docker-compose.yaml

# we'll call our web app of web
web:
  # it'll build this container based the docker file ./Dockerfile
  build: .
  # it'll run this command to star the server
  command: bash -c "rm -f tmp/pids/server.pid || true && bundle exec rails s -p 3000 -b '0.0.0.0'"
  # it'll export the port 3000
  ports:
    - "3000:3000"
  # it links to db container (on mongoid.yaml at rail's config we say host: db:27017 it's linked)
  links:
    - db
# we called our db container of db :)
db:
  # instead of building it from zero we'll use an existent image (see docker hub)
  image: mongo
  # it needs to persist data so we keep it (even if we "kill" the container)
  volumes:
    - /data/db
  # we export the port 27017 :B 
  ports:
    - "27017:27017"
# we'll use nginx as web server
nginx:
  # it'll restart when the container does too
  restart: always
  # we're going to build this container from docker file ./docker/nginx/Dockerfile
  build: ./docker/nginx/
  # we're gonna expose 80
  ports:
    - "80:80"
  # since we'll be a proxy we need to be linked to our web app (upstream= web:3000)
  links:
    - web:web