Kotlin / Gradle

Deploy a Micronaut function as a GraalVM Native Executable to AWS Lambda

Learn how to distribute a Micronaut function built as a GraalVM native executable to an AWS Lambda custom runtime

Sergio del Amo

On this guide

In this section

Introduction

Please read about Micronaut AWS Lambda Support to learn more about different Lambda runtimes, triggers, and handlers, and how to integrate them with a Micronaut application.

The biggest problem with Java applications and Lambda is how to mitigate cold startups. Executing GraalVM native executables of a Micronaut function in a Lambda custom runtime is a solution to this problem.

If you want to respond to triggers such as queue events, S3 events, or single endpoints, you should code your Micronaut functions as serverless functions.

Getting Started

In this guide, we will deploy a Micronaut function written in Kotlin as a GraalVM native executable to an AWS Lambda custom runtime.

What you will need

To complete this guide, you will need the following:

Some time on your hands
A decent text editor or IDE (e.g. IntelliJ IDEA)
JDK 21 or greater installed with JAVA_HOME configured appropriately

Solution

We recommend that you follow the instructions in the next sections and create the application step by step. However, you can go right to the completed example.

Download and unzip the source

Writing the Application

Create an application using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-function-app example.micronaut.micronautguide --features=graalvm,aws-lambda --build=gradle --lang=kotlin

Note	If you don’t specify the `--build` argument, Gradle with the Kotlin DSL is used as the build tool. If you don’t specify the `--lang` argument, Java is used as the language. If you don’t specify the `--test` argument, JUnit is used for Java and Kotlin, and Spock is used for Groovy.

The previous command creates a Micronaut application with the default package example.micronaut in a directory named micronautguide.

Note	If you use Micronaut Launch, select `Serverless function` as application type and add the `graalvm` and `aws-lambda` features.

Setup IntelliJ IDEA to develop Micronaut Applications.

Code

The generated project contains sample code. Let’s explore it.

The application contains a class extending MicronautRequestHandler

src/main/kotlin/example/micronaut/FunctionRequestHandler.kt

package example.micronaut

import io.micronaut.function.aws.MicronautRequestHandler
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import io.micronaut.json.JsonMapper;
import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent
import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyResponseEvent
import jakarta.inject.Inject
class FunctionRequestHandler : MicronautRequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent>() {
    @Inject
    lateinit var objectMapper: JsonMapper

    override fun execute(input: APIGatewayProxyRequestEvent): APIGatewayProxyResponseEvent {
        val response = APIGatewayProxyResponseEvent()
        try {
            val json = String(objectMapper.writeValueAsBytes(mapOf("message" to "Hello World")))
            response.statusCode = 200
            response.body = json
        } catch (e: IOException) {
            response.statusCode = 500
        }
        return response
    }
}

The class extends MicronautRequestHandler and defines input and output types.

The generated test shows how to verify the function behavior:

src/test/kotlin/example/micronaut/FunctionRequestHandlerTest.kt

package example.micronaut

import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent
import org.junit.jupiter.api.Assertions.assertEquals
import org.junit.jupiter.api.Test

class FunctionRequestHandlerTest {

    @Test
    fun testHandler() {
        val handler = FunctionRequestHandler()
        val request = APIGatewayProxyRequestEvent()
        request.httpMethod = "GET"
        request.path = "/"
        val response = handler.execute(request)
        assertEquals(200, response.statusCode.toInt())
        assertEquals("{\"message\":\"Hello World\"}", response.body)
        handler.close()
    }
}

When you instantiate the Handler, the application context starts.
Remember to close your application context when you end your test. You can use your handler to obtain it.
Invoke the execute method of the handler.

Testing the Application

To run the tests:

./gradlew test

Then open build/reports/tests/test/index.html in a browser to see the results.

Lambda

Create a Lambda function. For the runtime, select Custom Runtime. Select the x86_64 or arm64 architecture to match the computer you use to build the GraalVM Native Image.

The Micronaut framework eases the deployment of your functions as a Custom AWS Lambda runtime.

The main API you interact with is AbstractMicronautLambdaRuntime. This abstract class can be subclassed to create your custom runtime mainClass. That class includes the code to perform the Processing Tasks described in the Custom Runtime documentation.

Upload Code

The generated project contains such a class:

Note	Missing source `FunctionLambdaRuntime`.

./gradlew buildNativeLambda

The above command generates a ZIP file which contains a GraalVM Native Executable of the application, and a bootstrap file which executes the native executable. The GraalVM Native Executable of the application is generated inside a Docker container.

Once you have a ZIP file, upload it.

Handler

The handler used is the one created at FunctionLambdaRuntime.

Thus, you don’t need to specify the handler in the AWS Lambda console.

However, you can specify it in the console as well:

example.micronaut.FunctionRequestHandler

lambda custom runtime functionrequest handler

Test

You can test it easily.

{
  "path": "/",
  "httpMethod": "GET",
  "headers": {
    "Accept": "application/json"
  }
}

You should see a 200 response:

aws lambda function graalvm warm startup

Next Steps

Explore more features with Micronaut Guides.

Help with the Micronaut Framework

The Micronaut Foundation sponsored the creation of this Guide. A variety of consulting and support services are available.

License

Note	All guides are released with an Apache License 2.0 for the code and a Creative Commons Attribution 4.0 license for the writing and media (images).