How to properly connect to MongoDB using Cloud functions? - node.js

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.

Answer 1

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.