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LLRT (LowLatencyRuntime) is a lightweight JavaScript runtime designed to address the growing demand for fast and efficient Serverless applications. LLRT offers up to over10x faster startup and up to2x overall lower cost compared to other JavaScript runtimes running onAWS Lambda

It's built in Rust, utilizing QuickJS as JavaScript engine, ensuring efficient memory usage and swift startup.

_{LLRT -DynamoDB Put, ARM, 128MB:}

_{Node.js 20 -DynamoDB Put, ARM, 128MB:}

HTTP benchmarks measured inround trip time for a cold start (why?)

Download the last LLRT release fromhttps://github.com/awslabs/llrt/releases

ChooseCustom Runtime on Amazon Linux 2023 and package the LLRTbootstrap binary together with your JS code.

ChooseCustom Runtime on Amazon Linux 2023, uploadllrt-lambda-arm64.zip orllrt-lambda-x64.zip as a layer and add to your function

See ourAWS SAM example or:

FROM --platform=arm64 busyboxWORKDIR /var/task/COPY app.mjs ./ADD https://github.com/awslabs/llrt/releases/latest/download/llrt-container-arm64 /usr/bin/llrtRUN chmod +x /usr/bin/llrtENV LAMBDA_HANDLER"app.handler"CMD ["llrt" ]

The followingexample project sets up a lambdainstrumented with a layer containing the llrt runtime.

You can usecdk-lambda-llrt construct library to deploy LLRT Lambda functions with AWS CDK.

import{LlrtFunction}from"cdk-lambda-llrt";consthandler=newLlrtFunction(this,"Handler",{entry:"lambda/index.ts",});

SeeConstruct Hub andits examples for more details.

That's it 🎉

The best way to ensure your code is compatible with LLRT is to write tests and execute them using the built-in test runner. The test runner currently supports Jest/Chai assertions. There are three main types of tests you can create:

Unit Tests

• Useful for validating specific modules and functions in isolation
• Allow focused testing of individual components

End-to-End (E2E) Tests

• Validate overall compatibility with AWS SDK and WinterCG compliance
• Test the integration between all components
• Confirm expected behavior from end-user perspective
• For more information about the E2E Tests and how to run them, seehere.

Web Platform Tests (WPT)

• Useful for validating LLRT’s behavior against standardized browser APIs and runtime expectations
• Ensure compatibility with web standards and cross-runtime environments
• Help verify alignment with WinterCG and broader JavaScript ecosystem
• For setup instructions and how to run WPT in LLRT, seehere.

Test runner uses a lightweight Jest-like API and supports Jest/Chai assertions. For examples on how to implement tests for LLRT see the/tests folder of this repository.

To run tests, execute thellrt test command. LLRT scans the current directory and sub-directories for files that ends with*.test.js or*.test.mjs. You can also provide a specific test directory to scan by using thellrt test -d <directory> option.

The test runner also has support for filters. Using filters is as simple as adding additional command line arguments, i.e:llrt test crypto will only run tests that match the filename containingcrypto.

⚠️ = partially supported in LLRT
⏱ = planned partial support
* = Not native
** = Use fetch instead

Since LLRT is meant for performance critical application it's not recommended to deploynode_modules without bundling, minification and tree-shaking.

LLRT can work with any bundler of your choice. Below are some configurations for popular bundlers:

esbuild index.js --platform=browser --target=es2023 --format=esm --bundle --minify --external:@aws-sdk --external:@smithy

importresolvefrom"@rollup/plugin-node-resolve";importcommonjsfrom"@rollup/plugin-commonjs";importterserfrom"@rollup/plugin-terser";exportdefault{input:"index.js",output:{file:"dist/bundle.js",format:"esm",sourcemap:true,target:"es2023",},plugins:[resolve(),commonjs(),terser()],external:["@aws-sdk","@smithy"],};

importTerserPluginfrom"terser-webpack-plugin";importnodeExternalsfrom"webpack-node-externals";exportdefault{entry:"./index.js",output:{path:"dist",filename:"bundle.js",libraryTarget:"module",},target:"web",mode:"production",resolve:{extensions:[".js"],},externals:[nodeExternals(),"@aws-sdk","@smithy"],optimization:{minimize:true,minimizer:[newTerserPlugin({terserOptions:{ecma:2023,},}),],},};

LLRT includes many AWS SDK clients and utils as part of the runtime, built into the executable. These SDK Clients have been specifically fine-tuned to offer best performance while not compromising on compatibility. LLRT replaces some JavaScript dependencies used by the AWS SDK by native ones such as Hash calculations and XML parsing.V3 SDK packages not included in the list below have to be bundled with your source code. For an example on how to use a non-included SDK, seethis example build script (buildExternalSdkFunction)

LLRT supports the following three bundles by default. Bundle types and suffixes are as follows.

The relationship between the supported packages for each bundle type is as follows.

constresponse=awaitclient.send(command);// or 'transformToByteArray()'conststr=awaitresponse.Body.transformToString();

Same principle as dependencies applies when using TypeScript. TypeScript must be bundled and transpiled into ES2023 JavaScript.

What justifies the introduction of another JavaScript runtime in light of existing options such asNode.js,Bun &Deno?

Node.js, Bun, and Deno represent highly proficient JavaScript runtimes. However, they are designed with general-purpose applications in mind. These runtimes were not specifically tailored for the demands of a Serverless environment, characterized by short-lived runtime instances. They each depend on a (Just-In-Time compiler (JIT) for dynamic code compilation and optimization during execution. While JIT compilation offers substantial long-term performance advantages, it carries a computational and memory overhead.

