docker-compose.yml structuring example

docker-compose.yml

version: "3.4"

# Prepare files for this example:
#   mkdir -p ./a ./b ./c && touch a/a.txt b/b.txt c/c.txt

x-default-image: &x-default-image
  image: ubuntu

x-default-cmd: &x-default-cmd
  command: bash -c "echo $${HELLO} $${SVC_NAME} ; ls -al /tmp/*"

# map merge example
x-default-environment: &x-default-environment
  HELLO: Hi! I am
  SVC_NAME: service-X-DEFAULT

# sequence merge example, there are no "- " prefixes
x-default-volumes: &x-default-volumes |-
  ./a:/tmp/A
  ./b:/tmp/B

services:

  service-A:
    <<:
      - *x-default-image
      - *x-default-cmd
    profiles:
      - a
      - both
    environment:
      # map merge example
      <<: *x-default-environment
      SVC_NAME: service-A
    volumes:
      # sequence merge example
      - *x-default-volumes

  service-B:
    <<: [*x-default-image, *x-default-cmd]
    profiles:
      - b
      - both
    environment:
      <<: *x-default-environment
      SVC_NAME: service-B
    volumes:
      # sequence merge example
      - *x-default-volumes

    depends_on:
      service-A:
        condition: service_completed_successfully
    links:
      - service-A

  service-C:
    <<: [*x-default-image, *x-default-cmd]
    profiles:
      - a
      - c
    environment:
      <<: *x-default-environment
      SVC_NAME: service-C
    volumes:
      # sequence merge example
      - *x-default-volumes
      - ./c:/tmp/C