Part of https://gist.github.com/jgcmarins/5a61d097bae18d50110b1b3c2005b3da

index.lambda.ts

import { createServer, proxy } from 'aws-serverless-express';

import connectDatabase from './database';

import app from './app';

export const handler = (event, ctx) => {
  // This will re-use `cachedMongoConn` between function calls.
  // See https://www.mongodb.com/blog/post/serverless-development-with-nodejs-aws-lambda-mongodb-atlas
  // See https://docs.atlas.mongodb.com/best-practices-connecting-to-aws-lambda/
  // https://mongoosejs.com/docs/lambda.html
  ctx.callbackWaitsForEmptyEventLoop = false;

  console.log('Connecting to database...');
  connectDatabase()
    .then(() => proxy(createServer(app.callback()), event, ctx))
    .catch(error => {
      console.error('Could not connect to database', { error });
      throw error;
    });
};