Can't connect to exposed service

Description of problem

I'm trying to setup an Instance of Mongo-express via docker-compose to manage a MongoDB created by dokku-mongo.

I have the following docker-compose.yml file, basically just defining the Envvariables:

version: "3" 
services: 
  db-interface: 
    image: mongo-express 
    restart: "no" 
    ports: 
      - "5081:8081" 
    domainname: MY.DOMAIN.com 
    environment: 
      ME_CONFIG_MONGODB_ADMINUSERNAME: time_vault_staging_db
      ME_CONFIG_MONGODB_ADMINPASSWORD: some-created-passwd
      ME_CONFIG_MONGODB_URL: mongodb://my_mongo_staging_db:some-created-passwd@127.0.0.1:27017/

The dokku mongo:info of the my_mongo_staging_db is as follows:

=====> my_mongo_staging_db mongo service information
       Config dir:          /var/lib/dokku/services/mongo/my_mongo_staging_db/config
       Config options:       --storageEngine wiredTiger --auth 
       Data dir:            /var/lib/dokku/services/mongo/my_mongo_staging_db/data
       Dsn:                 mongodb://my_mongo_staging_db:some-created-passwd@dokku-mongo-my-mongo-staging-db:27017/my_mongo_staging_db
       Exposed ports:       27017->127.0.0.1:27017 27018->27018 27019->27019 28017->28017 
       Id:                  49557db0569e694654b1d6765b5ba099f775e6296db0d18d6de5820189874b11
       Internal ip:         172.20.0.7               
       Initial network:                              
       Links:               time-vault-staging       
       Post create network:                          
       Post start network:                           
       Service root:        /var/lib/dokku/services/mongo/time_vault_staging_db
       Status:              running                  
       Version:             mongo:7.0.2

As you can see i already exposed the dokku-mongo service to 127.0.0.1:27017.

However, when i try to start the Mongo Express app via docker-compose up I encouter:

db-interface_1  | /docker-entrypoint.sh: line 15: /dev/tcp/127.0.0.1/27017: Connection refused
db-interface_1  | Thu Apr  4 10:50:04 UTC 2024 retrying to connect to 127.0.0.1:27017 (2/10)
db-interface_1  | /docker-entrypoint.sh: connect: Connection refused

Did I do the Expose incorrectly or mix up the database credentials?

How reproducible

Use docker-compose.yml above. Create dokku-mongo service as usual. Expose Port 127.0.0.1:27017. Start App

Steps to Reproduce

1. 2. 3.

Actual Results

Mongo-Express App does not connect to dokku-mongo db.

Expected Results

Connection successfull and startup of Mongo-Express app.

Environment Information

`dokku report APP_NAME` output

It's a dokku-mongo service. Issueing this command yields in a ! App time_vault_staging_db does not exist message.

dokku / dokku-mongo