Docker-compose cheat sheet

NOTES.md

docker-compose cheat sheet

Reference: https://docs.docker.com/compose/compose-file/#compose-file-structure-and-examples

Collection of a few docker-compose examples which I use regularly

Instructions on using docker-compose files

# docker-compsoe version to be used must be mentioned at the top 
version: '3'
services:
  web:
    build: .
    ports:
     - "5000:5000"
  redis:
    image: "redis:alpine"
    
# Each container runs as a different service 

You can mention the dockerfile name in the build. Mostly build "." works always.

version: '2'
services:
  webapp:
    build:
      context: ./dir
      dockerfile: Dockerfile-alternate
      args:
        buildno: 1 
        
version: '2'
services:
  webapp:
    build: . 

If you specify image as well as build, then Compose names the built image with the webapp and optional tag specified in image

build: ./dir
image: webapp:tag

In this general example, the redis service is constrained to use no more than 50M of memory and 0.50 (50%) of available processing time (CPU), and has 20M of memory and 0.25 CPU time reserved (as always available to it).

version: '3'
services:
  redis:
    image: redis:alpine
    deploy:
      resources:
        limits:
          cpus: '0.50'
          memory: 50M
        reservations:
          cpus: '0.25'
          memory: 20M

Environments

Environment variables can be defined in multiple ways

environment:
  RACK_ENV: development
  SHOW: 'true'
  SESSION_SECRET:

environment:
  - RACK_ENV=development
  - SHOW=true
  - SESSION_SECRET

expose

Expose ports without publishing them to the host machine - they’ll only be accessible to linked services. Only the internal port can be specified.

expose:
 - "3000"
 - "8000"

external_links

Link to containers started outside this docker-compose.yml or even outside of Compose, especially for containers that provide shared or common services. external_links follow semantics similar to links when specifying both the container name and the link alias (CONTAINER:ALIAS).

external_links:
 - redis_1
 - project_db_1:mysql
 - project_db_1:postgresql

restart

no is the default restart policy, and it will not restart a container under any circumstance. When always is specified, the container always restarts. The on-failure policy restarts a container if the exit code indicates an on-failure error.

  - restart: no
  - restart: always
  - restart: on-failure

volumes

volumes:
  # Just specify a path and let the Engine create a volume
  - /var/lib/mysql

  # Specify an absolute path mapping
  - /opt/data:/var/lib/mysql

  # Path on the host, relative to the Compose file
  - ./cache:/tmp/cache

  # User-relative path
  - ~/configs:/etc/configs/:ro

  # Named volume
  - datavolume:/var/lib/mysql

volumes_from:
 - service_name
 - service_name:ro
 - container:container_name
 - container:container_name:rw