Как пробросить контейнер с mysql к контейнеру с веб сервером?

db:
  image: mysql:5.7
  ports:
    - "3306:3306"
  environment:
    - MYSQL_ROOT_PASSWORD=nimda2017
    - MYSQL_USER=october
    - MYSQL_PASSWORD=secret
    - MYSQL_DATABASE=myAppDB
web:
  image: igontarev/php-server
  ports:
    - "80:80"
    - "443:443"
  links:
    - db
  volumes:
    - ./www:/var/www
    - ./sites:/etc/nginx/sites-enabled
    - ./logs/nginx:/var/log/nginx
    - ./logs/php:/var/log/php
    - ./cron:/etc/cron.d
    - ./supervisor:/etc/supervisor/conf.d
    - ./letsencrypt:/etc/letsencrypt
    - ./lib/letsencrypt:/var/lib/letsencrypt