Serverless Haskell

Deploying Haskell code onto AWS Lambda using Serverless.

Requirements

• AWS account
• Stack
• NPM
• Docker

Usage

• Create a Stack package for your code:

  stack new mypackage
  

  LTS 9-12 are supported, older versions are likely to work too but untested.

• Initialise a Serverless project inside the Stack package directory and install the serverless-haskell plugin:

  cd mypackage
  npm init .
  npm install --save serverless serverless-haskell@x.y.z
  

  The version of the NPM package to install must match the version of the Haskell package.

• Create serverless.yml with the following contents:

  service: myservice
  
  provider:
    name: aws
    runtime: nodejs8.10
  
  functions:
    myfunc:
      handler: mypackage.myfunc
      # Here, mypackage is the Haskell package name and myfunc is the executable
      # name as defined in the Cabal file. The handler field may be prefixed
      # with a path of the form `dir1/.../dirn`, relative to `serverless.yml`,
      # which points to the location where the Haskell package `mypackage` is
      # defined. This prefix is not needed when the Stack project is defined at
      # the same level as `serverless.yml`.
  
  plugins:
    - serverless-haskell
  

• Write your main function:

  import qualified Data.Aeson as Aeson
  
  import AWSLambda
  
  main = lambdaMain handler
  
  handler :: Aeson.Value -> IO [Int]
  handler evt = do
    putStrLn "This should go to logs"
    print evt
    pure [1, 2, 3]
  

• Use sls deploy to deploy the executable to AWS Lambda. Note: sls deploy function is not supported yet.

  The serverless-haskell plugin will build the package using Stack and upload it to AWS together with a JavaScript wrapper to pass the input and output from/to AWS Lambda.

  You can test the function and see the invocation results with sls invoke myfunc.

  To invoke the function locally, use sls invoke local -f myfunc.

API Gateway

This plugin supports handling API Gateway requests. Declare the HTTP events normally in serverless.yml and use AWSLambda.Events.APIGateway in the handler to process them.

Serverless Offline can be used for local testing of API Gateway requests.

Notes

• sls deploy function is not supported yet.
• Only AWS Lambda is supported at the moment. Other cloud providers would require different JavaScript wrappers to be implemented.

See AWSLambda for documentation, including additional options to control the deployment.

Testing

• Haskell code is tested with Stack: stack test.
• JavaScript code is linted with eslint.

Integration tests

Integration test verifies that the project can build and deploy a complete function to AWS, and it runs with expected functionality.

Integration test is only automatically run up to deployment due to the need for an AWS account. To run manually:

• Ensure you have the required dependencies: curl, jq, NPM, pwgen and Stack.
• Get an AWS account and add the access credentials into your shell environment.
• Run ./integration-test/run.sh. The exit code indicates success.
• To verify just the packaging, without deployment, run ./integration-test/run.sh --dry-run.
• By default, the integration test is run with LTS 12. To specify a different series, use RESOLVER_SERIES=lts-9.

Releasing

• Run the integration tests.
• Install bumpversion: pip install bumpversion.
• Run bumpversion major|minor|patch.
• Run git push --tags && git push.