Create and Deploy a Micronaut Gateway Function as a Google Cloud Function

This guide describes how to create a Micronaut Gateway function, deploy it using Google Cloud Functions, and enable HTTP access to it. The application is compiled into a native executable using GraalVM Native Image and then built into a container image which can be deployed on Google Cloud Run.

Google Cloud Functions is a scalable, pay-as-you-go Functions as a Service (FaaS) product. It lets you run code for virtually any type of application or backend service without provisioning or managing servers. You can deploy code to Google Cloud Functions by uploading a Java JAR file. Google Cloud Run enables you to deploy scalable containerized applications written in any language on a fully managed platform. Similarly to Google Cloud Functions, the service provisions and manages servers for you.

Prerequisites #

Follow the steps below to create the application from scratch. However, you can also download the completed example in Java:

A note regarding your development environment

Consider using Visual Studio Code that provides native support for developing applications with the Graal Cloud Native extension.

Note: If you use IntelliJ IDEA, enable annotation processing.

1. Create the Application #

This section describes how to create an application for a simple online store. The store will provide information about available items and enable the user to order items. An HTTP controller is responsible for the API implementation and a service stores the availability of items.

Create an application using the GCN Launcher.

  1. Open the GCN Launcher in advanced mode.

  2. Create a new project using the following selections.
    • Project Type: Gateway Function
    • Project Name: gcp-serverless-demo
    • Base Package: com.example (Default)
    • Clouds: GCP
    • Language: Java (Default)
    • Build Tool: Gradle (Groovy) or Maven
    • Test Framework: JUnit (Default)
    • Java Version: 17 (Default)
    • Micronaut Version: (Default)
    • Cloud Services: None
    • Features: GraalVM Native Image, Micronaut Validation
    • Sample Code: No
  3. Click Generate Project. The GCN Launcher creates an application with the default package com.example in a directory named gcp-serverless-demo. The application ZIP file will be downloaded in your default downloads directory. Unzip it, open in your code editor, and proceed to the next steps.

Alternatively, use the GCN CLI as follows:

gcn create-gateway-function com.example.gcp-serverless-demo \
    --clouds=gcp \
    --features=graalvm,validation \
    --build=gradle \
gcn create-gateway-function com.example.gcp-serverless-demo \
    --clouds=gcp \
    --features=graalvm,validation \
    --build=maven \

For more information, see Using the GCN CLI.

1.1. StoreItem #

The launcher created a StoreItem model to represent an item in the store in the file lib/src/main/java/com/example/ with the following contents:

package com.example;

import io.micronaut.core.annotation.Introspected;
import io.micronaut.core.annotation.NonNull;

import io.micronaut.serde.annotation.Serdeable;
import jakarta.validation.constraints.Min;
import jakarta.validation.constraints.NotBlank;

@Introspected // <1>
public class StoreItem {

    private final String name;

    private final String description;

    private int numberInStorage;

    public StoreItem(String name, String description, int numberInStorage) { // <2> = name;
        this.description = description;
        this.numberInStorage = numberInStorage;

    public String getName() {
        return name;

    public String getDescription() {
        return description;

    public Integer getNumberInStorage() {
        return numberInStorage;

    public void setNumberInStorage(Integer numberInStorage) {
        this.numberInStorage = numberInStorage;

1 The @Introspected annotation enables Micronaut to serialize and deserialize the model from different formats including JSON. This provides the ability to use the type inside HTTP requests or responses.

2 The model has fields to store the item’s name, description, and number available.

1.2. StoreController #

The launcher generated an HTTP controller in the file lib/src/main/java/com/example/, as follows:

package com.example;

import io.micronaut.http.HttpResponse;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.PathVariable;
import io.micronaut.http.annotation.Post;
import io.micronaut.http.exceptions.HttpStatusException;
import jakarta.validation.constraints.Min;
import jakarta.validation.constraints.NotBlank;
import jakarta.validation.constraints.NotNull;

import java.util.Collection;

import static io.micronaut.http.HttpStatus.BAD_REQUEST;
import static io.micronaut.http.HttpStatus.NOT_FOUND;

@Controller("/store") // <1>
class StoreController {

    private final StorageService storageService;

    StoreController(StorageService storageService) { // <2>
        this.storageService = storageService;

    @Get("/all") // <3>
    Collection<StoreItem> listAllItems() {
        return storageService.getItems();

