hal
A runtime environment for Haskell applications running on AWS Lambda.
Flexible
This library uniquely supports different types of AWS Lambda Handlers for your needs/comfort with advanced Haskell. Instead of exposing a single function that constructs a Lambda, this library exposes many.
For lambdas that are pure and safe, then pureRuntime
is ideal.
It accepts a handler with the signature (FromJSON a, ToJSON b) => a -> b
.
This runtime guarantees that side-effects cannot occur.
For advanced use cases mRuntime
unlocks the full power of Monad Transformers.
It accepts handlers with the signature (MonadCatch m, MonadIO m, FromJSON event, ToJSON result) => (event -> m result)
This enables users to add caching logic or expose complex environments.
With numerous options in between these two, developers can choose the right balance of flexibility vs simplicity.
Performant
Measuring lambda performance is tricky, so investigation and optimization is ongoing. Current indications show a warm execution overhead of only ~20% more than the official Rust Runtime (a much lower level language).
Robust
While testing continues, we have executed over 30k test events without error caused by the runtime. Naive approaches lead to error rates well over 10%.
Table of Contents
Supported Platforms / GHC Versions
We currently support this library under the same environment that AWS Lambda supports.
Our CI currently targets the latest three LTS Stackage Versions,
the latest three minor versions of GHC under Cabal
(e.g. 8.6.x
, 8.4.x
, and 8.2.x
), and GHC-head / Stackage nightly builds.
If you haven't already, adding docker: { enable: true }
to your stack.yaml
file will ensure that you're building a binary that can run in
AWS Lambda.
Quick Start
This quick start assumes you have the following tools installed:
Add hal
to your stack.yaml's extra-deps
and enable
Docker integration so that your binary is automatically compiled in a
compatible environment for AWS. Also add hal
to your project's
dependency list (either project-name.cabal
or package.yaml
)
#...
extra-deps:
- hal-${DESIRED_VERSION}
# ...
docker:
enable: true
# ...
Then, define your types and handler:
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE NamedFieldPuns #-}
module Main where
import AWS.Lambda.Runtime (pureRuntime)
import Data.Aeson (FromJSON, ToJSON)
import GHC.Generics (Generic)
data IdEvent = IdEvent { input :: String } deriving Generic
instance FromJSON IdEvent
data IdResult = IdResult { output :: String } deriving Generic
instance ToJSON IdResult
handler :: IdEvent -> IdResult
handler IdEvent { input } = IdResult { output = input }
main :: IO ()
main = pureRuntime handler
Your binary should be called bootstrap
in order for the custom runtime
to execute properly:
# Example snippet of package.yaml
# ...
executables:
bootstrap:
source-dirs: src
main: Main.hs # e.g. {project root}/src/Main.hs
# ...
You'll need to either build on a compatible linux host or inside a compatible docker container (or some other mechanism like nix). Note that current Stack LTS images are not compatible. If you see an error message that contains "version 'GLIBC_X.XX' not found" when running (hosted or locally), then your build environment is not compatible.
Enable stack's docker integration and define an optional image within stack.yaml:
# file: stack.yaml
docker:
enabled: true
# If omitted, this defaults to fpco/stack-build:lts-${YOUR_LTS_VERSION}
image: ${BUILD_IMAGE}
Don't forget to define your CloudFormation stack:
# file: template.yaml
AWSTemplateFormatVersion: '2010-09-09'
Transform: 'AWS::Serverless-2016-10-31'
Description: Test for the Haskell Runtime.
Resources:
HelloWorldApp:
Type: 'AWS::Serverless::Function'
Properties:
Handler: NOT_USED
Runtime: provided
# CodeUri is a relative path from the directory that this CloudFormation
# file is defined.
CodeUri: .stack-work/docker/_home/.local/bin/
Description: My Haskell runtime.
MemorySize: 128
Timeout: 3
Finally, build, upload and test your lambda!
# Build the binary, make sure your executable is named `bootstrap`
stack build --copy-bins
# Create your function package
aws cloudformation package \
--template-file template.yaml \
--s3-bucket your-existing-bucket > \
deployment_stack.yaml
# Deploy your function
aws cloudformation deploy \
--stack-name "hello-world-haskell" \
--region us-west-2 \
--capabilities CAPABILITY_IAM \
--template-file deployment_stack.yaml
# Take it for a spin!
aws lambda invoke \
--function-name your-function-name \
--region us-west-2 \
--payload '{"input": "foo"}' \
output.txt
Local Testing
Dependencies
Build
docker pull fpco/stack-build:lts-{version} # First build only, find the latest version in stack.yaml
stack build --copy-bins
Execute w/ Docker
echo '{ "accountId": "byebye" }' | docker run -i --rm \
-e DOCKER_LAMBDA_USE_STDIN=1 \
-v ${PWD}/.stack-work/docker/_home/.local/bin/:/var/task \
lambci/lambda:provided
Execute w/ SAM Local
Note that hal currently only supports aws-sam-cli on versions <1.0.
echo '{ "accountId": "byebye" }' | sam local invoke --region us-east-1