HAProxy: expose containers with subdomains

docker-compose.yml

webclient:
  environment:
    - NODE_ENV=production
    - VIRTUAL_HOST=myapp.com
  build: 'webclient' # this directory must have a Dockerfile
  links:
    - mongo
  restart: always

lb:
  image: 'dockercloud/haproxy'
  links:
    - webclient
    - api
  ports:
    - '80:80'
  restart: always

api:
  environment:
    - NODE_ENV=production
    - VIRTUAL_HOST=api.myapp.com
  build: 'server' # this directory must have a Dockerfile
  links:
    - mongo
  restart: always

mongo:
  image: 'mongo:latest'
  restart: always