    @Get("/available") // <4>
    Collection<StoreItem> listAvailableItems() {
        return storageService.getItems().stream()
                .filter(i -> i.getNumberInStorage() > 0)

    @Post(uri = "/order/{name}/{amount}", consumes = "*/*") // <5>
    HttpResponse<StoreItem> orderItem(@NotBlank @PathVariable String name, @Min(1) int amount) {
        if (storageService.findItem(name).isEmpty()) {
            throw new HttpStatusException(NOT_FOUND, "Item '" + name + "' not found");
        try {
            storageService.orderItem(name, amount);
        } catch (StorageService.StorageException e) {
            throw new HttpStatusException(BAD_REQUEST, "Could not order item '" + name + "'. " + e.getMessage());
        return HttpResponse.ok(storageService.findItem(name).orElse(null));

1 The class is defined as a controller with the @Controller annotation mapped to the path /store.

2 Use Micronaut argument injection to inject a StorageService bean by defining it as the constructor argument. You will create the StorageService in next section.

3 The @Get annotation maps the listAllItems method to an HTTP GET request on /store/all.

4 The @Get annotation maps the listAvailableItems method to an HTTP GET request on /store/available.

5 The @Post annotation maps the orderItem method to an HTTP POST request on /store/order/{name}/{amount}. Use the consumes argument to specify which content-types are allowed in the request. Throwing HttpStatusException will set the corresponding HTTP status in the response.

1.3. StorageService #

  1. The launcher created an interface for a service that represents the store’s inventory in lib/src/main/java/com/example/

     package com.example;
     import io.micronaut.core.annotation.NonNull;
     import jakarta.validation.constraints.Min;
     import jakarta.validation.constraints.NotBlank;
     import java.util.Collection;
     import java.util.Optional;
     public interface StorageService { // <1>
         Collection<StoreItem> getItems();
         Optional<StoreItem> findItem(@NonNull @NotBlank String name);
         void orderItem(@NonNull @NotBlank String name, @Min(1) int amount);
         class StorageException extends RuntimeException { // <2>
             StorageException(String message) {

    1 The storage service provides information about all the items, finds an item by its name, and can place an order for an item.

    2 The class includes a custom exception that thrown in case of invalid requests to storage.

  2. The launcher generated an implementation of the service interface in lib/src/main/java/com/example/

     package com.example;
     import io.micronaut.context.annotation.Requires;
     import io.micronaut.core.annotation.NonNull;
     import jakarta.inject.Singleton;
     import java.util.ArrayList;
     import java.util.Collection;
     import java.util.List;
     import java.util.Optional;
     @Singleton // <1>
     @Requires(missingBeans = StorageService.class) // <2>
     class DefaultStorageService implements StorageService {
         protected List<StoreItem> items = List.of( // <3>
             new StoreItem("chair", "A black chair with 4 legs", 10),
             new StoreItem("table", "A quality dining table", 6),
             new StoreItem("sofa", "A grey sofa", 2),
             new StoreItem("bookshelf", "A futuristic-looking bookshelf", 0)
         public Collection<StoreItem> getItems() {
             return items;
         public Optional<StoreItem> findItem(@NonNull String name) {
             return -> item.getName().equals(name)).findFirst();
         public void orderItem(@NonNull String name, int amount) {
             findItem(name).ifPresentOrElse(item -> {
                 if (item.getNumberInStorage() >= amount) {
                     item.setNumberInStorage(item.getNumberInStorage() - amount);
                 } else {
                     throw new StorageException("Insufficient amount in storage");
             }, () -> { throw new StorageException("Item not found in storage"); });

    1 Use jakarta.inject.Singleton to designate a class as a singleton.

    2 The @Requires(missingBeans = StorageService.class) annotation specifies that this implementation should only be used if no other implementations could be found.

    3 The implementation stores the items in a List and populates some sample items in the list.

If you wish to implement a more advanced StorageService to be used instead of this one, annotate your implementation with @Singleton as shown above. Use the @Requires(env = "ec2") annotation to make it specific to AWS . Visit the Database Module for details about how to store and manipulate data in a database.

