Example binary for wai-handler-hal

Note: This repository is a point-in-time demonstration, reflecting what was current as of June 2026. It is not actively maintained, and hal/wai-handler-hal is no longer considered the obvious default for putting Haskell on Lambda. A rough rule of thumb:

• If your Lambda is obviously a Lambda — a side-effectful function that consumes and returns JSON, invoked as an event handler rather than as an HTTP service — hal (optionally with wai-handler-hal if you also want to expose it behind API Gateway) is still a reasonable, direct fit.
• If your Lambda is really a web service that happens to run on Lambda, prefer building an ordinary Haskell server binary (e.g. warp) and deploying it with the AWS Lambda Web Adapter, either as a container image or as a Lambda Layer. This is cheaper to run behind an HTTP API Gateway, and also opens up Lambda Function URLs and Application Load Balancers as integrations — hal has no JSON mappings for those event/response formats, only for the API Gateway REST API proxy integration shown in this example.

This package shows how to run a Servant API on AWS Lambda. Servant returns a WAI Application, which we wrap with wai-handler-hal and run with hal's 'mRuntime. This allows us to deploy the binary to AWS Lambda, and use it as a Lambda Proxy Integration of an AWS API Gateway REST API (only).

A second executable runs the same WAI Application on the warp web server. This is great for local testing.

Two endpoints are provided:

• GET https://abcde12345.execute-api.us-east-1.amazonaws.com/prod/hoot --- returns { "message": "hoot" }
• GET https://abcde12345.execute-api.us-east-1.amazonaws.com/prod/greet?person=Roy --- returns { "message": "Hello, Roy!" }

Building

Follow the instructions in the wai-handler-hal-cdk subdirectory to build the deployment package and deploy it to AWS using AWS CDK v2.

Hacking

There is a development shell provided. Users on x86_64-linux can run nix develop, and then run npm install from within the wai-handler-hal-cdk subdirectory.

Other Targets

Some people might prefer to deploy OCI Container Images to Elastic Container Registry. There are additional flake outputs showing how to package Lambda binaries into container images:

• packages.x86_64-linux.container is a standard container image built atop Amazon's base image.
• packages.x86_64-linux.tiny-continer is a minimal container image consisting of busybox, Amazon's AWS Lambda Runtime Interface Emulator, and the bootstrap binary.