Hi! First of all, thank you so much for your help, I really appreciate it.
I’m working on my URL-shortener and everything works perfectly when I work with my local database, and with my mLab database on cloud9, but when I deploy my project to heroku, it gives me an error (503) and says that my application could not be served. It’s my first time deploying to Heroku using mongoDB
So… I decided to test if my app or my deployment process to heroku were causing the problem. I made a small sample program that inserts documents into my mLab database that works great on cloud9 to try deploying to heroku a simple program, but on heroku it doesn’t work, this is the message I get:
Application error
An error occurred in the application and your page could not be served. If you are the application owner, check your logs for details
But when I check on the logs and build log, there is no error, it says built finished.
The console says
Failed to load resource: the server responded with a status of 503 (Service Unavailable)
Here is my server.js code:
var express = require('express');
var mongo = require("mongodb").MongoClient;
var dataURL = process.env.MONGOLAB_URI;
var app = express();
app.get('/', function (req, res) {
res.writeHead(200, {'content-type':'application/JSON'});
mongo.connect(dataURL, function(err, db) {
if (err) throw err;
var collection = db.collection('data');
collection.insert({
"key" :"test"
}, function(err, data) {
if (err) throw err;
db.close();
res.end(JSON.stringify(data["ops"][0]));
});
});
})
app.listen(process.env.PORT, function () {
console.log('Example app listening on port!');
})
I declared an environment variable for my mLab URI and it works great on cloud9, on Heroku I added it using the settings tab as well.
And the port is defined by the environment, not fixed.
I seriously appreciate your help! Thank you! 
