The Heroku app is having trouble communicating with the Mongo Atlas database, leading to frequent crashes

My deployed application on Heroku was working fine until I encountered an issue with the connection to my MongoDB Atlas database. Despite my attempts to resolve it, the application keeps crashing. The Heroku logs show the following:

"2022-12-05T10:19:21.000000+00:00 app[api]: Build succeeded
2022-12-05T10:19:24.577606+00:00 heroku[web.1]: Starting process with command `npm start`
2022-12-05T10:19:26.144610+00:00 app[web.1]: 
2022-12-05T10:19:26.144634+00:00 app[web.1]: > <a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="6b07021f1f070e0f092b5a455b455b">[email protected]</a> start
2022-12-05T10:19:26.144634+00:00 app[web.1]: > node index.js
2022-12-05T10:19:26.144635+00:00 app[web.1]: 
2022-12-05T10:19:26.369713+00:00 app[web.1]: Running on port: 36914
2022-12-05T10:19:26.725509+00:00 heroku[web.1]: State changed from starting to up
2022-12-05T10:19:56.365761+00:00 app[web.1]: Connected successfully to db server
2022-12-05T10:19:56.367567+00:00 app[web.1]: /app/node_modules/mongodb/lib/utils.js:698
2022-12-05T10:19:56.367568+00:00 app[web.1]:           throw error;
2022-12-05T10:19:56.367569+00:00 app[web.1]:           ^
2022-12-05T10:19:56.367569+00:00 app[web.1]: 
2022-12-05T10:19:56.367571+00:00 app[web.1]: TypeError: Cannot read properties of undefined (reading 'db')
2022-12-05T10:19:56.367571+00:00 app[web.1]:     at /app/dal.js:10:17
2022-12-05T10:19:56.367572+00:00 app[web.1]:     at /app/node_modules/mongodb/lib/utils.js:695:9
2022-12-05T10:19:56.367572+00:00 app[web.1]:     at /app/node_modules/mongodb/lib/mongo_client.js:285:23
2022-12-05T10:19:56.367573+00:00 app[web.1]:     at connectCallback (/app/node_modules/mongodb/lib/op...

package.json

{
  "name": "littledb",
  "version": "1.0.0",
  "description": "lowdb sample for 1.125",
  "main": "index.js",
  "scripts": {
    "start": "node index.js",
    "test": "jest"
  },
  "author": "<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="afcecdcac3efc2c6db81cacbda">[email protected]</a>",
  "license": "MIT",
  "dependencies": {
    "cors": "^2.8.4",
    "express": "^4.16.3",
    "http-server": "^14.1.1",
    "lowdb": "^1.0.0",
    "mongodb": "^3.7.3",
    "nodemon": "^2.0.20"
  },
  "devDependencies": {
    "@types/mongodb": "^4.0.7"
  }
}

dal.js

const MongoClient = require('mongodb').MongoClient;
const url         = 'mongodb://localhost:27017';
let db            = null;
 
// connect to mongo
MongoClient.connect(url, {useUnifiedTopology: true}, function(err, client) {
  
    db = client.db('baddestbank');
});

// create user account
function create(name, email, password){
    return new Promise((resolve, reject) => {    
        const collection = db.collection('users');
        
    })
}

// find user account
...

I have followed the instructions to resolve the issue with '@types/mongodb' in my VS Code but I'm still facing problems.

Despite having correct config vars on Heroku and MongoDB Atlas, my application is failing to sync data from the frontend to the MongoDB database. I have reviewed the IP address settings on Atlas as well.

The application functions correctly locally, but the deployment is causing the crashes. I have a deadline for my MIT project in 3 days, so I need to find a solution soon.

GitHub repository

The expected behavior was for the app to connect successfully to the database and allow users to access their accounts, but currently, it is failing to push data and authenticate users.

javascriptmongodbmongooseherokumongodb-atlas

Answer №1

Connecting to deployed databases can present challenges when hardcoded references are in place. Here are some helpful suggestions:

1 - Utilize environment variables or configuration specific to local development and production environments

  • Install dotenv npm i dotenv
  • Create an .env file in the root directory of your project
  • Add a line like this to the .env file - 
    DB_URI='mongodb://localhost:27017'
  • At the beginning of index.js or dal.js, include require('dotenv').config()
  • Avoid hardcoding the url in dal.js, instead use const url = process.env.DB_URI
  • In your Heroku configuration, set the DB_URI value for your production deployment. Refer to Heroku documentation

Why? Making changes to the DB url or other configurations within the code can be cumbersome. By adding variables to your environment in platforms like Heroku and your local machine, no code changes are necessary, resulting in a more robust system.

2 - Ensure your web server (or other critical tasks) only starts once the database connection is established

Create a function in dal.js that connects to the database and confirm that it is connected before allowing it to proceed

function connectToDB () {
  return new Promise((resolve) => {
    const url = process.env.DB_URI
    MongoClient.connect(url, { useUnifiedTopology: true }, function (err, client) {
      if (err) console.error(err)
      console.log('Connected successfully to db server')
      db = client.db('myproject')
      resolve()
    })
  })
}

Invoke this function before starting your web server, for example, at the end of index.js, implement the following:

const init = async () => {
  await dal.connectToDB()
  const port = process.env.PORT || 3000
  app.listen(port)
  console.log('Running on port: ' + port)
}
init()

Why? It's essential to wait for a confirmed connection before indicating readiness to process. While there may be exceptions, this remains a fundamental best practice.

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