docker-compose + external container

Question

I have started a docker container with the following command

docker run --name mysql --restart always -p 3306:3306 -v /var/lib/mysql:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=password -d mysql:5.7.14

and then would like to connect a wordpress site with the following docker-compose.yml file

version: '2'

services:
    wordpress:
        image: wordpress
        external_links:
            - mysql:mysql
        ports:
            - 80:80
    environment:
        WORDPRESS_DB_USER: root
        WORDPRESS_DB_PASSWORD: password
    volumes:
        - /var/www/somesite.com:/var/www/html

But I keep getting the following error

Starting somesitecom_wordpress_1
Attaching to somesitecom_wordpress_1
wordpress_1  | 
wordpress_1  | Warning: mysqli::mysqli(): (HY000/2002): Connection refused in - on line 19
wordpress_1  | 
wordpress_1  | MySQL Connection Error: (2002) Connection refused

It seems like the external_links isn't working.

Any idea what I am doing wrong?

Answer 1

Your link is working, but you're on separate networks inside of Docker. From the docker-compose.yml docs:

Note: If you’re using the version 2 file format, the externally-created containers must be connected to at least one of the same networks as the service which is linking to them.

To solve this, you can create your own network:

docker network create dbnet
docker network connect dbnet mysql

Then configure your docker-compose.yml with:

version: '2'

networks:
  dbnet:
    external:
      name: dbnet

services:
    wordpress:
        image: wordpress
        ports:
            - 80:80
        environment:
            WORDPRESS_DB_USER: root
            WORDPRESS_DB_PASSWORD: password
        volumes:
            - /var/www/somesite.com:/var/www/html
        networks:
          - dbnet

Note with recent versions of Docker, you shouldn't need to link the containers, the DNS service should do the name resolution for you.