No disconnected event when MongoDB docker container closed v5.7.3

[shaneguayCanopy]

This is an interesting issue in that the 'disconnected' event is never triggered when the MongoDB is brought down. We are running MongoDB through a Docker container and running a local node.js file.

We are using the latest Mongoose version 5.7.3.

When we tried an older version 5.0.12 it works. We found a similar issue that was described as being fixed in 5.0.12 from this ticket ("error event not triggered #6131") and indeed in 5.0.12 we did properly receive the 'disconnected' event when we closed the MongoDB container.

So it seems this bug has regressed and is back in latest version

mongoose.connection.on('disconnected', () => { console.log('DISCONNECTED!'); });

[shaneguayCanopy]

We've tracked the issue down to the use of the useUnifiedTopology: true setting in the connect method.

When we remove this option it works in the latest Mongoose version 5.7.3.

mongoose.connect(dbConnectionString, {
        useNewUrlParser: true,
        useFindAndModify: false,
        autoReconnect: false,
        autoIndex: false,
        //useUnifiedTopology: true,
        bufferMaxEntries: 0
    }).then

[vkarpov15]

I'm unable to repro this. Below script prints out 'disconnected' in 5.7.3 when I shut down my local mongod instance.

'use strict';

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

mongoose.set('debug', true);

run().catch(error => console.log(error));

async function run() {
  await mongoose.connect('mongodb://localhost:27017/test', {
    useNewUrlParser: true,
    useUnifiedTopology: true,
    autoReconnect: false,
    bufferMaxEntries: 0
  });

  mongoose.connection.on('disconnected', () => console.log('Disconnected!'));

  console.log('Connected');
}

We also have test cases for this, and they pass on travis:

mongoose/test/connection.test.js

Lines 183 to 211 in cdfb507

	it('disconnected (gh-5498) (gh-5524)', function(done) {
	this.timeout(60000);
	let numConnected = 0;
	let numDisconnected = 0;
	let numReconnected = 0;
	let numReconnect = 0;
	let numClose = 0;
	const conn = mongoose.createConnection('mongodb://localhost:27000/mongoosetest', {
	useNewUrlParser: true,
	useUnifiedTopology: true
	});
	conn.on('connected', function() {
	++numConnected;
	});
	conn.on('disconnected', function() {
	++numDisconnected;
	});
	conn.on('reconnect', function() {
	++numReconnect;
	});
	// Same as `reconnect`, just for backwards compat
	conn.on('reconnected', function() {
	++numReconnected;
	});
	conn.on('close', function() {
	++numClose;
	});

.

What docker image are you using? Are you using docker compose? Also, does this issue happen without Docker?

[xinyangyuan]

The connection events also not firing when running node locally (mongoose version 5.7.5) and using MongoDB atlas. Simulate connection lost by manual computer internet connection, and none of the following events would fire:

mongoose.connection.on('disconnected', function(e) {
  console.log('Disconnected: ' + e);
});
mongoose.connection.on('error', function(e) {
  console.log('Error: ' + e);
});
mongoose.connection.on('timeout', function(e) {
  console.log('Timeout: ' + e);
});

ps: not sure manual disconnect internet is the right way to simulate, but also experience connection lost without any error when the nodejs is hosted in ec2.

[vkarpov15]

@xinyangyuan the below script fires 'disconnected' correctly for me when I turn off wifi on my macbook, it just takes maybe 30 seconds or so.

'use strict';

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

run().catch(error => console.log(error));

async function run() {
  await mongoose.connect('mongodb+srv://USER:PASS@cluster0-OMITTED.mongodb.net/test?retryWrites=true&w=majority', {
    useNewUrlParser: true,
    useUnifiedTopology: true,
    autoReconnect: false,
    bufferMaxEntries: 0
  });
mongoose.connection.on('disconnected', function(e) {
  console.log('Disconnected: ' + e);
});
mongoose.connection.on('error', function(e) {
  console.log('Error: ' + e);
});
mongoose.connection.on('timeout', function(e) {
  console.log('Timeout: ' + e);
});

  console.log('Connected');
}

Please make sure you give it some time to fire the disconnected event, it won't happen immediately.