Error while deploying app on Heroku MongoDB connection - node.js

Question

I created the app using express and MongoDB. When I run the app locally it runs perfectly.I created a PostDB database on MongoDB atlas and generated and got connection string.I want to deploy this app using heroku but I don't why it gives this error.Please help me. Thanks in advance.
This is my connection string:
mongoose.connect("\mongodb+srv://Admin:minnu#mongodb01.irdlb.mongodb.net/PostDB",{useNewUrlParser:true,useCreateIndex:true, useUnifiedTopology: true},function(err,db){
if (err) {
console.log('Unable to connect to the server. Please start the server. Error:', err);
} else {
console.log('Connected to Server successfully!');
}});
This is the error I get:
2020-07-22T13:10:59.614060+00:00 app[web.1]: commonWireVersion: null
2020-07-22T13:10:59.614061+00:00 app[web.1]: }
2020-07-22T13:10:59.614061+00:00 app[web.1]: }
2020-07-22T13:10:59.631071+00:00 app[web.1]: Unable to connect to the server. Please start the server. Error: MongooseServerSelectionError: connect ECONNREFUSED 127.0.0.1:27017
2020-07-22T13:10:59.631074+00:00 app[web.1]: at NativeConnection.Connection.openUri (/app/node_modules/mongoose/lib/connection.js:828:32)
2020-07-22T13:10:59.631075+00:00 app[web.1]: at Mongoose.connect (/app/node_modules/mongoose/lib/index.js:335:15)
2020-07-22T13:10:59.631076+00:00 app[web.1]: at Object.<anonymous> (/app/Models/User.js:2:10)
2020-07-22T13:10:59.631076+00:00 app[web.1]: at Module._compile (internal/modules/cjs/loader.js:1138:30)
2020-07-22T13:10:59.631077+00:00 app[web.1]: at Object.Module._extensions..js (internal/modules/cjs/loader.js:1158:10)
2020-07-22T13:10:59.631077+00:00 app[web.1]: at Module.load (internal/modules/cjs/loader.js:986:32)
2020-07-22T13:10:59.631078+00:00 app[web.1]: at Function.Module._load (internal/modules/cjs/loader.js:879:14)
2020-07-22T13:10:59.631078+00:00 app[web.1]: at Module.require (internal/modules/cjs/loader.js:1026:19)
2020-07-22T13:10:59.631079+00:00 app[web.1]: at require (internal/modules/cjs/helpers.js:72:18)
2020-07-22T13:10:59.631079+00:00 app[web.1]: at Object.<anonymous> (/app/Routes/Posts.js:6:12)
2020-07-22T13:10:59.631079+00:00 app[web.1]: at Module._compile (internal/modules/cjs/loader.js:1138:30)
2020-07-22T13:10:59.631080+00:00 app[web.1]: at Object.Module._extensions..js (internal/modules/cjs/loader.js:1158:10)
2020-07-22T13:10:59.631080+00:00 app[web.1]: at Module.load (internal/modules/cjs/loader.js:986:32)
2020-07-22T13:10:59.631081+00:00 app[web.1]: at Function.Module._load (internal/modules/cjs/loader.js:879:14)
2020-07-22T13:10:59.631081+00:00 app[web.1]: at Module.require (internal/modules/cjs/loader.js:1026:19)
2020-07-22T13:10:59.631081+00:00 app[web.1]: at require (internal/modules/cjs/helpers.js:72:18) {
2020-07-22T13:10:59.631082+00:00 app[web.1]: reason: TopologyDescription {
2020-07-22T13:10:59.631082+00:00 app[web.1]: type: 'Single',
2020-07-22T13:10:59.631083+00:00 app[web.1]: setName: null,
2020-07-22T13:10:59.631083+00:00 app[web.1]: maxSetVersion: null,
2020-07-22T13:10:59.631083+00:00 app[web.1]: maxElectionId: null,
2020-07-22T13:10:59.631084+00:00 app[web.1]: servers: Map { 'localhost:27017' => [ServerDescription] },
2020-07-22T13:10:59.631084+00:00 app[web.1]: stale: false,
2020-07-22T13:10:59.631085+00:00 app[web.1]: compatible: true,
2020-07-22T13:10:59.631085+00:00 app[web.1]: compatibilityError: null,
2020-07-22T13:10:59.631086+00:00 app[web.1]: logicalSessionTimeoutMinutes: null,
2020-07-22T13:10:59.631086+00:00 app[web.1]: heartbeatFrequencyMS: 10000,