1.4. Tests to Verify Application Logic #

The launcher created a test class for the controller in gcp/src/test/java/com/example/, as follows:

package com.example;

import io.micronaut.context.annotation.Property;
import io.micronaut.context.annotation.Requires;
import io.micronaut.http.HttpResponse;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.Post;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.http.client.exceptions.HttpClientResponseException;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import jakarta.inject.Inject;
import jakarta.inject.Singleton;
import org.junit.jupiter.api.Test;

import java.util.ArrayList;
import java.util.List;

import static io.micronaut.http.HttpStatus.BAD_REQUEST;
import static io.micronaut.http.HttpStatus.NOT_FOUND;
import static io.micronaut.http.HttpStatus.OK;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertThrows;

@MicronautTest // <1>
@Property(name = "use-test-storage-service", value = "true")
class StoreControllerTest {

    StoreClient client;

    void testAvailableItems() {
        List<StoreItem> availableItems = client.getAvailable();

        assertEquals(2, availableItems.size());
        assertEquals("pot", availableItems.get(1).getName());
        assertEquals(10, availableItems.get(1).getNumberInStorage());

    void testNotFoundException() {
        HttpResponse<?> response = client.order("lamp", 1);

        assertEquals(NOT_FOUND, response.getStatus());

    void testNotSufficientException() {
        HttpClientResponseException e = assertThrows(HttpClientResponseException.class, () -> {
            client.order("pot", 100);

        assertEquals(BAD_REQUEST, e.getStatus());

    void testOrderRequest() {
        StoreItem plate = client.getAll().stream()
                .filter(i -> i.getName().equals("plate"))
        assertEquals(100, plate.getNumberInStorage());

        HttpResponse<StoreItem> response = client.order("plate", 10);
        assertEquals(OK, response.getStatus());
        assertEquals("plate", response.body().getName());
        assertEquals(90, response.body().getNumberInStorage());

    @Requires(property = "use-test-storage-service", value = "true")
    static class TestStorageService extends DefaultStorageService {
        TestStorageService() { // <2>
            items = List.of(
                    new StoreItem("plate", "A large plate", 100),
                    new StoreItem("pot", "A cooking pot", 10),
                    new StoreItem("pan", "A large pan", 0)

    @Client("/store") // <3>
    interface StoreClient {
        @Get("/all") // <4>
        List<StoreItem> getAll();

        @Get("/available") // <4>
        List<StoreItem> getAvailable();

        @Post("/order/{name}/{amount}") // <4>
        HttpResponse<StoreItem> order(String name, Integer amount);

1 Annotate the class with @MicronautTest so the Micronaut framework will initialize the application context. This enables you to inject beans using the Jakarta @Inject annotation and to send requests to the StoreController defined in the application. Configure this test to use an identified context using the @Property(name = "use-test-storage-service", value = "true") annotation.

2 Create a mock implementation of StorageService so that the test is independent of the current state of the storage. The @Requires(property = "use-test-storage-service", value = "true") means that the bean should only be available if the specified property is set.

3 Create a Micronaut Declarative Client with the same /store path to send requests to the controller.

4 Create three tests using the defined client and assuming that TestStorageService is used.

2. Run the Tests #

Run the tests using the following command:

./gradlew test

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

./mvnw test

Although you created this application to run on the Google Cloud Function runtime, the tests should run successfully on your local machine.

Furthermore, Micronaut has a test implementation that simulates the Google Cloud environment. Since sequential requests to a function may be processed by different instances, Micronaut creates a separate environment for each request in test.

3. Create a Google Cloud Function #

3.1. Create a Google Cloud Project #

Create a project in GCP and switch to it:

export PROJECT_ID=gcn-serverless-demo
gcloud projects create $PROJECT_ID
gcloud config set project $PROJECT_ID

Note: The project id must be unique, so you need to provide a different one.

Note: If you want to switch to an existing project use gcloud projects list to list all the existing projects.

Enable the required services for the new project:

gcloud services enable
gcloud services enable

3.2. Deploy the Application to a Google Cloud Function #

Create a JAR file from the application, as follows:

./gradlew gcp:clean gcp:shadowJar

The command should create the file gcp/build/libs/gcp-1.0-SNAPSHOT-all.jar. The JAR file is the only one in the directory, which is required for correct deployment.

Create a function from the JAR file with the name gcn-function: set the entry point, the Java runtime, the trigger, and the source.

gcloud functions deploy gcn-function \
    --entry-point io.micronaut.gcp.function.http.HttpFunction \
    --runtime java17 \
    --trigger-http \
    --source gcp/build/libs
./mvnw package -pl gcp -am

The command should create the file gcp/target/gcp-1.0-SNAPSHOT.jar.

