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.

Authors: Sergio del Amo

Micronaut Version: 4.3.3

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

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:

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=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.
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.

5. Handler

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

src/main/java/example/micronaut/FunctionRequestHandler.java
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;
import java.util.Collections;

public class FunctionRequestHandler extends MicronautRequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    @Inject
    JsonMapper objectMapper;

    @Override
    public APIGatewayProxyResponseEvent execute(APIGatewayProxyRequestEvent input) {
        APIGatewayProxyResponseEvent response = new APIGatewayProxyResponseEvent();
        try {
            String json = new String(objectMapper.writeValueAsBytes(Collections.singletonMap("message", "Hello World")));
            response.setStatusCode(200);
            response.setBody(json);
        } catch (IOException e) {
            response.setStatusCode(500);
        }
        return response;
    }
}

6. Handler Test

Write a test which verifies the function behaviour:

src/test/java/example/micronaut/FunctionRequestHandlerTest.java
package example.micronaut;

import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent;
import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyResponseEvent;
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;

class FunctionRequestHandlerTest {

    private static FunctionRequestHandler handler;

    @BeforeAll
    public static void setupServer() {
        handler = new FunctionRequestHandler();
    }

    @AfterAll
    public static void stopServer() {
        if (handler != null) {
            handler.getApplicationContext().close();
        }
    }

    @Test
    void testHandler() {
        APIGatewayProxyRequestEvent request = new APIGatewayProxyRequestEvent();
        request.setHttpMethod("GET");
        request.setPath("/");
        APIGatewayProxyResponseEvent response = handler.execute(request);
        assertEquals(200, response.getStatusCode().intValue());
        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.

  • Invoke the execute method of the handler.

7. Testing the Application

To run the tests:

./gradlew test

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

8. Lambda

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

create function

Enable function URLs and set Auth Type as NONE.

enable function url

8.1. Upload Code

Create an executable jar including all dependencies:

./gradlew shadowJar

Upload it:

upload function code

8.2. Handler

As Handler, set:

example.micronaut.FunctionRequestHandler

handler 2

8.3. 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"}

9. Next steps

Explore more features with Micronaut Guides.

Read more about:

10. Help with the Micronaut Framework

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

11. 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…​).