PHP / MySQL combo

docker-compose.yml

server:
  mem_limit: 301m
  image: webgriffe/docker-php-apache-base:latest
  links:
    - wordpress_db
  ports: 
    - "80:80"
  volumes:
    - .:/var/www/html
  environment:
    APACHE_DOC_ROOT: /var/www/html
    APACHE_DOC_ROOT_ALIAS: /local
    SSMTP_MAILHUB: smtp.server.com
    SSMTP_AUTH_USER: -------
    SSMTP_AUTH_PASS: ------
    SSMTP_USE_STARTTLS: 'yes'

mariadb-data:
  image: tianon/true
  volumes:
    - /var/lib/mysql

wordpress_db:
  mem_limit: 300m
  image: mariadb
  volumes_from:
    - "mariadb-data"
  environment:
    MYSQL_DATABASE: database
    MYSQL_USER: database
    MYSQL_PASSWORD: password
    MYSQL_ROOT_PASSWORD: password2

Warning: If you do a docker-compose pull, it will delete the data of the database. Instead, use docker-compose pull server or docker-compose pull wordpress_db to only update these images without the data.