Kotlin / Gradle

AWS Lambda Function URL and a Micronaut function

Deploy a Micronaut function to AWS Lambda Java 17 runtime and invoke it with a Lambda function URL.

Sergio del Amo

On this guide

In this section

In this guide, we will deploy a Micronaut serverless function to AWS Lambda Java 17 runtime and invoke it with a Lambda function URL.

Getting Started

In this guide, we will create a Micronaut application written in Kotlin.

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=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.

If you use Micronaut Launch, select serverless function as application type and add the aws-lambda and aws-lambda-function-url features.

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

Setup IntelliJ IDEA to develop Micronaut Applications.

Handler

Create a class extending MicronautRequestHandler and define input and output types.

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

package example.micronaut

import io.micronaut.function.aws.MicronautRequestHandler
import java.io.IOException
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 =
        APIGatewayProxyResponseEvent().apply {
            try {
                val json = String(objectMapper.writeValueAsBytes(mapOf("message" to "Hello World")))
                statusCode = 200
                body = json
            } catch (e: IOException) {
                statusCode = 500
            }
        }
}

Handler Test

Write a test that verifies the function behavior:

kotlin/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. As a runtime, select Java 17, Java 21, or Java 25.

Enable function URLs and set Auth Type as NONE.

Upload Code

Create an executable jar including all dependencies:

./gradlew shadowJar

Upload it:

Handler

As Handler, set:

example.micronaut.FunctionRequestHandler

Obtain the Function URL

You can obtain the Function URL in the AWS Console:

aws lambda function url

Invoke it, via a cURL command:

% curl -i https://xxxxxxxx.lambda-url.xxxx.on.aws/
{"message":"Hello World"}

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).