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

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

Authors: Sergio del Amo

Micronaut Version: 2.0.1

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 are going to deploy a Micronaut Application as a GraalVM Native image to a 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. Specially, when you have multiple endpoints which you wish to delegate to a single Lambda.

1.1 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

You will need also an AWS Account.

1.2 Solution

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


Then, cd into the complete folder which you will find in the root project of the downloaded/cloned project.

2 Writing the App

Create a Micronaut application with the aws-lambda and graalvm features using the CLI:

% mn create-app example.micronaut.complete --lang=kotlin --features aws-lambda,graalvm

2.1 Code

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

@Controller (1)
open class BookController {
    @Post (2)
    open fun save(@Valid @Body book: Book): BookSaved { (3)
        val bookSaved = BookSaved() =
        bookSaved.isbn = UUID.randomUUID().toString()
        return bookSaved
1 The class is defined as a controller with the @Controller annotation mapped to the path /
2 The @Post annotation is used to map HTTP request to / to the the save method.
3 Add the @Valid annotation to any method parameter’s object which requires validation.

The controller’s method parameter is a Book object:

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

@Introspected (1)
class Book {
    var name: String? = null
1 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

@Introspected (1)
class BookSaved {
    var name: String? = null
    var isbn: String? = null
1 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() (1)
        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) (2)
        Assertions.assertEquals(response.statusCode, HttpStatus.OK.code)
        val bookSaved: BookSaved = objectMapper.readValue(response.body,
        handler.applicationContext.close() (3)
1 When you instantiate the Handler, the application context starts.
2 Remember to close your application context when you end your test. You can use your handler to obtain it.
3 You don’t invoke the controller directly. Instead, your handler receives a AWS Proxy Request event which it is routed transparently to your controller.

3 Lambda

3.1 Create Function

Create a Lambda Function. As a runtime, select Custom Runtime

create function

3.2 Upload Code

Micronaut’s eases the deployment of your functions as a Custom AWS Lambda runtime.

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


We deploy our custom runtime code as a ZIP file. At the root of the ZIP file you need a bootstrap file.

If there’s a file named bootstrap in your deployment package, Lambda executes that file.

The generated application contains a bootstrap bash script:

set -euo pipefail
./complete -Xmx128m -Djava.library.path=$(pwd)

To generate a GraalVM Native image of the application, we need a file.

Args = -H:Name=complete \
  • The H:Class argument defines the main class of your app.

  • The H:Name argument defines the native image name. The Dockerfile references this name.


The project includes a Dockerfile to generate a GraalVM Native image.

  • Uses the amazonlinux image

  • Builds the JAR of the function.

  • Install the necessary dependencies.

  • Downloads GraalVM community edition

  • Installs native-image utility.

  • With the native-image command and the JAR, generates a GraalVM native image

  • Bundles the native image of our function and the bootstrap file into a ZIP file.

FROM gradle:6.3.0-jdk11 as builder
COPY --chown=gradle:gradle . /home/application
WORKDIR /home/application
RUN ./gradlew build --no-daemon
FROM amazonlinux:2018.03.0.20191014.0 as graalvm


RUN yum install -y gcc gcc-c++ libc6-dev  zlib1g-dev curl bash zlib zlib-devel zip

ENV GRAAL_FILENAME graalvm-ce-${JDK_VERSION}-linux-amd64-${GRAAL_VERSION}.tar.gz


RUN tar -zxvf /tmp/${GRAAL_FILENAME} -C /tmp \
    && mv /tmp/graalvm-ce-${JDK_VERSION}-${GRAAL_VERSION} /usr/lib/graalvm

RUN rm -rf /tmp/*
CMD ["/usr/lib/graalvm/bin/native-image"]

FROM graalvm
COPY --from=builder /home/application/ /home/application/
WORKDIR /home/application
RUN /usr/lib/graalvm/bin/gu install native-image
RUN /usr/lib/graalvm/bin/native-image --no-server -cp build/libs/complete-*-all.jar
RUN chmod 777 bootstrap
RUN chmod 777 complete
RUN zip -j bootstrap complete
ENTRYPOINT ["/home/application/complete"]

The above file references the name used in the file.

It includes a bash script to generate the ZIP file:
docker build . -t complete
mkdir -p build
docker run --rm --entrypoint cat complete  /home/application/ > build/

Upload the file

Execute ./ and once you have a ZIP file, upload it

upload function code

3.3 Handler

The handler used is the one created at MicronautLambdaRuntime.

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

However, I like to specify it in the console as well:

That value is exposed as an environment variable.


3.4 Test

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

test event

You should see a 200 response:

test result

4 Next Steps

5 Help with Micronaut

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

OCI is Home to Micronaut.

Meet the Team