[MongoDb][Node.js] A simple demo to demonstrate Mongodb Replica Set's failover capability.

failover_insert_demo.js

/**
 * A sample demo to demonstrate Mongodb Replica Set's failover capability. 
 * Instructions:
 * 	1. Run your replica set servers.
 * 	2. Run this app (note: adjust the replica set's hosts & ports as you see them fit in your environments.)
 * 	3. Shutdown your replica set's primary node.
 * 	4. Watch the outputs of this running app. Confirm that the inserts are defered ( no errors being throws) when the primary node is downed and 
 * 		then come up again after a new primary node is elected in the replica set.
 */

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

// Notice the difference of connection string for connecting to a replica set and the usual one for connecting to a single mongodb server,
var connection_string = "mongodb://127.0.0.1:27018, 127.0.0.1:27019, 127.0.0.1:27020/demo_replica_set";

MongoClient.connect(connection_string, function(err, db){
	if (err) throw err;

	var document_value = 0;

	function insertDocument(){
		document_value++;
		var test_docs = db.collection("test_docs");		
		test_docs.insert({'value':document_value}, function(err, inserted){
			if (err) throw err;
			console.log("[INFO] - Successfully inserted "+JSON.stringify(inserted)+" document.");
		});

		console.log("[INFO] - Dispatched insert operation...");
		// Delayed for 1 sec then dispatch another insert.
		setTimeout(insertDocument, 1000);
	}

	insertDocument();
});