The MongoClient is never closed, is this optional?

[frouo]

Hi there,

I'm working on implementing MongoDB into my Next.js project. Thanks for this starter.

I was curious why is the Mongo client never closed anywhere? is client.close() optional even for production?

As far as I understand, there is no need to close in development mode since the module is kept across reloads. But what about production especially when the project is hosted on Vercel (which uses serverless functions)?

Thanks in advance for your help 🙏

import { MongoClient } from 'mongodb';

export default async function handler(req, res) {
  const client = await MongoClient.connect(process.env.MONGODB_URI);
  const db = client.db();

  const collection = db.collection('users');
  const users = await collection.find().toArray();

  await client.close() // <- is this important for production?

  res.status(200).json(users);
}

[frouo]

Ok so anyway, I have tried and push the code without closing the client in production and boom, in less than 12 hours I have received a notification from mongo atlas:

[smaeda-ks]

@frouo have you tried setting the maxIdleTimeMS option?
https://www.mongodb.com/docs/drivers/node/current/fundamentals/connection/connection-options/

Specifies the amount of time, in milliseconds, a connection can be idle before it's closed. Specifying 0 means no minimum.

and its default is 0, as per their documentation above. So maybe setting it to a reasonable value (and adjust maxPoolSize)?

[forbesd7]

@frouo
I was running into this issue as well - I don't think you need to close the connections as it seems like they close automatically after not being used for a certain amount of time. Will continue to monitor connections as i test and see if this code should be adjusted to close the connection with each request.

I changed the mongodb.ts file to the following code and this seems to have fixed my issue.

(Taken from this site)

import { MongoClient } from 'mongodb';

declare global {
  var _mongoClientPromise: Promise<MongoClient>;
}


const uri = process.env.MONGODB_URI || '';
const options = {};

let client;
let clientPromise;

if (!process.env.MONGODB_URI) {
  throw new Error('Add Mongo URI to .env.local');
}

if (process.env.NODE_ENV === 'development') {
  if (!global._mongoClientPromise) {
    console.log('getting client');
    client = new MongoClient(uri, options);
    global._mongoClientPromise = client.connect();
  }
  clientPromise = global._mongoClientPromise;
} else {
  client = new MongoClient(uri, options);
  clientPromise = client.connect();
}

export default clientPromise;

Just a note - this is ONLY when i'm testing on local. No idea how so many connections were being made. You can see the giant reduction in connections after I change to this code.

[smaeda-ks]

we also have this example, fyi: https://github.com/vercel/mongodb-starter/blob/main/lib/mongodb.ts

[forbesd7]

@smaeda-ks Right, i was using that but it was creating a bunch of connections - i removed that code and added the one above which reduced the connection amount by a lot.

[smaeda-ks]

Ah, ok. I'll have some tests later and see if I can fix that.

[frouo]

@smaeda-ks no, I haven't touched to maxIdleTimeMS or any other setting as I would expect mongodb to work kinda out-of-the-box.

I was wondering, does the Vercel <> MongoDB integration fix this connection issue somehow? Does it auto-config mongodb atlas to "fit" the nextjs serverless environment?

[frouo]

Sorry, I'm rephrasing. I don't expect MongoDB to work out-of-the-box with Next.js, but I'm not confident in changing MongoDB configurations when no tutorial does (especially considering the Vercel MongoDB starter).

This actually surprises me because, as I mentioned earlier, as soon as I released the sample code above, I received a "connections exceeded" warning from MongoDB 🤷‍♂️ It's clear that using MongoDB out-of-the-box does not work, but there is no documentation on Vercel on how to configure MongoDB correctly.

Is maxIdleTimeMS the way to go? If so, what value does Vercel recommend? Thank you very much :)