Docker, multiple MySQL containers on same network - intermittent connection problems

Question

Fairly new to docker, but I have 2 projects - project-a and project-b, I would like to develop on them both locally using docker, with an nginx-proxy container to route between them.

So far I have:

1) Create a new docker network called 'my-network' in bridge mode. 2) Started up nginx-proxy container, and configured dnsmasq to route '.dev' domains to individual containers (this all works fine) 3) Starting up project-a with the following docker-compose.yml file

version: '3.2'

services:
  web:
    image: brettt89/silverstripe-web
    working_dir: /var/www
    restart: unless-stopped
    volumes:
      - .:/var/www/html
    environment:
      - VIRTUAL_HOST=project-a.dev

  db:
    image: mysql
    volumes:
      - db-data:/var/lib/mysql
    restart: unless-stopped
    environment:
      MYSQL_ROOT_PASSWORD: password

volumes:
  db-data:

networks:
  default:
    external:
      name: my-network

This all works as expected with nginx-proxy routing requests for project-a.dev through to this container. MySQL queries work as expected.

However, once I start project-b with the same docker-compose file (except changing the VIRTUAL_HOST env variable to project-b.dev) the problems begin. I can successfully navigate to project-b.dev, however I get intermittent database connection errors across page loads and refreshes - the same errors also start to occur on project-a.dev

Does anyone have any ideas what I'm doing wrong?

Answer 1

As you use the same docker compose, you have 2 database containers, 1 for each project. But they use the same volume. I think it can be a problem. Try to modify the volume name for tour project B (db-data-b for example).

*EDIT for the good answer: * Try not to use the bridged network or inspect containers to avoid IP conflicts.