Painless Docker - 2nd Edition

Managing Service Dependencies

In the previous example, we have two services: db and wordpress. The wordpress service, in reality, depends on the db service. This means that the wordpress service cannot start until the db service is up and running. If we start the wordpress service without starting the db service, we will get an error.

Therefore, we need to start the db service first, then start the wordpress service. In Docker Compose, we can do this using the depends_on option:

services:
   db:
     image: mysql:9.6.0
     volumes:
       - db_data:/var/lib/mysql
     restart: always
     environment:
       MYSQL_ROOT_PASSWORD: mypassword
       MYSQL_DATABASE: wordpress
       MYSQL_USER: user
       MYSQL_PASSWORD: