YAML Anchors in Docker Compose

Sometimes, you want to have a Docker Compose file with many services, and you can say that most of the services have configurations that are relatively similar to each other.

Well, under normal circumstances, you might want to have a Docker Compose file for your services like this:

services:
  service-one:
    image: service-one:latest
    networks:
      - custom-network
    environment:
      - one=1
    logging:
      driver: json-file
    deploy:
      replicas: 2
    restart: always
    dns:
      - 8.8.8.8

  service-two:
    image: service-two:latest
    networks:
      - custom-network
    environment:
      - one=1
    logging:
      driver: json-file
    deploy:
      replicas: 2
    restart: always
    dns:
      - 8.8.8.8

networks:
  custom-network:
    driver: bridge

I should mention that there’s an easier way to handle this :)

That is, using YAML Anchors in Docker Compose. YAML Anchors allow you to reuse a section of data in multiple places in the YAML file. By using the “&” and “*” symbols, you can define data once and avoid repetition.

For example, we could have a Docker Compose file like this:

x-service-common: &service-common
  networks:
    - custom-network
  environment:
    - one=1
  logging:
    driver: json-file
  deploy:
    replicas: 2
  restart: always
  dns:
    - 8.8.8.8

services:
  service-one:
    image: service-one:latest
    <<: *service-common

  service-two:
    image: service-two:latest
    <<: *service-common

networks:
  custom-network:
    driver: bridge

In YAML:

• “&” is used to define an anchor (reference).
• “*” is used to refer to that anchor and use its data.

Thank you for your time:)