Docker Go-to guide

This post consists of all the frequently used commands for docker. I am posting it for my reference. Feel free to use it.

Basic Architecture & Terminology

docker client <-> docker daemon/engine/server (lightweight linux VM) -> containers

Container Images:

  • Read only templates used to create containers
  • Created with docker build command
  • Composed of layers of other images
  • Stored in docker registry like docker hub
  • If image is a class, then container is an instance (object) of a class

Containers: lightweight and portable encapsulations of an environment in which to run applications.

Registry: where we store images, like dockerhub


  • Public registry for docker
  • Recommended to use official images only in production

Some Useful Commands

  • Force delete all images with repotags:

    docker rmi -f $(sudo docker images -f "dangling=true" -q)
  • Docker Interactive -i interactive and -t pseudo TTY

  • Detached mode using -d

  • Low level info:

    docker inspect <container_id>
  • Port mapping:

    -p host_port:container_port
    docker run -it -p 8888:8080 tomcat
  • Logs of running container

    docker logs <container_id>
  • Image layers

    • changes made into the running containers are written to the writable layer
    • writable layer is deleted when container is deleted but underlying layer remains.
    • multiple containers can share same underlying image
    docker history busybox
  • Commit changes made in Docker container
    • spin up a container from base image
    docker run -it debian:jessie
    apt install -y git
    docker commit <container_id> <repo_name:tag>
    docker run -it <repo_name:tag>
  • Dockerfile
    • contains instructions users provide to assemble image
    • each instruction creates new image layer over underlying base image.
    FROM debian:jessie
    RUN apt-get update && apt-get install -y \
      git \
    RUN useradd -ms /bin/bash admin
    USER admin
    docker build -t <repo_name:tag> .

NOTE: When build starts, docker client packs all files in the build context into a tarball and transfers it into the daemon.

  • Docker cache
    • if instruction doesn’t change, Docker reuses existing layer instead of building new one each time.
  • Aggressive Caching achieved by chaining apt-get update && apt-get install

  • ADD action downloads file and copies to container, can automatically unpack compressed files.

  • Push images to Docker hub

    docker tag <image_id> <docker_hub_id/debian:tag>
    # Note: avoid using latest tag. Explicitly state a tag every time.
    # Because images which are tagged latest will not be
    # updated automatically when a # newer version of the image is pushed to # the repo.
    docker login --username=<USERNAME>
    docker push <docker_hub_id/debian:tag>
  • Run commands in container

    docker exec -it <container_id> bash
  • Link Docker Containers

    docker build -t app:v0.1
    dockcer run -d -p 8000:8000 --link redis app:v0.1

Docker Compose - Automate docker workflow

Impractical for large number of containers, especially when linking them.


version: '2'
    build: .
      - "8000:8000"
      - <host_dir>:</container_dir> # ./app:/app

    image: redis:3.2.0

Some more commands:

docker-compose up -d
docker-compose ps

# appended logs
docker-compose logs -f <container_name>

# stop
docker-compose stop

# remove containers
docker-compose rm

# force rebuild image
docker-compose build
docker-compose up -d

Docker Container Networking

  • uses bridged network by default
  • closed(none) - no access to outside internet, closed container, max level of network protection.

    docker run -d --net none busybox sleep 1000
  • bridged - default network type, access to outside internet and to other containers on bridge
    • Connect multiple bridges together which however is not possible by default. But docker has an option to enable this:
    docker network create --driver bridge <network_name>
    docker network ls
  • Some more networking related commands

    # find the subnet & gateway
    docker network inspect <network_name>
    # assign a container to the newly created network
    docker run -d --name <container_name> --net <network_name> busybox sleep 1000
    # connect new container to first(old) bridge network
    docker network connect bridge <container_name>
    # disconnect
    docker network disconnect bridge <container_name>
  • host
    • least protected network model
    • adds a container on the host’s network stack
    • usually called open containers
    • only benefit is performance of network
    • never use in production unless there is no other option
  • overlay network
    • multi-host networking, require pre-existing conditions like, running docker in swarm mode

Define container networks with docker-compose.yml

      - <network_name>
      - <network_name>
    driver: bridge

Spin it up using: docker-compose up -d

Exec in docker containers

# first build
docker-composer up -d

# run command inside 'app' container
docker-compose run app php test.php

Docker in production

  • Use COPY instead of volumes mount COPY app /app

  • docker-machine

    docker-machine create --driver digitalocean -- digitalocean-access-token <DO_Token> <VM_Name>
  • Multiple env support

    docker-machine env <vmname>
    cp compose.yml prod.yml
    build -> image
    docker-compose -f prod.yml up -d

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