Handle lost connection to mongo db from nodejs

Question

I'm trying to get "connection lost" or something similar when connection lost between nodejs and mongodb server. I use native driver and has following code

var mongo = require('mongodb');
var server = new mongo.Server('host', 'port', {
    auto_reconnect: true,
    socketOptions: {
        keepAlive: 10,
        connectTimeoutMS: 1000,
        socketTimeoutMS: 0
    }
});
var db = new mongo.Db(
    'dbname',
    server,
    {
        w: 1,
        wtimeout: 1000,
        numberOfRetries: 100,
        auto_reconnect: true
    }
);

db.on('close', function () {
    console.log('Error...close');
});
db.on('error', function (err) {
    console.log('Error...error', err);
});
db.on('disconnect', function (err) {
    console.log('Error...disconnect', err);
});
db.on('disconnected', function (err) {
    console.log('Error...disconnected', err);
});
db.on('parseError', function (err) {
    console.log('Error...parse', err);
});
db.on('timeout', function (err) {
    console.log('Error...timeout', err);
});

db.collection('collectionName',function(err, collection){
    if(err){
        console.log('Error...collection', err);
        return;
    }

    // set breakpoint here and break connection to mongo db server  
    collection.insert({}, function (err, data) {
        if (err) {
            console.log('Error...insert', err);
        }
        console.log('Fine!');
    });
});

No timeout or error apear around 20 minutes and insert is freezed. After that I got "Error...insert" with connection lost error.

I tried to set socketTimeoutMS = 10000 and keepAlive = 1 for example, but socketTimeoutMS rise "timeout" event constantly after 10000 and doesn't take into account keepAlive settings or even queries to mongodb.

Also wtimeout works only if we have connection to mongodb server and has a longtime query. If connection is lost it doesn't works.

So how can I get event or err when I lost conneciton? Or reduce 20 minute query freeze?

Skiagraph

Answer 1

If have the mongodb server process running, run this example. After, if you stop the server process, you'll see Error...close being displayed. All possible events for the "on" function can be found here

var MongoClient = require('mongodb').MongoClient;

// Connect to the db
MongoClient.connect('mongodb://localhost:27017/exampleDb', function(err, db) {
  if(err) {
    return console.dir(err);
  }
  console.log('We are connected');
  // db.close();
  db.on('close', function () {
    console.log('Error...close');
  });
});

Daddylonglegs

Search keywords: node downtime offline disconnect reconnect detect notify monitor status (this answer took me forever to find) – Clarke

Do you know if this is fired during an intermittent disconnect / reconnect, or if it only occurs in the event of the server going offline / unreachable? – Glyptic

Answer 2

Check out this: https://thecodebarbarian.com/managing-connections-with-the-mongodb-node-driver.html

The big problem is the driver would buffer the queries forever and never return before connection recovery instead of failing them out, which could hang your program's execution if people not aware about this.

Ingrown