Multiple docker-compose: Error: getaddrinfo EAI_AGAIN from frontend to backend

Question

I have 2 folders separated, one for backend and one for frontend services:

• backend/docker-compose.yml
• frontend/docker-compose.yml

The backend has a headless wordpress installation on nginx, with the scope to serve the frontend as an api service. The frontend runs on next.js. Here are the 2 different docker-compose.yml:

backend/docker-compose.yml

version: '3.9'

services:
  nginx:
    image: nginx:latest
    container_name: my-app-nginx
    ports:
      - '80:80'
      - '443:443'
      - '8080:8080'
    ...
    networks:
      - internal-network

  mysql:
    ...
    networks:
      - internal-network

  wordpress:
    ...
    networks:
      - internal-network

networks:
  internal-network:
    external: true

frontend/docker-compose.yml

version: '3.9'

services:
  nextjs:
    build:
      ...
    container_name: my-app-nextjs
    restart: always
    ports:
      - 3000:3000
    networks:
      - internal-network
  
networks:
  internal-network:
    driver: bridge
    name: internal-network

In the frontend I use the fetch api in nextjs as following:

fetch('http://my-app-nginx/wp-json/v1/enpoint', ...)

I tried also with ports 80 and 8080, without success.

The sequence of commands I run are:

• docker network create internal-network
• in backend/ folder, docker-compose up -d (all backend containers run fine, I can fetch data with Postman from WordPress api)
• in frontend/ folder, docker-compose up -d fails with the error Error: getaddrinfo EAI_AGAIN my-app-nginx

I am not a very expert user of docker so I might miss something here, but I understand that there might be internal network issues over the containers. I read many answers regarding this topic but I couldn't figure it out.

Any recommendations?

Answer 1

Just to add a proper answer:

• Generally you should NOT really want to be executing multiple docker-compose up -d commands
• If you want to combine two separate docker-compose configs and run as one (slightly more preferable), you can use the extends keyword as described in the docs

However, I would suggest that you treat it as a single docker-compose project which can itself have multiple nested git repositories:

• Example SO answer - Git repository setup for a Docker application consisting of multiple repositories
• You can keep your code in a mono-repo or multiple repos, up to you

Real working example to backup using your applications that validates this approach:

• headless-wordpress-nextjs-starter-kit and it's docker-compose.yml

Answer 2

I have found this thread here Communication between multiple docker-compose projects

By looking at the most upvoted answers, I wonder if it is related to network prefix?

It seems like the internal-network would be prefixed with frontend_? On the other hand you can also try to locate the network by name in backend/docker-compose.yml:

networks:
  internal-network:
    external: 
      name: internal-network

Answer 3

The issue is external networks need the network name specified (because docker compose prefixes resources by default). Your backend docker compose network section should look like this:

networks:
  internal-network:
    name: internal-network
    external: true

You are creating the network in your frontend docker compose so you should omit the docker network create ... command (just need to init frontend first). Or instead treat them both as external and keep the command. In which use the named external network as shown above in your frontend docker compose as well.