To deploy, move the JAR file to an empty directory:

mkdir gcp/target/jar
mv gcp/target/gcp-1.0-SNAPSHOT.jar gcp/target/jar/gcp.jar

Create a function from the JAR file with the name gcn-function: set the entry point, the Java runtime, the trigger, and the source.

gcloud functions deploy gcn-function \
    --entry-point io.micronaut.gcp.function.http.HttpFunction \
    --runtime java17 \
    --trigger-http \
    --source gcp/target/jar

Note: You might need to set a billing account for your project to use Google Cloud Functions. Visit Cloud Functions Console to verify that you can create functions for your project.

Note: See the Micronaut Google Cloud Functions Support documentation for more configuration information.

4. Test the Google Cloud Function Deployment #

Now the application is deployed to GCP, you can test it by sending requests.

  1. Define an environment variable for the hostname of your gateway:

    export TRIGGER_URL=$(gcloud functions describe gcn-function \

    Note: On Windows, use set TRIGGER_URL=<hostname> to set the environment variable and %GATEWAY_HOSTNAME% to access it. Or you can skip this step and paste the hostname for each of the following commands.

  2. Use curl to retrieve all the items:

    curl $TRIGGER_URL/store/all
     [{"name": "chair", "description": "A black chair with 4 legs", "numberInStorage": 10},
     {"name": "table", "description": "A quality dining table", "numberInStorage": 6},
     {"name": "sofa", "description": "A grey sofa", "numberInStorage": 2},
     {"name": "bookshelf", "description": "A futuristic-looking bookshelf", "numberInStorage": 0}]
  3. Get an error when attempting to order too many items:

    curl -X POST $TRIGGER_URL/store/order/table/10
     {"message": "Bad Request",
       "_embedded": {
         "errors": [{
           "message": "Could not order item 'table'. Insufficient amount in storage"
       }, ...
  4. Order an item and print the response status code:

    curl -X POST -w "\nStatus code: %{http_code}" $TRIGGER_URL/store/order/table/6
     {"message": "Bad Request",
       "_embedded": {"errors": [{"message": "Could not order item 'table'. Insufficient amount in storage"}]},
     Status code: 400
  5. Get the available items:

    curl $TRIGGER_URL/store/available
     [{"name": "chair", "description": "A black chair with 4 legs", "numberInStorage": 10},
     {"name": "sofa", "description": "A grey sofa", "numberInStorage": 2}]

5. Deploy a Native Executable with Google Cloud Run #

In this section you will use GraalVM Native Image to create a native executable from your Java application and then deploy it to Google Cloud Run.

5.1. Configure the Application #

Reconfigure the Micronaut application to run standalone instead of using the Google Cloud Function environment.

In the gcp/build.gradle file, set the runtime to netty:

micronaut {

Add the following dependency:


In the gcp/pom.xml file set the micronaut.runtime property to netty.

Add the following dependency:


5.2. Deploy the Application to Container Registry #

Authenticate docker with Google Cloud Registry (GCR) as shown below. (This will give docker the necessary permissions to push container images to the GCR.)

gcloud auth configure-docker

Push the container image of your application to GCR, as follows:

Add the following snippet to the gcp/build.gradle file:
tasks.named('dockerBuild') {
    images = ["${System.getProperty("projectId")}/gcn-function:latest"]
Run with the GCP project id:
./gradlew gcp:dockerPushNative -DprojectId=$PROJECT_ID
./mvnw install
./mvnw clean deploy -pl gcp \$PROJECT_ID/gcn-function:latest \

NOTE: If the push fails you can retry it with the following command:

docker push

5.3. Create a Google Cloud Run Service #

Enable Google Cloud Run and start a service using the container image you just pushed:

gcloud services enable
gcloud run deploy gcn-function \$PROJECT_ID/gcn-function:latest \
    --platform managed \

Specify the region in which your application should run.

Use the following command to retrieve the URL (replace [REGION] with your region, for example, us-east1):

export TRIGGER_URL=$(gcloud run services describe gcn-function \
    --region [REGION] --format 'value(status.url)')

Repeat steps from section 4 to test the application.

Summary #

This guide demonstrated how to create a Micronaut application, compile it into a native executable and run it as a Google Cloud Function.