Docker Compose: Depends_On with an external container?

Question

I'm trying to add depends_on for an external MySQL container named "mysql" (I don't want to create a new mysql container for this stack; I want to use the existing container).

My code so far looks like:

version: '2'

services:
  wordpress:
    image: wordpress:latest
    hostname: mia
    restart: unless-stopped
    ports:
      - 80
    environment:
      WORDPRESS_DB_HOST: mysql:3306
      WORDPRESS_DB_USER: "mia"
      WORDPRESS_DB_PASSWORD: "12345"
      WORDPRESS_DB_NAME: "mia"
    volumes:
      - /f/Sites/mia:/var/www/html
    depends_on:
      - mysql
    networks:
      - occms
      - ocdb

  mysql:
      name: mysql

networks:
  occms:
    external:
      name: cms
  ocdb:
    external:
      name: db

Anyone know a solution?

Answer 1

The depends_on directive only works with services in the same compose project. They may be in different files if you merge those files into the same project, e.g.

docker-compose -f compose-app.yaml -f compose-db.yaml up

Otherwise, I'd recommend moving the startup dependency out of compose and into your application's entrypoint. The common example of this is wait-for-it.sh which would allow you to have an entrypoint script that does:

#!/bin/sh
# delay for mysql startup using wait-for-it for up to 5 minutes
wait-for-it.sh -h mysql -p 3306 -t 300
# call the original wordpress entrypoint script with any args
exec docker-entrypoint.sh "$@"