[ notes to myself ]

Use YAML features in Docker Compose

1 min read

Docker Compose supports features built in to the YAML spec like &anchors and *aliases and << merges, which can be particularly useful with compose fragments and extensions.

Use these features to avoid repeating yourself.

name: example
 
x-defaults: &defaults # extension which defines an anchor fragment
  pull_policy: always
  restart: unless-stopped
  dns: 8.8.8.8
  dns_search: example.com
  env_file: .env
  extra_hosts:
  - "somehost=192.0.2.1"
  - "docker.host.internal=172.17.0.1"
  environment:
    VARIABLE1: "${STR_ONE}"
    VARIABLE2: "${STR_TWO}"
  networks:
  - my-network
 
services:
  web:
    image: nginx:latest
    ports:
    - "8081:80"
    <<: *defaults # YAML merge using an alias to reference the default anchor
  db:
    image: postgres:13
    <<: *defaults
    environment: # this is merged with the environment defined in *defaults
      POSTGRES_USER: example
      POSTGRES_DB: exampledb
      POSTGRES_PASSWORD: "${DB_PASSWORD}"
 
networks:
  my-network:

Backlinks