How do I manage MongoDB connections in a Node js web application

Question

I'm creating a website with MongoDB and the node-mongodb-native driver.

I'd want to know how to manage connections and have a few questions:

Is it sufficient to use a single MongoDB connection for all requests? Are there any concerns with performance? If not, can I create a global connection that I can utilise throughout the application?

If not, is it okay if I start a new connection when a request comes in and terminate it when the request is completed? Is it costly to establish and maintain a connection?

Is it necessary to use a global connection pool? According to what I've heard, the driver has a built-in connection pool. Is it a wise decision?

How many connections should I utilise if I use a connection pool?

Is there anything else I should be aware of?

Answer 1

When the Node.js application starts, create a new connection and utilise the old database connection object:

/server.js

import express from 'express';
import Promise from 'bluebird';
import logger from 'winston';
import { MongoClient } from 'mongodb';
import config from './config';
import usersRestApi from './api/users';

const app = express();

app.use('/api/users', usersRestApi);

app.get('/', (req, res) => {
  res.send('Hello World');
});

// Create a MongoDB connection pool and start the application
// after the database connection is ready
MongoClient.connect(config.database.url, { promiseLibrary: Promise }, (err, db) => {
  if (err) {
    logger.warn(`Failed to connect to the database. ${err.stack}`);
  }
  app.locals.db = db;
  app.listen(config.port, () => {
    logger.info(`Node.js app is listening at http://localhost:${config.port}`);
  });
});

/api/users.js

import { Router } from 'express';
import { ObjectID } from 'mongodb';

const router = new Router();

router.get('/:id', async (req, res, next) => {
  try {
    const db = req.app.locals.db;
    const id = new ObjectID(req.params.id);
    const user = await db.collection('user').findOne({ _id: id }, {
      email: 1,
      firstName: 1,
      lastName: 1
    });

    if (user) {
      user.id = req.params.id;
      res.send(user);
    } else {
      res.sendStatus(404);
    }
  } catch (err) {
    next(err);
  }
});

export default router;

Source: How to Open Database Connections in a Node.js/Express App

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