Docker compose can't resolve hostname in local network

[loic-h]

To Reproduce

Here is a docker compose app which only try to connect to a mongo database:

services:
  mongosh:
    image: alpine/mongosh:latest
    command: sh -c "mongosh 'mongodb://mongo' && tail -f /dev/null"
    depends_on:
      - mongo

  mongo:
    image: mongo:latest
    ports:
      - '27018:27017'
    command:
      - --storageEngine=wiredTiger
    volumes:
      - data:/data/db
    logging:
      driver: none

volumes:
  data:
  node_modules:

Current vs. Expected behavior

Current behavour The mongosh app can't connect to the mongo database.

Connecting to: mongodb://mongo/?directConnection=true&appName=mongosh+2.0.2
MongoServerSelectionError: getaddrinfo EAI_AGAIN mongo

I tried pinging the mongo hostname in the docker container and it couldn't resolve it:

> docker exec -it test-mongonet-qbhbhx-node-1 ping mongo
ping: bad address 'mongo'

Expected behaviour The mongosh app should connect to the mongo database.

Provide environment information

Operating system: Ubuntu 25.04
Dokploy version: 0.25.11
Services deployed: mongo and mongosh apps via docker compsoe

Which area(s) are affected? (Select all that apply)

Docker Compose

Are you deploying the applications where Dokploy is installed or on a remote server?

Same server where Dokploy is installed

Additional context

The following issue may be related: https://github.com/Dokploy/dokploy/issues/2558

The only workaround I could find was to use the external deploy-network network. But it forces to use app specific hostnames for the database to prevent conflict:

services:
  mongosh:
    image: alpine/mongosh:latest
    command: sh -c "mongosh 'mongodb://mongonet-mongo' && tail -f /dev/null"
    depends_on:
      - mongo
    networks: 
      - dokploy-network

  mongo:
    image: mongo:latest
    hostname: mongonet-mongo
    ports:
      - '27018:27017'
    command:
      - --storageEngine=wiredTiger
    volumes:
      - data:/data/db
    logging:
      driver: none
    networks:
      - dokploy-network

volumes:
  data:
  node_modules:

networks:
  dokploy-network:
    external: true

Connecting to:		mongodb://mongonet-mongo/?directConnection=true&appName=mongosh+2.0.2
Using MongoDB:		8.2.2
Using Mongosh:		2.0.2

Will you send a PR to fix it?

No

[Siumauricio]

I see they are connected and working fine (Using isolated deployment and not using it)

[loic-h]

Thanks for your response. I installed dokploy lcoally on my mac and can confirm that my reproduction code does work. Mongosh was able to connect to mongo. I suppose my issue comes then from my VPS config. I am on OVHCloud. After some research I wasn't able to pin-point the exact issue. I'll stick with the fix suggested in my original post. I'll close the topic as it has nothing to do with dokploy.