mongo_multiread.js

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

  var Logger = require('mongodb').Logger;
// Connection URL - Paste your db account connection string from Azure portal
var url = 'mongodb://prmultireadmongo:xxxx==@prmultireadmongo.mongo.cosmos.azure.com:10255/?ssl=true&replicaSet=globaldb&retrywrites=false&maxIdleTimeMS=120000&appName=@prmultireadmongo@';
// readTargetRegion - this will be used to read From while using Tags
var readFromRegion = "East US";

function doReads(client) {
//   setTimeout(readDefaultfunc, 1000, client);
//   setTimeout(readFromSecondaryfunc, 1000, client);
  setTimeout(readFromNearestfunc, 1000, client);
//   setTimeout(readFromRegionfunc, 1000, client, readFromRegion);
}

function readDefaultfunc(client) {
  var query = {};
  var readcoll = client.db('familiesdb').collection('families');
  readcoll.find(query).toArray(function(err, data) {
    assert.equal(null, err);
    console.log("readDefaultfunc query completed!");
  });
}

function readFromSecondaryfunc(client) {
  var query = {};
  var readcoll = client.db('familiesdb').collection('families');
  readcoll.find(query,{readPreference: ReadPreference.SECONDARY}).toArray(function(err, data) {
    assert.equal(null, err);
    console.log("readFromSecondaryfunc query completed!");
  });
}

function readFromNearestfunc(client) {
  var query = {};
  var readcoll = client.db('familiesdb',{readPreference: ReadPreference.NEAREST}).collection('families');
  readcoll.find(query).toArray(function(err, data) {
    assert.equal(null, err);
    console.log("readFromNearestfunc query completed!");
  });
}


function readFromRegionfunc(client, regionName) {
  var query = {};
  var readcoll = client.db('familiesdb').collection('families');
  readcoll.find(query,{readPreference: new ReadPreference(ReadPreference.SECONDARY_PREFERRED, {"region": regionName})}).toArray(function(err, data) {
    assert.equal(null, err);
    console.log("readFromRegionfunc query completed!");
  });
}

// Use connect method to connect to the server
MongoClient.connect(url, {
  autoReconnect : true,
//   readPreference: ReadPreference.NEAREST
}, function(err, client) {
  assert.equal(null, err);
  
  
  Logger.setLevel('debug');
  Logger.filter('class', ['Connection']);

  console.log("connected!");

  setInterval(doReads, 1000, client); 
});