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Docker-Compose Cheatsheet

Key features of Docker Compose

Have multiple isolated environments on a single host

Compose uses a project name to isolate environments from each other. You can make use of this project name in several different contexts:

  • on a dev host, to create multiple copies of a single environment, such as when you want to run a stable copy for each feature branch of a project
  • on a CI server, to keep builds from interfering with each other, you can set the project name to a unique build number
  • on a shared host or dev host, to prevent different projects, which may use the same service names, from interfering with each other

The default project name is the basename of the project directory. You can set a custom project name by using the -p command line option or the COMPOSE_PROJECT_NAME environment variable.

The default project directory is the base directory of the Compose file. A custom value for it can be defined with the --project-directory command line option.

Preserves volume data when containers are created

Compose preserves all volumes used by your services. When docker compose up runs, if it finds any containers from previous runs, it copies the volumes from the old container to the new container. This process ensures that any data you've created in volumes isn't lost.

Only recreate containers that have changed

Compose caches the configuration used to create a container. When you restart a service that has not changed, Compose re-uses the existing containers. Re-using containers means that you can make changes to your environment very quickly.

Supports variables and moving a composition between environments

Compose supports variables in the Compose file. You can use these variables to customize your composition for different environments, or different users. You can extend a Compose file using the 'extends` field or by creating multiple Compose files.

Common use cases

Compose can be used in many different ways. Some common use cases are outlined below.

Development environments

When you're developing software, the ability to run an application in an isolated environment and interact with it is crucial. The Compose command line tool can be used to create the environment and interact with it. The Compose file provides a way to document and configure all of the application's service dependencies (databases, queues, caches, web service APIs, etc). Using the Compose command line tool you can create and start one or more containers for each dependency with a single command (docker compose up).

Together, these features provide a convenient way for developers to get started on a project. Compose can reduce a multi-page "developer getting started guide" to a single machine readable Compose file and a few commands.

Automated testing environments

An important part of any Continuous Deployment or Continuous Integration process is the automated test suite. Automated end-to-end testing requires an environment in which to run tests. Compose provides a convenient way to create and destroy isolated testing environments for your test suite. By defining the full environment in a Compose file, you can create and destroy these environments in just a few commands:

docker compose up -d
./run_tests
docker compose down

Commands

docker-compose start
docker-compose stop

docker-compose pause
docker-compose unpause

docker-compose ps
docker-compose up
docker-compose up -d    # Start Detached
docker-compose down
docker-compose down -v    # Remove Unused Volumes

Reference

Building

web:
  # build from Dockerfile
  build: .
  args:     # Add build arguments
    APP_HOME: app

  # build from custom Dockerfile
  build:
    context: ./dir
    dockerfile: Dockerfile.dev

  # build from image
  image: ubuntu
  image: ubuntu:14.04
  image: tutum/influxdb
  image: example-registry:4000/postgresql
  image: a4bc65fd

Ports

  ports:
    - "3000"
    - "8000:80"  # host:container

  # expose ports to linked services (not to host)
  expose: ["3000"]

Commands

  # command to execute
  command: bundle exec thin -p 3000
  command: [bundle, exec, thin, -p, 3000]

  # override the entrypoint
  entrypoint: /app/start.sh
  entrypoint: [php, -d, vendor/bin/phpunit]

Environment variables

  # environment vars
  environment:
    RACK_ENV: development
  environment:
    - RACK_ENV=development

  # environment vars from file
  env_file: .env
  env_file: [.env, .development.env]

Dependencies

  # makes the `db` service available as the hostname `database`
  # (implies depends_on)
  links:
    - db:database
    - redis

  # make sure `db` is alive before starting
  depends_on:
    - db

  # make sure `db` is healty before starting
  # and db-init completed without failure
  depends_on:
    db:
      condition: service_healthy
    db-init:
      condition: service_completed_successfully

Other options

  # make this service extend another
  extends:
    file: common.yml  # optional
    service: webapp

  volumes:
    - /var/lib/mysql
    - ./_data:/var/lib/mysql

  # automatically restart container
  restart: unless-stopped
  # always, on-failure, no (default)

Advanced features

Labels

services:
  web:
    labels:
      com.example.description: "Accounting web app"

DNS servers

services:
  web:
    dns: 8.8.8.8
    dns:
      - 8.8.8.8
      - 8.8.4.4

Devices

services:
  web:
    devices:
    - "/dev/ttyUSB0:/dev/ttyUSB0"

services:
  web:
    external_links:
      - redis_1
      - project_db_1:mysql

Healthcheck

    # declare service healthy when `test` command succeed
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost"]
      interval: 1m30s
      timeout: 10s
      retries: 3
      start_period: 40s

Hosts

services:
  web:
    extra_hosts:
      - "somehost:192.168.1.100"

Network

# creates a custom network called `frontend`
networks:
  frontend:

External network

# join a pre-existing network
networks:
  default:
    external:
      name: frontend

Volume

# mount host paths or named volumes, specified as sub-options to a service
  db:
    image: postgres:latest
    volumes:
      - "/var/run/postgres/postgres.sock:/var/run/postgres/postgres.sock"
      - "dbdata:/var/lib/postgresql/data"

volumes:
  dbdata:

User

# specifying user
user: root

# specifying both user and group with ids
user: 0:0

Example Docker-Compose File

version: '3.3'
services:
    elasticsearch:
        container_name: elasticsearch
        environment:
            - discovery.type=single-node
        ports:
            - '9200:9200'
            - '9300:9300'
        image: 'elasticsearch:latest'
        networks:
            - elastic
networks:
    elastic:
        driver: bridge