Sample docker-compose for Ruby on Rails application

docker-compose.yml

version: '2'
services:
  db:
    image: postgres
    volumes:
      - postgres-volume:/var/lib/postgresql/data
  web:
    build: .
    command: rails s -b 0.0.0.0 -p 3000
    volumes:
      - .:/app
    ports:
      - "3000:3000"
    depends_on:
      - db
    env_file:
      - .env
    environment:
      - DB_USERNAME=postgres
      - DB_PASSWORD=
      - DB_HOST=db
      - DB_NAME=application
volumes:
  postgres-volume: