JarCastingScala Servers for Lambda
Scala Servers for Lambda allows you to run existing Scala servers over API Gateway and AWS Lambda.
Benefits:
- Define logic once, and use it in both a server and serverless environment.
- Simpler testing, as the logic has been isolated from Lambda completely.
- No need to deal with Lambda's API directly, which aren't easy to use from Scala.
- All code is deployed to single Lambda function, meaning our functions will be kept warm more often.
How to import the library
Choose one of the following dependencies and add it to your SBT file.
Please make sure to use the latest available version which should be visible in the badge at the top of the repo.
// For use with http4s and cats effect
libraryDependencies += "com.dvdkly" %% "scala-server-lambda-http4s" % "<version>"
// For use with http4s and ZIO
libraryDependencies += "com.dvdkly" %% "scala-server-lambda-http4s-zio" % "<version>"
// For use with akka-http
libraryDependencies += "com.dvdkly" %% "scala-server-lambda-akka-http" % "<version>"
Dependencies
Having a large JAR can increase cold start times, so dependencies have been kept to a minimum. All servers depend on circe. Additionally:
- http4s depends on
http4s-core. - akka-http depends on
akka-httpandakka-stream.
Neither of these depend on the AWS SDK at all, which substantially reduces the size.
Getting Started
More thorough examples can be found in the examples directory.
http4s
First, add the dependency:
libraryDependencies += "com.dvdkly" %% "scala-server-lambda-http4s" % "0.5.1"
Next, we define a simple HttpService. Then, we simply need to define a new class for Lambda.
object Route {
// Set up the route
val service: HttpService[IO] = HttpService[IO] {
case GET -> Root / "hello" / name => Ok(s"Hello, $name!")
}
// Define the entry point for Lambda
class EntryPoint extends Http4sLambdaHandler(service)
}
Thats it! Make sure any dependencies are initialized in the Route object so they are computed only once.
akka-http
First, add the dependency:
libraryDependencies += "com.dvdkly" %% "scala-server-lambda-akka-http" % "0.5.1"
Next, we define a simple Route. Then, we simply need to define a new class for Lambda.
object Route {
// Set up the route
val route: Route =
path("hello" / Segment) { name: String =>
get {
complete(s"Hello, $name!")
}
}
// Set up dependencies
implicit val system: ActorSystem = ActorSystem("example")
implicit val materializer: ActorMaterializer = ActorMaterializer()
implicit val ec = scala.concurrent.ExecutionContext.Implicits.global
// Define the entry point for Lambda
class EntryPoint extends AkkaHttpLambdaHandler(route)
}
Thats it! Make sure any dependencies are initialized in the Route object so they are computed only once.
Deploying to AWS
To deploy to Lambda, we need to create a jar with all of our dependencies. The easiest way to do this is using sbt-assembly.
Once we have the jar, all we need to do is upload it to Lambda. The preferred way to do this is using the serverless framework which greatly simplifies this (and is what is used in the examples), but there is no issues with doing it manually.
When deploying to Lambda, the handler should be specified as <PACKAGE_NAME>.Route$EntryPoint::handle (if you followed the example above).
Finally, an API can be created in API Gateway. Lambda Proxy integration must be enabled.