Table of Contents

Deploy a Serverless Micronaut function to AWS Lambda Java 17 Runtime

Learn how to distribute a serverless Micronaut function to AWS Lambda 17 Runtime

Authors: Sergio del Amo

Micronaut Version: 4.4.0

Please read about Micronaut AWS Lambda Support to learn more about different Lambda runtime, Triggers, and Handlers, and how to integrate with a Micronaut application.

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

In this guide, we will deploy a Micronaut serverless function to AWS Lambda.

1. Getting Started

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

2. What you will need

To complete this guide, you will need the following:

3. 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.

4. 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
If you don’t specify the --build argument, Gradle 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 feature.

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.

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
    }
}

An included test shows how to verify the function behaviour:

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.

5. Testing the Application

To run the tests:

./gradlew test

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

6. Lambda

Create a Lambda Function. As a runtime, select Java 17.

create function

6.1. Upload Code

Create an executable jar including all dependencies:

./gradlew shadowJar

Upload it:

upload function code

6.2. Handler

As Handler, set:

example.micronaut.FunctionRequestHandler

handler 2

6.3. Test

You can test it easily with a JSON Event:

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

When working with Amazon API Gateway, it’s easy to use apigateway-aws-proxy as an Event Template to get started:

test event

You should see a 200 response:

test result

7. Next steps

Explore more features with Micronaut Guides.

Read more about:

8. Help with the Micronaut Framework

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

9. License

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