Deploy a Serverless Micronaut function to AWS Lambda Java 11 Runtime

Learn how to distribute a serverless Micronaut function to AWS Lambda 11 Runtime

Authors: Sergio del Amo

Micronaut Version: 3.9.2

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.

If you want to respond to triggers such as queue events, S3 events, or single endpoints, you should opt to code your Micronaut functions as Serverless functions.

In this guide, we will deploy a Micronaut serverless function to AWS Lambda.

1. Getting Started

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.

Download and unzip the source

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=maven --lang=kotlin

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, select serverless function as application type and add the aws-lambda feature.

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

Setup IntelliJ IDEA to develop Micronaut Applications.

The application contains a class extending MicronautRequestHandler

src/main/kotlin/example/micronaut/FunctionRequestHandler.kt

package example.micronaut
import io.micronaut.function.aws.MicronautRequestHandler
import com.fasterxml.jackson.core.JsonProcessingException
import com.fasterxml.jackson.databind.ObjectMapper
import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent
import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyResponseEvent
import jakarta.inject.Inject
class FunctionRequestHandler : MicronautRequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent>() {
    @Inject
    lateinit var objectMapper: ObjectMapper

    override fun execute(input: APIGatewayProxyRequestEvent): APIGatewayProxyResponseEvent {
        val response = APIGatewayProxyResponseEvent()
        try {
            val json = objectMapper.writeValueAsString(mapOf("message" to "Hello World"))
            response.statusCode = 200
            response.body = json
        } catch (e: JsonProcessingException) {
            response.statusCode = 500
        }
        return response
    }
}

The class extends MicronautRequestHandler and defines input and output types.

An included test shows how to verify the function behaviour:

src/test/kotlin/example/micronaut/FunctionRequestHandlerTest.kt

package example.micronaut
import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent
import org.junit.jupiter.api.Assertions.assertEquals
import org.junit.jupiter.api.Test

class FunctionRequestHandlerTest {

    @Test
    fun testHandler() {
        val handler = FunctionRequestHandler()
        val request = APIGatewayProxyRequestEvent()
        request.httpMethod = "GET"
        request.path = "/"
        val response = handler.execute(request)
        assertEquals(200, response.statusCode.toInt())
        assertEquals("{\"message\":\"Hello World\"}", response.body)
        handler.close()
    }
}

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.

5. Testing the Application

To run the tests:

./mvnw test

6. Lambda

Create a Lambda Function. As a runtime, select Java 11 (Correto).

6.1. Upload Code

Create an executable jar including all dependencies:

./mvnw package

Upload it:

6.2. Handler

As Handler, set:

example.micronaut.FunctionRequestHandler

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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