In contrast, LLRT distinguishes itself by not incorporating a JIT compiler, a strategic decision that yields two significant advantages:

A) JIT compilation is a notably sophisticated technological component, introducing increased system complexity and contributing substantially to the runtime's overall size.

B) Without the JIT overhead, LLRT conserves both CPU and memory resources that can be more efficiently allocated to code execution tasks, thereby reducing application startup times.

There are many cases where LLRT shows notable performance drawbacks compared with JIT-powered runtimes, such as large data processing, Monte Carlo simulations or performing tasks with hundreds of thousands or millions of iterations. LLRT is most effective when applied to smaller Serverless functions dedicated to tasks such as data transformation, real time processing, AWS service integrations, authorization, validation etc. It is designed to complement existing components rather than serve as a comprehensive replacement for everything. Notably, given its supported APIs are based on Node.js specification, transitioning back to alternative solutions requires minimal code adjustments.

1. Clone code and cd to directory

git clone git@github.com:awslabs/llrt.gitcd llrt

2. Install git submodules

git submodule update --init --checkout

3. Install rust

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | bash -s -- -ysource "$HOME/.cargo/env"

4. Install dependencies

# MacOSbrew install zig make cmake zstd node corepack# Ubuntusudo apt -y install make zstdsudo snap install zig --classic --beta# Windows WSL2 (requires systemd to be enabled*)sudo apt -y install cmake g++ gcc make zip zstdsudo snap install zig --classic --beta# Windows WSL2 (If Node.js is not yet installed)sudo curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/master/install.sh | bashnvm install --lts

* SeeMicrosoft Devblogs

5. Install Node.js packages

corepack enableyarn

6. Install generate libs and setup rust targets & toolchains

make stdlib && make libs

7. Build binaries for Lambda (Per bundle type and architecture desired)

# for arm64, usemake llrt-lambda-arm64.zipmake llrt-lambda-arm64-no-sdk.zipmake llrt-lambda-arm64-full-sdk.zip# or for x86-64, usemake llrt-lambda-x64.zipmake llrt-lambda-x64-no-sdk.zipmake llrt-lambda-x64-full-sdk.zip

8. Build binaries for Container (Per bundle type and architecture desired)

# for arm64, usemake llrt-container-arm64make llrt-container-arm64-no-sdkmake llrt-container-arm64-full-sdk# or for x86-64, usemake llrt-container-x64make llrt-container-x64-no-sdkmake llrt-container-x64-full-sdk

9. Optionally build for your local machine (Mac or Linux)

make releasemake release-no-sdkmake release-full-sdk

You should now have allrt-lambda-arm64*.zip orllrt-lambda-x64*.zip. You can manually upload this as a Lambda layer or use it via your Infrastructure-as-code pipeline

Please note that in order to run the example you will need:

• Valid AWS credentials via a~/.aws/credentials or via environment variables.

export AWS_ACCESS_KEY_ID=XXXexport AWS_SECRET_ACCESS_KEY=YYYexport AWS_REGION=us-east-1

• A DynamoDB table (withid as the partition key) onus-east-1
• Thedynamodb:PutItem IAM permission on this table. You can use this policy (don't forget to modify <YOUR_ACCOUNT_ID>):

{"Version":"2012-10-17","Statement": [    {"Sid":"putItem","Effect":"Allow","Action":"dynamodb:PutItem","Resource":"arn:aws:dynamodb:us-east-1:<YOUR_ACCOUNT_ID>:table/quickjs-table"    }  ]}

Start thelambda-server.js in a separate terminal

node lambda-server.js

Then run llrt:

make run

Load extra certificate authorities from a PEM encoded file

Set a memory threshold in MB for garbage collection. Default threshold is 20MB

Extends the HTTP request version. By default, only HTTP/1.1 is enabled. Specifying '2' will enable HTTP/1.1 and HTTP/2.

Filter the log output by target module, level, or both (using=). Log levels are case-insensitive and will also enable any higher priority logs.

Log levels in descending priority order:

• Error
• Warn | Warning
• Info
• Debug
• Trace

Example filters:

• warn will enable all warning and error logs
• llrt_core::vm=trace will enable all logs in thellrt_core::vm module
• warn,llrt_core::vm=trace will enable all logs in thellrt_core::vm module and all warning and error logs in other modules

Space-delimited list of hosts or socket paths which should be allowed for network connections. Network connections will be denied for any host or socket path missing from this list. Set an empty list to deny all connections

Space-delimited list of hosts or socket paths which should be denied for network connections

Set a timeout in seconds for idle sockets being kept-alive. Default timeout is 15 seconds

Used to explicitly specify a preferred platform for the Node.js package resolver. The default isbrowser. Ifnode is specified, "node" takes precedence in the search path. If a value other thanbrowser ornode is specified, it will behave as if "browser" was specified.

Set the TLS version to be used for network connections. By default only TLS 1.2 is enabled. TLS 1.3 can also be enabled by setting this variable to1.3

Although Init Durationreported by Lambda is commonly used to understand cold start impact on overall request latency, this metric does not include the time needed to copy code into the Lambda sandbox.

The technical definition of Init Duration (source):

For the first request served, the amount of time it took the runtime to load the function and run code outside of the handler method.

Measuring round-trip request duration provides a more complete picture of user facing cold-start latency.

Lambda invocation results (λ-labeled row) report the sum total of Init Duration + Function Duration.

SeeCONTRIBUTING for more information.

This library is licensed under the Apache-2.0 License. See theLICENSE file.