Reliably reconnect to MongoDB

Question

UPDATE: I am using the 2.1 version on the driver, against 3.2

I have a node application that uses MongoDB. The problem I have is that if the MongoDB server goes down for any reason, the application doesn't reconnect. To get this right, I based my tests on the code in this official tutorial.

var MongoClient = require('mongodb').MongoClient
  , f = require('util').format;

MongoClient.connect('mongodb://localhost:27017/test', 

// Optional: uncomment if necessary
// { db: { bufferMaxEntries: 3 } },


function(err, db) {
  var col = db.collection('t');

  setInterval(function() {
    col.insert({a:1}, function(err, r) {
      console.log("insert")
      console.log(err)

      col.findOne({}, function(err, doc) {
        console.log("findOne")
        console.log(err)
      });
    })
  }, 1000)
});

The idea is to run this script, and then stop mongod, and then restart it. So, here we go:

TEST 1: stopping mongod for 10 seconds

Stopping MongoDb for 10 seconds does the desired result: it will stop running the queries for those 10 seconds, and then will run all of them once the server is back ip

TEST 2: stopping mongod for 30 seconds

After exactly 30 seconds, I start getting:

{ [MongoError: topology was destroyed] name: 'MongoError', message: 'topology was destroyed' }
insert

{ [MongoError: topology was destroyed] name: 'MongoError', message: 'topology was destroyed' }

The trouble is that from this on, when I restart mongod, the connection is not re-establised.

Solutions?

Does this problem have a solution? If so, do you know what it is? Once my app starts puking "topology was destroyed", the only way to get everything to work again is by restarting the whole app...

Answer 1

With mongodb driver 3.1.10, you can set up your connection as

MongoClient.connect(connectionUrl, {
    reconnectInterval: 10000, // wait for 10 seconds before retry
    reconnectTries: Number.MAX_VALUE, // retry forever
}, function(err, res) {
    console.log('connected') 
})

You do not have to specify autoReconnect: true as that's the default.