2020-07-22T13:10:59.631086+00:00 app[web.1]: localThresholdMS: 15,
2020-07-22T13:10:59.631087+00:00 app[web.1]: commonWireVersion: null
2020-07-22T13:10:59.631087+00:00 app[web.1]: }
2020-07-22T13:10:59.631087+00:00 app[web.1]: }
2020-07-22T13:11:29.817201+00:00 heroku[web.1]: State changed from starting to up
2020-07-22T13:43:44.978055+00:00 heroku[web.1]: Idling
2020-07-22T13:43:44.980176+00:00 heroku[web.1]: State changed from up to down
2020-07-22T13:43:46.293776+00:00 heroku[web.1]: Stopping all processes with SIGTERM
2020-07-22T13:43:46.385591+00:00 heroku[web.1]: Process exited with status 143
2020-07-22T15:23:20.000000+00:00 app[api]: Build started by user mamadgiaishwarya#gmail.com
2020-07-22T15:23:41.274124+00:00 app[api]: Deploy 9e2202b9 by user mamadgiaishwarya#gmail.com
2020-07-22T15:23:41.274124+00:00 app[api]: Release v9 created by user mamadgiaishwarya#gmail.com
2020-07-22T15:23:41.454375+00:00 heroku[web.1]: State changed from down to starting
2020-07-22T15:23:42.000000+00:00 app[api]: Build succeeded
2020-07-22T15:23:43.755247+00:00 heroku[web.1]: Starting process with command `npm start`
2020-07-22T15:23:46.020199+00:00 app[web.1]:
2020-07-22T15:23:46.020218+00:00 app[web.1]: > ejs-challenge#1.0.0 start /app
2020-07-22T15:23:46.020219+00:00 app[web.1]: > node app.js
2020-07-22T15:23:46.020219+00:00 app[web.1]:
2020-07-22T15:23:46.753513+00:00 app[web.1]: Warning: connect.session() MemoryStore is not
2020-07-22T15:23:46.753525+00:00 app[web.1]: designed for a production environment, as it will leak
2020-07-22T15:23:46.753554+00:00 app[web.1]: memory, and will not scale past a single process.
2020-07-22T15:23:46.770376+00:00 app[web.1]: Server started on port 3000
2020-07-22T15:23:47.305407+00:00 heroku[web.1]: State changed from starting to up
2020-07-22T15:23:48.056394+00:00 app[web.1]: Connected to Server successfully!
2020-07-22T15:23:48.059001+00:00 app[web.1]: Connected to Server successfully!
2020-07-22T15:24:25.538134+00:00 heroku[router]: at=info method=GET path="/" host=shielded-citadel-75286.herokuapp.com request_id=a2276768-c8b4-4937-a8f9-feb2e1cc9d00 fwd="106.200.146.62" dyno=web.1 connect=0ms service=1360ms status=200 bytes=4199 protocol=https
2020-07-22T15:24:26.201469+00:00 heroku[router]: at=info method=GET path="/css/styles.css" host=shielded-citadel-75286.herokuapp.com request_id=1d330f4c-66fd-407c-a8ed-57ba80507318 fwd="106.200.146.62" dyno=web.1 connect=1ms service=9ms status=200 bytes=2179 protocol=https
2020-07-22T15:24:26.284481+00:00 heroku[router]: at=info method=GET path="/images/logo.jpg" host=shielded-citadel-75286.herokuapp.com request_id=96a94f69-2984-4b7f-8e5e-1ae6f12493e6 fwd="106.200.146.62" dyno=web.1 connect=0ms service=11ms status=200 bytes=8897 protocol=https
2020-07-22T15:24:26.318935+00:00 heroku[router]: at=info method=GET path="/images/butterfly.gif" host=shielded-citadel-75286.herokuapp.com request_id=f54f11ef-31a4-4fdf-ad7f-c5d47c354afb fwd="106.200.146.62" dyno=web.1 connect=0ms service=45ms status=200 bytes=687572 protocol=https
2020-07-22T15:24:51.370552+00:00 heroku[router]: at=info method=GET path="/favicon.ico" host=shielded-citadel-75286.herokuapp.com request_id=396f3ab9-b44b-4432-888e-792eb45268e2 fwd="106.200.146.62" dyno=web.1 connect=0ms service=5ms status=404 bytes=394 protocol=https
2020-07-22T15:26:13.000000+00:00 app[api]: Build started by user mamadgiaishwarya#gmail.com
2020-07-22T15:26:35.089490+00:00 app[api]: Release v10 created by user mamadgiaishwarya#gmail.com
2020-07-22T15:26:35.089490+00:00 app[api]: Deploy 7fd231d2 by user mamadgiaishwarya#gmail.com
