Gateway Timeout on Express.js

I have an amazing problem! As I mentioned in title, Main problem is Gateway timeout but as soon as I logged in on my server the web page received data; Without stop and start my app!

Server:

I am using Ubuntu 14.04.5(GNU/Linux 4.4.0-62-generic x86_64)

Code:

I am using pm2 to run my node.js application;

The express code to run server is:

var app = http.createServer(function(req, res) {
 try {
   var basePath = __dirname +  "/html";
   var filePath = basePath + req.url;
   var contentType = 'text/html';
   var extname = path.extname('filePath');
   switch (extname) {
       case '.js':
           contentType = 'text/javascript';
           basePath = __dirname  + '/js'
           break;
       case '.css':
           contentType = 'text/css';
           basePath = __dirname + '/css'

           break;
   }
   if (filePath == basePath + "/") {
    filePath = filePath + "login.html";
 }

   var page = fs.readFileSync(filePath);
   res.end(page);

 }
 catch(err) {
   console.log(error);
 }
}).listen( constants.httpPort, constants.ip, function() {
  console.log('Node Runs on' + process.env.OPENSHIFT_NODEJS_PORT + ' ' + process.env.OPENSHIFT_NODEJS_IP);
  console.log('Listening on ' + constants.httpPort + ' ' +  constants.ip);
});

I am not sure what is my problem, It is my server side and Its configuration or my code has missed a point; Really I am confused Why page load just by log in server?

via Fa.Shapouri