Rust-based WebAssembly (wasm) module as a Lambda Layer

This repo showcases how we can call wasm from Lambda layer

Why we need this?

• By using Rust-based WebAssembly (wasm), we can access its power while keeping the functions accessible from TypeScript.
• Additionally, we can avoid including the wasm files in Lambda, which reduces the size and makes it reusable.

Prerequisite

install wasm-pack to build wasm file from rust

cargo install wasm-pack

How to use

1. Set your development Stack account

• create .env file and add your setup

ACCOUNT_NAME=xxx

2. Build wasm

• Compile wasm from Rust. In this example, we build wasm-add module into wasm file.

make build_wasm moduleName=wasm-add

3. Install files

This will link local dependencies as well

yarn install

4. Deploy

• Then call deploy

yarn cdk:deploy --profile={your profile}

Accessing Lambda layer

• CDK's NodejsFunction uses esbuild under the hood, hence all js files in Lambda layer will be bundled into one index.js file
• This approach does not work with wasm since internally a wasm-js tries to access wasm in the same directory which is /var/task on Lambda.

const path = require('path').join(__dirname, 'wasm_add_bg.wasm'); // path is `/var/task/wasm_add_bg.wasm`
const bytes = require('fs').readFileSync(path); // The file doesn't exist!

const wasmModule = new WebAssembly.Module(bytes);

• In order to call wasm from our Lambda, we deploy our wasm Lambda layer under opt/nodejs/node_modules (NODE_PATH)
• To do so, we copy all files under layer/wasm-add/nodejs/node_modules after wasm-pack build
  • This has another benefit; We don't have to add /opt/xxx in tsconfig's paths because layer/wasm-add is accessible as a workspace from Lambda functions
• When we deploy, path should be layers/{moduleName} so that the same directory structure will be kept on Lambda layer

this.layer = new Lambda.LayerVersion(this, "Layer", {
  code: Lambda.Code.fromAsset(
    path.join(`${__dirname}/..`, "layers/wasm-add"),
  ),
  compatibleRuntimes: [Lambda.Runtime.NODEJS_16_X],
  description: "A layer with wasm",
});

• The Lambda function access wasm-add like this

import { add } from "wasm-add"; // we don't use `/opt/nodejs/wasm-add`!

export const handler = {...};

Reference

• A tutorial for Rust wasm https://developer.mozilla.org/en-US/docs/WebAssembly/Rust_to_wasm#rust_and_webassembly_use_cases
• Rust wasm https://rustwasm.github.io/wasm-bindgen/examples/add.html
• Great explanation about not including the code from Lambda Layer in Lambda function https://www.shawntorsitano.com/2022/06/19/creating-lambda-layers-with-typescript-and-cdk-the-right-way/