gistfile1.js

var connectString = "mongodb://user:password@hostname_1:30000,hostname_2:30001,hostname_3:30002/admin?replicaSet=myset&autoReconnect=true";
var mongo = require('mongodb');
var async = require('async');
var admin_db;

var db1;
var db2;

var simpleQuery = function(callback) {
  if (db1==null) {
    db1 = admin_db.db('db1');
  }
  db1.collection('foo').findOne({}, function (err, results) {
    console.log(results);
    if (db2==null) {
      db2 = admin_db.db('db2');
    }
    db2.collection('bar').findOne({}, function (err, results) {
      console.log(results);
      setTimeout(callback, 2000);
    });
  });
}

mongo.connect(connectString, {db: {safe: true}}, function (err, db) {
  if (typeof err !== "undefined" && err !== null) {
    console.log (err);
  } else {
    admin_db = db;
    console.log('connected');
    async.whilst(
      function() {
        return true;
      },
      function(callback) {
        simpleQuery(callback);
      },
      function() {
        console.log("done");
      }
    );
  }
});