Access to aws-lambda context when running nodejs + expressjs

Question

I'm, just starting out with AWS-Lambda, AWS-API Gateway and ExpressJs. I'm having trouble finding how the AWS-Lambda "context" is available in my "ExpressJs" application.

I'm using:

AWS-Lambda
AWS-API Gateway
NodeJs v4.3.2
ExpressJs 4.14.1
ClaudiaJs 2.7.0

In Aws Lambda I use aws-serverless-express to receive the API-Gateway request and initialize the node application. The following is the structure I have found from different tutorials, etc

lambda.js (Initiated from API-Gateway. Supplying the "context" variable in the call to "app.js")

'use strict'
const awsServerlessExpress = require('aws-serverless-express')
const app = require('./app')
const server = awsServerlessExpress.createServer(app)
exports.handler = (event, context) => awsServerlessExpress.proxy(server, event, context)

The core of my app.js express is:

var express = require('express');
...
var app = express();
...
app.use('/', index);
...
module.exports = app;

My questions:

Is there a way to access the AWS-Lambda "context" with this structure?
If not, what would be the best "pattern" to make it available?

Any input appreciated.

Jason · Accepted Answer · 2024-04-19 23:33:41Z

19

From v4.0 you need to use getCurrentInvoke as described in @cooow's answer.

Prior versions supported serverless-express/middleware:

... which exposes the event and context objects. You add it like this:

const awsServerlessExpressMiddleware = require('aws-serverless-express/middleware')
app.use(awsServerlessExpressMiddleware.eventContext())

Once this middleware is configured the event and context objects will be added to the request. You access those objects like so:

var event = req.apiGateway.event;
var context = req.apiGateway.context;

edited Apr 19, 2024 at 23:33

Jason

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answered Feb 24, 2017 at 15:01

Mark B

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1 Comment

Koniak Over a year ago

Thx, Works fine. A few tips for others though they might be obvious: (1.) "app.use(awsServerlessExpressMiddleware.eventContext())" must be done before any "app.use('/', index);" that will use the API-Gateway context/event (2.) General info available here github.com/awslabs/aws-serverless-express

Jason · Accepted Answer · 2024-04-19 23:40:57Z

3

With version 4.x (2023-24) of the @codegenie/serverless-express package, you access the API Gateway event context using getCurrentInvoke in your controllers :

const { getCurrentInvoke } = require('@codegenie/serverless-express')
...
const { event, context } = getCurrentInvoke()

Source

edited Apr 19, 2024 at 23:40

Jason

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answered Mar 6, 2024 at 22:10

cooow

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3 Comments

Mridang Agarwalla Over a year ago

I looked into the implementation of the getCurrentInvoke and it seems rather buggy to me. raw.githubusercontent.com/CodeGenieApp/serverless-express/… This doesn't factor in the fact that Lambda will reuse the same instance to serve multiple requests concurrently if you're using Node.js 10.x runtime or later. This pattern does not account for concurrent execution within the same Lambda instance, which could lead to incorrect event and context data being accessed across different invocations.

cooow Over a year ago

Very interesting point @MridangAgarwalla ! Do you have any suggestions to avoid this issue, maybe another way to extract context from event directly ?

gusgorman Over a year ago

for anyone who is concerned about this, apparently it isn't a problem: github.com/CodeGenieApp/serverless-express/issues/674

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