version: '2'
services:
  myweb:
    extends:
      file: common.yml
      service: web
    command: top
    links:
      - "mydb:db"
    environment:
      # leave FOO alone
      # override BAR
      BAR: "2"
      # add BAZ
      BAZ: "2"
#    net: bridge
  mydb:
    image: busybox
    command: top