How to resolve UnhandledPromiseRejectionWarning in mongoose?

I'm trying to fetch data using mongoose.

So everytime i got to fetch the posts from the api -- localhost:3000/api/posts -- i get the foll error that i am unable to decypher.

(node:12100) UnhandledPromiseRejectionWarning: Unhandled promise rejection (r
ejection id: 1): [MongoError: connect ETIMEDOUT xxxx]

The foll is my code in the api.js file. I'd appreciate if you can provide guidance on where i am going wrong with this.

const express = require('express');
const router = express.Router();
const mongoose = require('mongoose');
const post = require('../models/post');

const db = "mongodb://<dbuser>:<dbpassword>@xxxxxxx.mlab.com:xxxxxx/xxxxxx";

mongoose.Promise = global.Promise;
mongoose.connect(db, function(err) {
    if(err) {
        console.log('Connection error');
    }
});

router.get('/posts', function(req, res) {
    console.log('Requesting posts');
    post.find({})
        .exec(function(err, posts) {
            if (err) {
                console.log('Error getting the posts');
            } else {
                res.json(posts);
                console.log(posts);
            }
        });
});
//in order for server.js file to access the api, we have to add the foll line
module.exports = router;

via Nosail