aws-lambda4s, The Easiest Way to Build Lambdas With Scala

March 26, 2018

Lately, I’ve been writing a lot of serverless functions using AWS Lamba and Scala (my favorite “workhorse” language these days). Not having to worry about managing server instances has been a huge boon to my productivity, however like most AWS services, Lambda takes a fair amount of boilerplate to setup in a way that’s “production ready”.

Namely, these are the things I wanted:

  • An API that lets me use Scala’s case classes and convert them to/from JSON (which Lambda expects)
  • Logging, println is not “logging”
  • An easy way to write Lambdas that use API Gateway via Proxy integration
  • Dead simple HTTP route matching for building a REST API

Googling around, I didn’t find anything that fit what I wanted, so I ended up writing my own micro library to do all of this and make writing Lambdas in Scala super easy, it’s called aws-lambda4s. It’s open source on Github. Let me tell you just how easy it is to use.

Writing a Scala Lambda Is Just A Few Lines Of Code

import lambda4s._

/** aws-lambda4s supports automatic serialization of
these case classes to/from JSON */
case class InputItem(sku: String)
case class OutputItem(name: String, price: Double)

class MyLambda extends LambdaFunction[InputItem, OutputItem] {
    override def handle(input: InputItem, context: Context): OutputItem = {"yay, logging!") // logging is already set up for you
        OutputItem(, product.price)

Writing a REST API using Lambda Is Just as easy

import lambda4s._

// pretend Users are a domain object that lives in a database
case class User(id: String, name: String)

class MyAPI extends LambdaProxyFunction {
    override def handle(request: Request, context: Context): Response = {
       // easy API route matching built right in
       // no crazy syntax, just normal Scala pattern matching
        request match {
            case Get("users", userId) =>
              val user = someDatabase.findById(userId)
              Response(body = JSON.toJSON(user))

            case Post("users") =>
              val user = JSON.fromJSON[User](request.body)
              Response(statusCode = 200, body = """{"status": "success"}""")


That’s it. You can find aws-lambda4s on Github and I have a full working example using aws-lambda4s that’s deployable with a single command here.

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