MongoServerSelectionError when attempting to connect to a Docker instance of MongoDB

Question

I pulled and am using the docker instance of MongoDB:

version: "3.4"

services:
  client:
    image: myApp:1.0
    ports:
      - "9001:4200"
  server:
    image: myServer:1.0
    ports:
      - "3000:3000"
    links:
      - database
  database:
    image: mongo
    volumes:
      - "/data/db:/data/db"
    ports:
      - "27017:27017"

In my Server code, I connect using:

const port = process.env.PORT || 3000;
const databaseURL = process.env.DATABASE_URL || 'mongodb://127.0.0.1:27017';

const server = http.createServer(app);
server.listen(port);
server.on('listening', async () => {
    console.info('Server is listening...');

    try {
        await MongoHelper.connect(databaseURL);
        console.info('Connected to MongoDB');
    } catch (err) {
        console.error(err);
    }
});

Running my server locally, it connects to the MongoDB just fine. However, when running my container, I get:

MongoServerSelectionError: connect ECONNREFUSED 127.0.0.1:27017
    at Timeout._onTimeout (/usr/src/app/node_modules/mongodb/lib/core/sdam/topology.js:430:30)
    at listOnTimeout (internal/timers.js:549:17)
    at processTimers (internal/timers.js:492:7) {
  reason: TopologyDescription {
    type: 'Single',
    setName: null,
    maxSetVersion: null,
    maxElectionId: null,
    servers: Map { '127.0.0.1:27017' => [ServerDescription] },
    stale: false,
    compatible: true,
    compatibilityError: null,
    logicalSessionTimeoutMinutes: null,
    heartbeatFrequencyMS: 10000,
    localThresholdMS: 15,
    commonWireVersion: null
  }
}

Any help would be greatly appreciated.

Answer 1

You can't directly access mongodb with the address 127.0.0.1:27017 . The database service will only be accessible with the resolution name database , the same name as the service.

So the connection string should be 'mongodb://database:27017' . You could define another alias if you want with:

links 
  - "database:database_alias"
environment:
  - DATABASE_URL="mongodb://database_alias:27017"

There are more details here .

Each container can now look up the hostname web or db and get back the appropriate container's IP address. For example, web's application code could connect to the URL postgres://db:5432 and start using the Postgres database.