How to properly connect to MongoDB using Cloud functions?

Question

I would like to connect to my Atlas cluster only once per instance running Cloud Functions.

Here is my code for an instance :

const MongoClient = require("mongodb").MongoClient;

const client = new MongoClient("myUrl", {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

exports.myHttpMethod = functions.region("europe-west1").runWith({
  memory: "128MB",
  timeoutSeconds: 20,
}).https.onCall((data, context) => {
  console.log("Data is: ", data);
  client.connect(() => {
    const testCollection = client.db("myDB").collection("test");
    testCollection.insertOne(data);
  });
});

And i would like to avoid the client.connect() in each function call that seems to be really too much.

I would like to do something like this :

const MongoClient = require("mongodb").MongoClient;

const client = await MongoClient.connect("myUrl", {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

const db = client.db("myDB");

exports.myHttpMethod = functions.region("europe-west1").runWith({
  memory: "128MB",
  timeoutSeconds: 20,
}).https.onCall((data, context) => {
  console.log("Data is: ", data);
  const testCollection = db.collection("test");
  testCollection.insertOne(data);
});

But i can't await like this.
In my AWS Lambda functions (running in python) i have not this issue and i am able to connect only once per instance, so i guess there is an equivalent but i don't know much JS / Node JS.

user_13130697 · Answer

You can store your database client as a global variable. From the documentation,

Cloud Functions often recycles the execution environment of a previous invocation. If you declare a variable in global scope, its value can be reused in subsequent invocations without having to be recomputed.

Try refactoring the code as shown below:

import * as functions from "firebase-functions";

import { MongoClient } from "mongodb"; 

let client: MongoClient | null;

const getClient = async () => {
  if (!client) {
    const mClient = new MongoClient("[MONGODB_URI]", {});
    client = await mClient.connect();
    functions.logger.log("Connected to MongoDB");
  } else {
    functions.logger.log("Using existing MongoDB connection");
  }
  functions.logger.log("Returning client");
  return client;
};

export const helloWorld = functions.https.onRequest(
  async (request, response) => {
    const db = (await getClient()).db("[DATABASE]");
    const result = await db.collection("[COLLECTION]").findOne({});
    response.send("Hello from Firebase!");
  }
);

This should reuse the connection for that instance.

How to properly connect to MongoDB using Cloud functions?

1 Answers