default docker-compose with alpine-postgresql

docker-compose.yml

db:
  image: kiasaki/alpine-postgres
  ports:
    - "5432"
web:
  build: .
  command: bundle exec rails s -p 9000 -b '0.0.0.0'
  environment:
    BUNDLE_JOBS: 2
    PORT: 9000
  links:
    - db:db
  ports:
    - "9000:9000"
  volumes:
    - ./:/usr/src/app
    - ./vendor/bundle:/bundle