Docker

Docker commands

docker
    run $name[:$tag] [$cmd]
    ps [-a] [$name]
    stop $name | $id
    rm $name | $id
    images
    rmi $name
    pull $name
    attach $id
    logs $name

Docker run

docker run -it $name  # interactive + terminal
docker run -d 80:8080 $name  # daemon mode, link ports $host:$container
docker run -v /local/dir:/container/dir $name  # mount local volume
docker run -e MYVAR=foobar $name  # pass env var to container

NB: ports and volumes arguments always follow $host:$container order

Creating an image

cat > Dockerfile << EOF
FROM ubuntu
RUN apt-get update
RUN apt-get install python
RUN pip install flask flask-mysql
COPY . /opt/src
ENTRYPOINT FLASK_APP=/opt/src/app.py flask run
EOF

docker build . -t $myname
docker push $myname
docker history $myname  # to see layers (successful RUNs in Dockerfile)

Docker image is built from layers created from each FROM, RUN and COPY line. The layers are reused for different images.

Other useful commands: ENV, WORKDIR, USER, CMD

Network

By default docker uses bridge mode for containers running on the same host with default network 172.17.xxx.xxx. Other network modes are “none” (no network) and “host” (no network isolation from host).

docker network create --driver bridge --subnet 182.18.0.0/16 my_network

docker inspect $name will show full container info including network.

Dockers uses internal DNS 127.0.0.11 to resolve containers IP and containers names.

Storage

Containers, images, volumes are stored in /var/lib/docker. All image layers are RO. A contaier runs in a special RW container layer which gets destroyed when container is stoped. Data can be persisted in named volumes inside /var/lib/docker/volumes (volume mount) or a directory on a host (bind mount).

docker volume create my_volume
docker run -v my_volume:/var/log my_image

# new explicit format for mounting volumes
docker run --mount type=bind,source=/data/my_image/logs,target=/var/log my_image

Removing images

docker images
docker rmi <image_id1> <image_id2>
docker system prune -a
docker volume ls
docker volume rm <volume_name1> <volume_name2>

Docker compose

It’s possible to run multiple containers and “link” them for networking. But much easier to use docker-compose to manage multi-container app.

docker-compose.yml

version: 2

services:
  frontend:
    build:
      context: ./app
      args:
        DB_HOST: localhost:5005
    links:
      - db
    volumes:
      - logs:/var/logs
    depends_on:
      db:
        condition: service_started

  db:
    image: postgres:9.4
    ports:
      - "5005:5432"
    volumes:
      - /data/app/postgres:/var/lib/postgres

volumes:
  logs:

docker-compose up -d   #--build
docker-compose exec frontend ls -l
docker-compose logs frontend
docker-compose down -v