无法连接到通过docker-compose创建的MySQL docker容器(Can't connect to MySQL docker container created via docker-compose)

 我想开始使用docker并使用nginx容器，PHP-FPM容器和MySQL容器创建一个简单的容器环境。 
 
 虽然nginx和PHP-FPM容器之间的链接运行良好，但我似乎无法将PHP应用程序服务器与数据库服务器链接。 
 
 我使用docker-compose来最小化手动终端工作。 我的docker-compose.yml看起来像这样： 
 
web:
  image: tutorial/nginx
  ports:
    - "8080:80"
  volumes:
    - ./src:/var/www
    - ./src/vhost.conf:/etc/nginx/sites-enabled/vhost.conf
  links:
    - php
php:
  image: nmcteam/php56
  volumes:
    - ./src/php-fpm.conf:/etc/php5/fpm/php-fpm.conf
    - ./src:/var/www
  links:
    - db
db:
  image: sameersbn/mysql
  volumes:
   - /var/lib/mysql
  environment:
   - DB_NAME=demoDb
   - DB_USER=demoUser
   - DB_PASS=demoPass
 
 我尝试使用以下语句连接到DB： 
 
$db = new \PDO('mysql:host=db;dbname=demoName', 'demoUser', 'demoPass');
 
 MySQL容器本身正在工作，因为我可以连接到容器bash并使用MySQL CLI： 
 
mysql> show databases;

+--------------------+
| Database           |
+--------------------+
| information_schema |
| demoDb             |
| mysql              |
| performance_schema |
+--------------------+
 
 我只是得到一个500错误，并找不到为什么这不起作用的原因。 任何对我可能错过的帮助或建议都不胜感激。 

I want to get started with docker and created a simple container environment with an nginx container, a PHP-FPM container and a MySQL container. 
 
While the link between the nginx and PHP-FPM container works well I can't seem to link the PHP application server with the database server.
 
I use docker-compose to minimize the manual terminal work. My docker-compose.yml looks like this:
 
web:
  image: tutorial/nginx
  ports:
    - "8080:80"
  volumes:
    - ./src:/var/www
    - ./src/vhost.conf:/etc/nginx/sites-enabled/vhost.conf
  links:
    - php
php:
  image: nmcteam/php56
  volumes:
    - ./src/php-fpm.conf:/etc/php5/fpm/php-fpm.conf
    - ./src:/var/www
  links:
    - db
db:
  image: sameersbn/mysql
  volumes:
   - /var/lib/mysql
  environment:
   - DB_NAME=demoDb
   - DB_USER=demoUser
   - DB_PASS=demoPass
 
While I try to connect to the DB with the following statement:
 
$db = new \PDO('mysql:host=db;dbname=demoName', 'demoUser', 'demoPass');
 
The MySQL container itself is working as I can connect to the containers bash and use the MySQL CLI:
 
mysql> show databases;

+--------------------+
| Database           |
+--------------------+
| information_schema |
| demoDb             |
| mysql              |
| performance_schema |
+--------------------+
 
I just get a 500 error and can't find a reason why this wouldn't work. Any help or suggestion of what I might have missed is more than appreciated.

原文：https://stackoverflow.com/questions/37463543