Deploy a Micronaut application to AWS Lambda Java 11 Runtime

Learn how to distribute a Micronaut application to AWS Lambda 11 Runtime

Authors: Sergio del Amo

Micronaut Version: 3.9.2

1. Getting Started

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

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.

Download and unzip the source

4. Writing the Application

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

mn create-app example.micronaut.micronautguide \
    --features=aws-lambda,amazon-api-gateway \
    --build=gradle
    --lang=java

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.

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

If you use Micronaut Launch, select Micronaut Application as application type and add aws-lambda, and amazon-api-gateway features.

If you have an existing Micronaut application and want to add the functionality described here, you can view the dependency and configuration changes from the specified features and apply those changes to your application.

Setup IntelliJ IDEA to develop Micronaut Applications.

The generated application contains a HomeController. It responds to POST requests to /.

src/main/java/example/micronaut/HomeController.java

package example.micronaut;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import java.util.Collections;
import java.util.Map;

@Controller
public class HomeController {

    @Get
    public Map<String, Object> index() {
        return Collections.singletonMap("message", "Hello World");
    }
}

The class is defined as a controller with the @Controller annotation mapped to the path /.
The @Get annotation maps HTTP requests to / to the index method.

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

src/test/java/example/micronaut/HomeControllerTest.java

package example.micronaut;
import com.amazonaws.serverless.exceptions.ContainerInitializationException;
import com.amazonaws.serverless.proxy.internal.testutils.MockLambdaContext;
import com.amazonaws.serverless.proxy.model.AwsProxyRequest;
import com.amazonaws.serverless.proxy.model.AwsProxyResponse;
import com.amazonaws.services.lambda.runtime.Context;
import com.fasterxml.jackson.core.JsonProcessingException;
import io.micronaut.function.aws.proxy.MicronautLambdaHandler;
import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;

import static org.junit.jupiter.api.Assertions.assertEquals;

public class HomeControllerTest {

    private static MicronautLambdaHandler handler;
    private static Context lambdaContext = new MockLambdaContext();

    @BeforeAll
    public static void setupSpec() {
        try {
            handler = new MicronautLambdaHandler();
        } catch (ContainerInitializationException e) {
            e.printStackTrace();
        }
    }

    @AfterAll
    public static void cleanupSpec() {
        handler.getApplicationContext().close();
    }

    @Test
    void testHandler() throws JsonProcessingException {
        AwsProxyRequest request = new AwsProxyRequest();
        request.setHttpMethod("GET");
        request.setPath("/");
        AwsProxyResponse response = handler.handleRequest(request, lambdaContext);
        assertEquals(200, response.getStatusCode());
        assertEquals("{\"message\":\"Hello World\"}",  response.getBody());
    }
}

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 Java 11 (Correto).

6.1. Upload Code

Create an executable jar including all dependencies:

./gradlew shadowJar

Upload it:

6.2. Handler

As Handler, set:

io.micronaut.function.aws.proxy.MicronautLambdaHandler

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:

You should see a 200 response:

7. Next steps

Explore more features with Micronaut Guides.

8. Help with the Micronaut Framework

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

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