docker-compose.yml

version: '2.1'

volumes:
  postgres-data:
    driver: local

services:
  # service configuration for our dockerized Rails app
  app:
  
    # use the Dockerfile next to this file
    build: .
  
    # rely on the RAILS_ENV value of the host machine
    environment:
      - RAILS_ENV=development
  
    # makes the app container aware of the DB container
    links:
      - db
  
    # expose the port we configured Unicorn to bind to
    ports:
        - "3000:3000"
        #

    # map our application source code, in full, to the application root of our container
    volumes:
      - .:/var/www/docker_example
  
  # service configuration for our database
  db:
   
    # use the preferred version of the official Postgres image
    # see https://hub.docker.com/_/postgres/
    image: postgres:9.4.5
  
    # persist the database between containers by storing it in a volume
    volumes:
      - postgres-data:/var/lib/postgresql/data