php – Docker mysql无法连接到容器

我有用于创建mysql映像的docker-compose文件并将端口暴露给3306,但是当我尝试安装CMS时,它给出了错误,它无法连接到数据库.我尝试扫描端口3306,它显示它是打开的,所以MysqL正在运行.

为什么两个docker容器看不到对方？

这是我的docker-compose文件：

PHPfpm:
  restart: always
  extends:
    file: PHP-fpm-5.6.yml
    service: PHPfpm
  links:
    - db:db

Nginx:
  restart: always
  image: Nginx
  ports:
    - "8000:80"
  links:
    - PHPfpm:PHPfpm
  volumes:
    - ./Nginx/vhost.conf:/etc/Nginx/conf.d/default.conf
    - ./app:/var/www/html
    - ./log/Nginx:/var/log/Nginx

db:
  restart: always
  image: MysqL
  ports:
    - "3306:3306"
  environment:
    MysqL_ROOT_PASSWORD: 123456
    MysqL_USER: user
    MysqL_PASSWORD: password
    MysqL_DATABASE: database