docker-compose.yml

version: '3.1'

services:
  
  # name of service. Both services will be attached to the default bridge network created at compose
  # time. DNS's on the same network have automatic resolution to their IP. 
  # ch stands for Companies House.
  
  ch_pg:

    image: postgres

    restart: always

    environment:
      POSTGRES_PASSWORD: ch_pass
      POSTGRES_USER: ch_user
      POSTGRES_DB: ch_db

    ports:
      - 5432:5432

    volumes:
      - postgres_data:/var/lib/postgresql/data
 
  ch_app:

    # at build time the deamon looks for Dockerfile in specified context.
    build:
      context: .  # context = folder where the docker-compose.yml is.
        
    # Default entrypoint: python3 /scr_code/app.py /scr_code/file.txt 
   
    entrypoint: 
      - python3 
      - /code/app.py 
      - /code/file.txt

    depends_on: 
      - ch_pg  # will be built before ch_app

    volumes:
      - ch_app_data:/code


# [ volumes definition ]
# creates Docker volumes which can be mounted by other containers too e.g. for backup

volumes:

  postgres_data:
    driver: local
    driver_opts:
      type: none
      o: bind
      device: ${PWD}/postgres_data

  ch_app_data:
    driver: local
    driver_opts:
      type: none
      o: bind
      device: ${PWD}/code