it will work well in localhost, when ever i deploy it on to server, registration form doesnot responding??

Here is my code:

var express = require('express'),
    http = require('http'),
    path = require('path'),
   hash = require('./pass').hash;
var moment = require('moment');
var bcrypt = require('bcrypt');
var app = express();
var methodOverride = require('method-override');
var mysql      = require('mysql');
connection.connect(function(err){
if(!err) {
    console.log("Database is connected ... nn");
} else {
    console.log("Error connecting database ... nn");
}
});
/*
Middlewares and configurations 
*/
app.configure(function () {
    app.use(express.bodyParser());
    app.use(express.cookieParser('Authentication Tutorial '));
  app.use(express.session());
    app.use(methodOverride(function(req, res){
 if (req.body && typeof req.body == 'object' && '_method' in req.body) 
 { 
  var method = req.body._method;
  delete req.body._method;
  return method;
} 
}));
    app.use(express.static(path.join(__dirname, 'public')));
    app.set('views', __dirname + '/views');
    app.set('view engine', 'ejs');
});
var connection = mysql.createConnection({
  host     : 'hostss',
  user     : 'user',
  password : 'password*',
  database : 'db'
});
app.use(function (req, res, next) {
    var err = req.session.error,
        msg = req.session.success;
    delete req.session.error;
    delete req.session.success;
    res.locals.message = '';
    if (err) res.locals.message = '<p class="msg error">' + err + '</p>';
    if (msg) res.locals.message = '<p class="msg success">' + msg + '</p>';
    next();
});
/*
Helper Functions
*/

function user_exits(req, res, next) { 
  var username= req.body.username;
 connection.query("SELECT * FROM user WHERE username =?",[username],function (error, results, fields) {
if (error) {
    console.log(error);
    res.send("fail internal error"+"\r\n");
}
if (results.length >0) {
    console.log('User is Already Exists');
    res.send("fail user already exists"+"\r\n");

} else {


        console.log('No user Available oN that name, U can insert it');
        next();
}

 });
}
                  
/*
Routes
*/
app.get("/", function (req, res) {

        res.render("index", { moment: moment });
    
});

app.get("/signup", function (req, res) {
        res.render("signup",{ moment: moment });
    
});

app.post("/signup",user_exits,function (req, res){
    bcrypt.hash(req.body.password, 5, function( err, bcryptedPassword) {
   
   var users={
     "username":req.body.username,
      "email":req.body.email,
     "password":bcryptedPassword,
     
   } 
   console.log(users);
   connection.query('INSERT INTO user SET ?',users, function (error, results, fields) {
  if (error) {
    console.log("error ocurred",error);
    res.send({
      "code":400,
      "failed":"error ocurred"
    });
  }else{
    console.log('The solution is: ', results);
    res.send({
      "code":200,
      "success":"user registered sucessfully"
        });
  }
  });
  });
    
   
});

app.get("/login", function (req, res) {
    res.render("login",{ moment: moment });
});

app.post("/login",function (req, res) {
   var sess = req.session;
      var username= req.body.username;
  var password = req.body.password;
  connection.query('SELECT * FROM user WHERE username = ?',[username], function (error, results, fields) {
  if (error) {
   console.log(error);
  }else{
    if(results.length >0){
      bcrypt.compare(password, results[0].password, function(err, doesMatch){
        if (doesMatch){
             req.session.userId = results[0].id;
            req.session.user = results[0];
            console.log(results[0].id);
     res.redirect('/profile/'+results[0].id);
      }else{
     res.send({
       "code":204,
       "success":"Email and password does not match"
         });
      }
    });
    }
    else{
      console.log("fine");
    }
  }
  });
});

But when I upload it on DigitalOcean server the form is not working? please developer help me to fix that problem.