70: Haskell Serverless

Finally Ready to Go

• We’ve got our environment all set up so let’s get going!

• Steps

  • A new stack project using the template
  • stack new my-haskell-lambda https://github.com/theam/aws-lambda-haskell-runtime/raw/master/stack-template.hsfiles --resolver=lts-12.13 --omit-packages
  • Say it with me “stack is not like NPM, it is NOT a package manager” stack handles the management of your tool-chain.
  • resolver ?

  Specifies which snapshot is to be used for this project. A snapshot defines a GHC version, a number of packages available for installation, and various settings like build flags. It is called a resolver since a snapshot states how dependencies are resolved. There are currently four resolver types:

• omit-packages ? this leaves the extra-depsflag commented out in the stack.yml
• Added to stack.yml

packages:
- .

extra-deps:
- aws-lambda-haskell-runtime-1.0.9

• initially I had only added the extra-deps. I didn’t realize that having added --omit-packages I still needed to add packages .
• running make and we’re off to the races Progress 0/111

aws lambda create-function --function-name lambda-haskell \
--zip-file fileb://build/function.zip --handler src/Lib.handler \
--layers arn:aws:lambda:us-west-2:785355572843:layer:haskell-runtime:2 \
--runtime provided --role arn:aws:iam::XXXXXXXXXX:role/lambda-haskell-role

• Oh man. needed
• Success it’s been deployed.
• Let’s see if it works on the first try…
• NOPE execute failure. :cry:
• Oh well, we spelled the handler wrong. AND
• we had the wrong ‘Layer ARN’ This is the custom runtime, once we updated it to match the read me file, we had
• :rocket: Lift Off!!

Can we update the code ?

aws lambda update-function-code --zip-file fileb://build/function.zip --publish --function-name lambda-haskell

HELL YES we can.

OK. So what did we actually deploy ? Let’s walk through the code.

• Lib source file with aws runtime for having access to the ‘Context’ that is passed in to our application when it’s instantiated.

• GHC.Generics for work with JSON

• Aeson for (de)serializing JSON to our types

• Handler

  • This is defined in scr/Lib
  • Must be called handler limit of Haskell runtime
  • handler :: Person -> Context -> IO (Either String Person)

• Main

  • import aws runtime again
  • import fully qualified Lib
  • call configureLambda which will dynamically generate our dispatchers for us.
  • also of note, with compared to C++ and Rust runtimes, Haskell doesn’t need the entire runtime included with it. I am guessing it can make smart decisions about what is required
  • we can create more ‘handlers’ just need to remember to import them

BOOM

Person API *update age to a negative value or 0 and see the string response. Thanks great!

{
 "personAge": 43,
 "personName": "John Doe"
}

Picks

Resources

Runtime Details with Haskell Medium Post

Custom Haskell Runtime Repo

Lexi Lambda Guide to Haskell 2018

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