/aws-lambda-custom-runtime

Primary LanguageJavaScriptMIT LicenseMIT

What is this?

If you're not happy with the runtimes already provided out of the box by AWS, you can create your own custom runtime and put it in a Lambda Layer, making it shareable across severals Lambdas.

This project serves as a reference example of how to setup a custom AWS Lambda runtime as a Lambda Layer with CDK using TypeScript.

In the example we will be using nodejs v16 as the runtime.

How to run

Requirements

You need to have

  • an AWS account
  • a default AWS profile (aws configure) with sufficient rights to create resources
  • Docker installed on your machine

Steps

  1. Go to cdk/bin/custom-runtime-cdk-app.ts and add your account and region.
  2. npm run build
  3. npm run deploy
  4. Invoke the lambda function (e.g. through the AWS console) and it will return
{
  "statusCode": 200,
  "nodeVersion": "v16.14.2"
}

You might need to run cdk bootstrap if step 3 fails.

How it works

An older post from Amazon walks you through the process, but in summary you have to create an executable file named bootstrap that the AWS Lambda environment will execute when the function is invoked.

bootstrap must meet the requirements specified by the AWS Lambda runtime API, and will execute the lambda handler specified in the CDK in the context of what itself runs in, in our case node16.

In this example I'm using Docker to create a Lambda Layer containing the custom runtime. The custom-runtime/Dockerfile contains the details, but in essence we grab the node executable from nodejs.org, put it in a bin folder and then zip it along with a bootstrap, and copy the resulting zip-file to the Docker host (i.e. your machine).

The content of the zip-file looks like this:

├─📂 bin
│ └─📜 node
└─📜 bootstrap

The zip-file is referenced in the cdk stack definition, and used to create a layer that a Lambda can use.

The bootstrap-file in this example is taken from LambCI and implements the Lambda runtime API in javascript. I have only added a shebang.

You could rename bootstrap to bootstrap.js (remove the shebang) and then create a bootstrap with the following

#!/bin/sh

set -e

while true
do
    /opt/bin/node "/opt/bootstrap.js" 2>&1
done

The layer is put in the opt directory by AWS, so we need to include that.