Using Mongoose With AWS Lambda

AWS Lambda is a popular service for running arbitrary functions without managing individual servers. Using Mongoose in your AWS Lambda functions is easy. Here's a sample function that connects to a MongoDB instance and finds a single document:

const mongoose = require('mongoose');
let conn = null;
const uri = 'YOUR CONNECTION STRING HERE';
exports.handler = async function(event, context) {
 // Make sure to add this so you can re-use `conn` between function calls.
 // See https://www.mongodb.com/blog/post/serverless-development-with-nodejs-aws-lambda-mongodb-atlas
 context.callbackWaitsForEmptyEventLoop = false;
 // Because `conn` is in the global scope, Lambda may retain it between
 // function calls thanks to `callbackWaitsForEmptyEventLoop`.
 // This means your Lambda function doesn't have to go through the
 // potentially expensive process of connecting to MongoDB every time.
 if (conn == null) {
 conn = mongoose.createConnection(uri, {
 // and tell the MongoDB driver to not wait more than 5 seconds
 // before erroring out if it isn't connected
 serverSelectionTimeoutMS: 5000
 });
 // `await`ing connection after assigning to the `conn` variable
 // to avoid multiple function calls creating new connections
 await conn.asPromise();
 conn.model('Test', new mongoose.Schema({ name: String }));
 }
 const M = conn.model('Test');
 const doc = await M.findOne();
 console.log(doc);
 return doc;
};

Connection Helper

The above code works fine for a single Lambda function, but what if you want to reuse the same connection logic in multiple Lambda functions? You can export the below function.

const mongoose = require('mongoose');
let conn = null;
const uri = 'YOUR CONNECTION STRING HERE';
exports.connect = async function() {
 if (conn == null) {
 conn = mongoose.createConnection(uri, {
 serverSelectionTimeoutMS: 5000
 });
 // `await`ing connection after assigning to the `conn` variable
 // to avoid multiple function calls creating new connections
 await conn.asPromise();
 }
 return conn;
};

Using mongoose.connect()

You can also use mongoose.connect(), so you can use mongoose.model() to create models.

const mongoose = require('mongoose');
let conn = null;
const uri = 'YOUR CONNECTION STRING HERE';
exports.connect = async function() {
 if (conn == null) {
 conn = mongoose.connect(uri, {
 serverSelectionTimeoutMS: 5000
 }).then(() => mongoose);
 // `await`ing connection after assigning to the `conn` variable
 // to avoid multiple function calls creating new connections
 await conn;
 }
 return conn;
};