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awslabs/llrt

★ 8,737RustAudience · developerComplexity · 3/5Setup · moderate

TLDR

LLRT is an experimental AWS JavaScript runtime for Lambda functions that starts up to 10x faster and costs up to 2x less than Node.js by using a lightweight Rust-based engine instead.

Mindmap

mindmap
  root((LLRT))
    What it does
      Faster Lambda cold start
      Lower billing cost
      JS on serverless
    Tech Stack
      Rust runtime
      QuickJS engine
      AWS Lambda
    Deployment
      Lambda layer
      Custom runtime
      Container image
      AWS SAM and CDK
    Limitations
      Partial Node.js API
      Experimental only
    Audience
      Serverless developers
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Things people build with this

USE CASE 1

Replace Node.js as the runtime for your AWS Lambda JavaScript functions to cut cold-start times and reduce billing.

USE CASE 2

Evaluate whether your existing serverless JavaScript code is compatible with LLRT's Node.js API subset before migrating.

USE CASE 3

Deploy LLRT as a Lambda layer or custom runtime and benchmark startup speed against your current setup.

USE CASE 4

Run LLRT's built-in test runner locally to validate your JavaScript code before deploying to Lambda.

Tech stack

RustJavaScriptQuickJSAWS Lambda

Getting it running

Difficulty · moderate Time to first run · 1h+

Requires an AWS account and familiarity with Lambda deployment, code may need changes as LLRT is not a drop-in Node.js replacement.

No license information is mentioned in the explanation.

In plain English

LLRT, which stands for Low Latency Runtime, is an experimental JavaScript runtime built by AWS Labs and designed specifically for serverless functions running on AWS Lambda. A runtime is the environment that executes your code. Most Lambda functions that run JavaScript use Node.js as their runtime, but Node.js was built for general-purpose server use and carries more weight than a short-lived serverless function needs. LLRT aims to be a smaller, faster alternative built from the ground up for this narrow use case. The project claims up to 10 times faster startup speed and up to 2 times lower cost compared to Node.js running on AWS Lambda. The speed difference comes from how the runtime starts: Lambda functions go through a cold start whenever a new copy is spun up, and a lighter runtime reaches ready state faster. Cost savings follow from the reduced time billed during those starts. LLRT is built in Rust, a systems programming language known for efficient memory handling. It uses an embedded JavaScript engine called QuickJS to actually interpret and run JavaScript code. The result is a much smaller binary than a full Node.js install, which is what makes the startup advantage possible. An important caveat throughout the README: LLRT is not a drop-in replacement for Node.js. It only supports a portion of the standard Node.js APIs, and several commonly used modules like http, https, and SQLite are not supported or only partially supported. Code that works on Node.js may need changes before it runs on LLRT. The README includes a compatibility table listing which Node.js modules are supported, partially supported, or unavailable. Deployment options include packaging LLRT as a custom runtime, using it as a Lambda layer, bundling it into a container image, or using it via AWS SAM or AWS CDK tooling. There is also a built-in test runner for checking that your code works with LLRT before deploying. The project is explicitly marked as experimental and intended for evaluation rather than production use. The full README is longer than what was shown.

Copy-paste prompts

Prompt 1
How do I deploy an existing Node.js Lambda function to use the LLRT runtime as a Lambda layer? Walk me through the steps using AWS SAM.
Prompt 2
My Lambda function uses the https module which LLRT does not support. What are my options for making it work with awslabs/llrt?
Prompt 3
Write a simple AWS Lambda function in JavaScript that is compatible with awslabs/llrt, handles an API Gateway event, and returns a JSON response.
Prompt 4
How do I use the awslabs/llrt built-in test runner to check if my JavaScript code will work before deploying to Lambda?
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