Deploy a Micronaut application as a GraalVM Native Image to AWS Lambda

Learn how to distribute a Micronaut Java application built as a GraalVM Native image to AWS Lambda Custom Runtime

Authors: Sergio del Amo

Micronaut Version: 3.2.7

1. Getting Started

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.

The biggest problem with Java applications and Lambda is how to mitigate Cold startups. Executing GraalVM Native images of a Micronaut function in a Lambda Custom runtime is a solution to this problem.

In this guide, we will deploy a Micronaut Application as a GraalVM Native image to an AWS Lambda custom runtime. If your Lambda integrates with API Gateway via a Lambda Proxy, a Micronaut function of type Application with the aws-lambda feature is a good fit, especially when you have multiple endpoints which you wish to delegate to a single Lambda.

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:

  • Some time on your hands

  • A decent text editor or IDE

  • JDK 1.8 or greater installed with JAVA_HOME configured appropriately

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 App

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

mn create-app example.micronaut.complete --features aws-lambda,graalvm
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 use Micronaut Launch, add aws-lambda and graalvm features.

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

4.1. Enable annotation Processing

If you use Java or Kotlin and IntelliJ IDEA, make sure to enable annotation processing.


The generated application contains a BookController. It responds to POST request to /.

package example.micronaut
import io.micronaut.http.annotation.Body
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Post
import java.util.UUID
import javax.validation.Valid

open class BookController {
    open fun save(@Valid @Body book: Book): BookSaved {
        val bookSaved = BookSaved() =
        bookSaved.isbn = UUID.randomUUID().toString()
        return bookSaved
  • The class is defined as a controller with the @Controller annotation mapped to the path /

  • The @Post annotation maps HTTP requests to / to the save method.

  • Add the @Valid annotation to any method parameter that requires validation.

The controller method parameter is a Book object:

package example.micronaut
import io.micronaut.core.annotation.Introspected

class Book {
    var name: String? = null
  • Annotate the class with @Introspected to generate the Bean Metainformation at compile time.

It returns a BookSaved object:

package example.micronaut
import io.micronaut.core.annotation.Introspected

class BookSaved {
    var name: String? = null
    var isbn: String? = null
  • Annotate the class with @Introspected to generate the Bean Metainformation at compile time.

The generated tests illustrates how the code works when the lambda gets invoked:

package example.micronaut;
import com.amazonaws.serverless.proxy.internal.testutils.AwsProxyRequestBuilder
import com.amazonaws.serverless.proxy.internal.testutils.MockLambdaContext
import com.fasterxml.jackson.databind.ObjectMapper
import io.micronaut.http.HttpHeaders
import io.micronaut.http.HttpMethod
import io.micronaut.http.HttpStatus
import io.micronaut.http.MediaType
import org.junit.jupiter.api.Assertions
import org.junit.jupiter.api.Test

class BookRequestHandlerTest {

    fun testBookController() {
        val handler = MicronautLambdaHandler()
        val book = Book() = "Building Microservices"
        val objectMapper = handler.applicationContext.getBean(
        val json = objectMapper.writeValueAsString(book)
        val request = AwsProxyRequestBuilder("/", HttpMethod.POST.toString())
                .header(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON)
        val lambdaContext: Context = MockLambdaContext()
        val response = handler.handleRequest(request, lambdaContext)
        Assertions.assertEquals(response.statusCode, HttpStatus.OK.code)
        val bookSaved: BookSaved = objectMapper.readValue(response.body,
  • 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.

  • You don’t invoke the controller directly. Instead, your handler receives an AWS Proxy Request event which it is routed transparently to your controller.

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 Custom Runtime

create function bootstrap

6.1. Upload Code

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

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

./gradlew buildNativeLambda

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

Once you have a ZIP file, upload it

lambda custom runtime uploadcode

6.2. Handler

As Handler, set:

lambda custom runtime micronaut lambda handler

6.3. Test

You can test it easily. As Event Template use apigateway-aws-proxy to get you started:

test event
  "body": "{\"name\": \"Building Microservices\"}",
  "resource": "/",
  "path": "/",
  "httpMethod": "POST",
  "isBase64Encoded": false,
  "queryStringParameters": {},
  "multiValueQueryStringParameters": {},
  "pathParameters": {},
  "stageVariables": {},

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

Object Computing, Inc. (OCI) sponsored the creation of this Guide. A variety of consulting and support services are available.