
     environment:
       WORDPRESS_DB_HOST: db:3306
       WORDPRESS_DB_USER: wordpress
       WORDPRESS_DB_PASSWORD: wordpress
volumes:
    db_data:

Explanation

• version: specify which version of docker-compose to use.
• services: list of images to use
  • image: specify which image to use
  • depends_on: tell docker other image dependencies
  • volumes: refer persistent data storage defined below
  • ports: what ports to expose, otherwise you will not be able to access the application
  • restart: always: tells docker to restart image, each restart
  • environment: define environment variables
• volumes: list of persistent data storage