Nestjs on AWS Lambda (Serverless Framework) | How to access the event parameter? - node.js

Question

I'm hosting a Nestjs application on AWS Lambda (using the Serverless Framework).
Please note that the implementation is behind AWS API Gateway.
Question: How can I access to event parameter in my Nest controller?
This is how I bootstrap the NestJS server:
import { APIGatewayProxyHandler } from 'aws-lambda';
import { NestFactory } from '#nestjs/core';
import { AppModule } from './app.module';
import { Server } from 'http';
import { ExpressAdapter } from '#nestjs/platform-express';
import * as awsServerlessExpress from 'aws-serverless-express';
import * as express from 'express';
let cachedServer: Server;
const bootstrapServer = async (): Promise<Server> => {
const expressApp = express();
const adapter = new ExpressAdapter(expressApp);
const app = await NestFactory.create(AppModule, adapter);
app.enableCors();
await app.init();
return awsServerlessExpress.createServer(expressApp);
}
export const handler: APIGatewayProxyHandler = async (event, context) => {
if (!cachedServer) {
cachedServer = await bootstrapServer()
}
return awsServerlessExpress.proxy(cachedServer, event, context, 'PROMISE')
.promise;
};
Here is a function in one controller:
#Get()
getUsers(event) { // <-- HOW TO ACCESS event HERE?? This event is undefined.
return {
statusCode: 200,
body: "This function works and returns this JSON as expected."
}
I'm struggling to understand how I can access the event paramenter, which is easily accessible in a "normal" node 12.x Lambda function:
module.exports.hello = async (event) => {
return {
statusCode: 200,
body: 'In a normal Lambda, the event is easily accessible, but in NestJS its (apparently) not.'
};
};

Answer 1

Solution:
Add AwsExpressServerlessMiddleware to your setup during bootstrap:
const awsServerlessExpressMiddleware = require('aws-serverless-express/middleware')
app.use(awsServerlessExpressMiddleware.eventContext())
Note: The app.use should be before app.init()
Now the event and context object can be accessed:
var event = req.apiGateway.event;
var context = req.apiGateway.context;
Credits: This answer on SO