Myujth

I have two apps:

• MongoDB (started from the Bitnami MongoDB Docker image)


• My custom node app

The two apps interact flawlessly when my node app is run natively. Now I've put it inside a Docker container and when I start both together with docker compose up, the backend can not connect to MongoDB.

This is an excerpt of the startup sequence:

mongodb_1 | 2018-11-10T22:22:52.481+0000 I NETWORK [initandlisten] waiting for connections on port 27017
[...]
backend_1 | 2018-11-10T22:23:48.119Z 'MongoNetworkError: failed to connect to server [localhost:27017] on first connect [MongoNetworkError: connect ECONNREFUSED 127.0.0.1:27017]'

This is my docker-compose.yml:

version: '2'
services:

 mongodb:
 image: bitnami/mongodb:latest
 expose:
 - 27017
 environment:
 - ALLOW_EMPTY_PASSWORD=yes

 backend:
 build: ./backend
 environment:
 API_HOST: http://localhost:3000/
 APP_SERVER_PORT: 3000
 expose:
 - 3000
 volumes:
 - ./backend:/app/backend
 links:
 - mongodb
 depends_on:
 - mongodb

This is my node call to the DB:

mongoose.connect('mongodb://localhost:27017/groceryList', 
 useNewUrlParser: true
);

I skimmed about 15 Stackoverflow questions asking the same and I am not getting the cause:

• It is not that MongoDB is not ready when my node app tries to
  connect. I wrapped my connection call into an auto reconnection
  function as described here and the error repeats endlessly. It is not just about the "first
  connect".


• I can publish Port 27017 of the MongoDB container and
  happily connect with Robo3T. The DB is definitely working.


• When I connect to mongodb://mongo:27017/groceryList instead, the same applies, only with the ENOTFOUND flag instead of ECONNREFUSED.

What am I missing?

• Docker 18.06.1-ce


• docker-compose 1.22.0


• Mongoose 5.3.6


• MongoDB 4.0.3


• Node 11.1.0


• macOS 10.14.1

Your mongodb service is named mongodb not mongo.

Try

mongoose.connect('mongodb://mongodb:27017/groceryList', 
 useNewUrlParser: true
);

The generic form is 'mongodb://mongoServiceName:27017/dbname', this uses docker's automatic dns resolution for containers within the same network.

And as you may already know from other questions/answers, within a container, the url is relative to itself, therefore since there not mongodb running inside the backend container, it can't connect to it.