Quick Guide: Micronaut on AWS Lambda

Here you will:

• Generate a project with the Micronaut CLI (or clone this repository for the full application).
• Code a simple function.
• Unit test the function using Micronaut’s test framework.
• Build an AWS native image.
• Deploy to AWS Lambda with the AWS CLI.

Setup

Install:

• Micronaut
• Docker
• AWS CLI

Micronaut comes with a convenient CLI to create applications and functions. Create a project called micronaut-greeter with everything required to deploy to AWS, by inlcuding aws-api-gateway-graal feature:

mn create-app micronaut-greeter --features aws-api-gateway-graal

Alternatively, clone this application instead and skip to the build section of this guide.

Code

Create a controller and inject a service that does the greeting:

@Controller
public class RocketController {

    @Inject
    private RadioService radio;

    @Get("/greet")
    public String greet() {
        return radio.greet();
    }
}

Our injected service looks like this:

@Singleton
public class RadioService {

    public String greet() {
        return "Hello from Micronaut";
    }
}

That's all the code we need.

Test

Micronaut Test framework makes it very simple to create an HTTP client dedicated to our application:

@Client("/")
public interface RadioClient {

    @Get("/greet")
    String greet();

}

All the necessary HTTP client code is generated behind the scenes.

Inject the client into a class annotation with @MicronautTest:

@MicronautTest
public class RocketTest {

    @Inject
    RadioClient client;

    @Test
    public void test_greeter_response_is_as_expected() {
        String response = client.greet();
        assertEquals(response, "Hello from Micronaut");
    }
}

Build

The aws-api-gateway-graal feature generated a Docker file that we can use to build a native image for AWS Lambda.

Execute the following to build the image:

docker build . -t micronaut-greeter
mkdir build
docker run --rm --entrypoint cat micronaut-greeter /home/application/function.zip > build/function.zip

Deploy

Use the AWS CLI to create a Lamda function.

aws lambda create-function \
  --function-name micronaut-greeter \
  --zip-file fileb://build/function.zip \
  --handler function.handler \
  --runtime provided \
  --role arn:aws:iam::123456789012:role/lambda-role

Run

Test the endpint with the AWS CLI by executing the invoke command.

aws lambda invoke --function-name micronaut-greeter --payload '{"resource": "/{proxy+}","path": "/greet","httpMethod": "GET","pathParameters":{"proxy":"greet"},"requestContext":{"identity":{}}}' build/response.txt