2020-07-22T15:26:36.000000+00:00 app[api]: Build succeeded
2020-07-22T15:26:36.726907+00:00 heroku[web.1]: Restarting
2020-07-22T15:26:36.741521+00:00 heroku[web.1]: State changed from up to starting
2020-07-22T15:26:37.654962+00:00 heroku[web.1]: Stopping all processes with SIGTERM
2020-07-22T15:26:37.782161+00:00 heroku[web.1]: Process exited with status 143
2020-07-22T15:26:39.941929+00:00 heroku[web.1]: Starting process with command `npm start`
2020-07-22T15:26:42.451886+00:00 app[web.1]:
2020-07-22T15:26:42.451908+00:00 app[web.1]: > ejs-challenge#1.0.0 start /app
2020-07-22T15:26:42.451908+00:00 app[web.1]: > node app.js
2020-07-22T15:26:42.451909+00:00 app[web.1]:
2020-07-22T15:26:43.528332+00:00 app[web.1]: Warning: connect.session() MemoryStore is not
2020-07-22T15:26:43.528343+00:00 app[web.1]: designed for a production environment, as it will leak
2020-07-22T15:26:43.528344+00:00 app[web.1]: memory, and will not scale past a single process.
2020-07-22T15:26:43.537025+00:00 app[web.1]: Server started on port 3000
2020-07-22T15:26:43.977021+00:00 heroku[web.1]: State changed from starting to up
2020-07-22T15:26:44.829130+00:00 app[web.1]: Connected to Server successfully!
2020-07-22T15:26:44.831445+00:00 app[web.1]: Connected to Server successfully!
2020-07-22T15:28:23.000000+00:00 app[api]: Build started by user mamadgiaishwarya#gmail.com
2020-07-22T15:28:45.263212+00:00 app[api]: Deploy c7cbd9d0 by user mamadgiaishwarya#gmail.com
2020-07-22T15:28:45.263212+00:00 app[api]: Release v11 created by user mamadgiaishwarya#gmail.com
2020-07-22T15:28:45.446526+00:00 heroku[web.1]: Restarting
2020-07-22T15:28:45.448387+00:00 heroku[web.1]: State changed from up to starting
2020-07-22T15:28:46.000000+00:00 app[api]: Build succeeded
2020-07-22T15:28:46.651703+00:00 heroku[web.1]: Stopping all processes with SIGTERM
2020-07-22T15:28:46.746865+00:00 heroku[web.1]: Process exited with status 143
2020-07-22T15:28:49.098450+00:00 heroku[web.1]: Starting process with command `npm start`
2020-07-22T15:28:51.924571+00:00 app[web.1]:
2020-07-22T15:28:51.924589+00:00 app[web.1]: > ejs-challenge#1.0.0 start /app
2020-07-22T15:28:51.924589+00:00 app[web.1]: > node app.js
2020-07-22T15:28:51.924589+00:00 app[web.1]:
2020-07-22T15:28:52.898117+00:00 app[web.1]: Warning: connect.session() MemoryStore is not
2020-07-22T15:28:52.898161+00:00 app[web.1]: designed for a production environment, as it will leak
2020-07-22T15:28:52.898162+00:00 app[web.1]: memory, and will not scale past a single process.
2020-07-22T15:28:52.905188+00:00 app[web.1]: Server started on port 3000
2020-07-22T15:28:53.428020+00:00 heroku[web.1]: State changed from starting to up

Answer 1

I think you have a mistake in your connection string.
According to MongoDB docs, connection string should start with mongodb://, not with the leading \ in the front.
I also recommend you to use Promises or Async/Await for your connections, like the following snippet below:
// Start connection via Mongoose.
mongoose
.connect(YOUR_CONNECTION_STRING, {
useNewUrlParser: true,
useCreateIndex: true,
useFindAndModify: false,
useUnifiedTopology: true,
})
.then(() => {
console.log('Database connected successfully!');
})
.catch((err) => {
console.log('Error connecting with error code:', err);
});
app.listen(PORT, () => {
console.log('Server starts at port...');
}
It makes code much easier to read.
Alternatively, do you have any exceptions that you do not catch before connecting to the database? It might bubble up and crash your database connection for security reasons.