Consul and the Micronaut Framework - Microservices Service Discovery

Use Consul service discovery to expose your Micronaut applications.

Authors: Sergio del Amo

Micronaut Version: 4.6.3

1. Getting Started

In this guide, we will create three microservices and register them with Consul Service discovery.

Consul is a distributed service mesh to connect, secure, and configure services across any runtime platform and public or private cloud

You will discover how the Micronaut framework eases Consul integration.

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 (e.g. IntelliJ IDEA)
JDK 21 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 App

Let’s describe the microservices you will build through the guide.

bookcatalogue - It returns a list of books. It uses a domain consisting of a book name and ISBN.
bookinventory - It exposes an endpoint to check whether a book has sufficient stock to fulfil an order. It uses a domain consisting of a stock level and ISBN.
bookrecommendation - It consumes previous services and exposes an endpoint which recommends book names which are in stock.

Initially we will hard-code the addresses where the different services are in the bookcatalogue service.

As shown in the previous image, the bookcatalogue hardcodes references to its collaborators.

In the second part of this guide we will use a discovery service.

About registration patterns

We will use a self‑registration pattern. Thus, each service instance is responsible for registering and deregistering itself with the service registry. Also, if required, a service instance sends heartbeat requests to prevent its registration from expiring.

Services register when they start up:

We will use client‑side service discovery, clients query the service registry, select an available instance, and make a request.

Setup IntelliJ IDEA to develop Micronaut Applications.

4.1. Catalogue Microservice

Create the bookcatalogue microservice using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-app --features=discovery-consul,management,graalvm example.micronaut.bookcatalogue --build=maven --lang=java

If you don’t specify the --build argument, Gradle with the Kotlin DSL 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 Micronaut Application as application type and add the discovery-consul, management, and graalvm features.

The previous command creates a directory named bookcatalogue and a Micronaut application inside it with default package example.micronaut.

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.

Diff

Create a BooksController class to handle incoming HTTP requests into the bookcatalogue microservice:

bookcatalogue/src/main/java/example/micronaut/BooksController.java

package example.micronaut;

import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;

import java.util.Arrays;
import java.util.List;

@Controller("/books") (1)
public class BooksController {

    @Get (2)
    public List<Book> index() {
        return Arrays.asList(
                new Book("1491950358", "Building Microservices"),
                new Book("1680502395", "Release It!"),
                new Book("0321601912", "Continuous Delivery:")
        );
    }
}

1	The class is defined as a controller with the @Controller annotation mapped to the path `/`.
2	The @Get annotation maps the `index` method to an HTTP GET request on `/books`.

The previous controller responds a List<Book>. Create the Book POJO:

bookcatalogue/src/main/java/example/micronaut/Book.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import io.micronaut.serde.annotation.Serdeable;

import jakarta.validation.constraints.NotBlank;
import java.util.Objects;

@Serdeable
public class Book {

    @NonNull
    @NotBlank
    private final String isbn;

    @NonNull
    @NotBlank
    private final String name;

    public Book(@NonNull @NotBlank String isbn,
                @NonNull @NotBlank String name) {
        this.isbn = isbn;
        this.name = name;
    }

    @NonNull
    public String getIsbn() {
        return isbn;
    }

    @NonNull
    public String getName() {
        return name;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Book book = (Book) o;
        return Objects.equals(isbn, book.isbn) && Objects.equals(name, book.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(isbn, name);
    }
}

Write a test:

bookcatalogue/src/test/java/example/micronaut/BooksControllerTest.java

package example.micronaut;

import io.micronaut.core.type.Argument;
import io.micronaut.http.HttpRequest;
import io.micronaut.http.client.HttpClient;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import jakarta.inject.Inject;
import org.junit.jupiter.api.Test;

import java.util.List;

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

@MicronautTest (1)
public class BooksControllerTest {

    @Inject
    @Client("/")
    HttpClient client; (2)

    @Test
    public void testRetrieveBooks() {
        HttpRequest<?> request = HttpRequest.GET("/books"); (3)
        List<Book> books = client.toBlocking().retrieve(request, Argument.listOf(Book.class)); (4)

        assertEquals(3, books.size());
        assertTrue(books.contains(new Book("1491950358", "Building Microservices")));
        assertTrue(books.contains(new Book("1680502395", "Release It!")));
    }
}

1	Annotate the class with `@MicronautTest` so the Micronaut framework will initialize the application context and the embedded server. More info.
2	Inject the `HttpClient` bean and point it to the embedded server.
3	Creating HTTP Requests is easy thanks to the Micronaut framework fluid API.
4	Parse easily JSON into Java objects.

Edit application.yml

Since Micronaut Framework 4.0, to use YAML configuration, you have to add the YAML dependency.

bookcatalogue/src/main/resources/application.yml

micronaut:
  application:
    name: bookcatalogue (1)

1	Configure the application name. The application name will be used by the discovery service.

Modify the Application class to use dev as a default environment:

The Micronaut framework supports the concept of one or many default environments. A default environment is one that is only applied if no other environments are explicitly specified or deduced.

bookcatalogue/src/main/java/example/micronaut/Application.java

package example.micronaut;

import io.micronaut.runtime.Micronaut;

import static io.micronaut.context.env.Environment.DEVELOPMENT;

public class Application {

    public static void main(String[] args) {
        Micronaut.build(args)
                .mainClass(Application.class)
                .defaultEnvironments(DEVELOPMENT)
                .start();
    }
}

Create src/main/resources/application-dev.yml. The Micronaut framework applies this configuration file only for the dev environment.

bookcatalogue/src/main/resources/application-dev.yml

micronaut:
  server:
    port: 8081 (1)

1	Configure the application to listen on port 8081

Create a file named application-test.yml which is used in the test environment:

bookcatalogue/src/test/resources/application-test.yml

consul:
  client:
    registration:
      enabled: false

Run the unit test:

bookcatalogue

./mvnw test

4.2. Inventory Microservice

Create the bookinventory microservice using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-app --features=discovery-consul,management,graalvm example.micronaut.bookinventory --build=maven --lang=java

If you use Micronaut Launch, select Micronaut Application as application type and add the discovery-consul, management, and graalvm features.

The previous command creates a directory named bookinventory and a Micronaut application inside it with default package example.micronaut.

Diff

Create a Controller:

bookinventory/src/main/java/example/micronaut/BooksController.java

package example.micronaut;

import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.Produces;

import jakarta.validation.constraints.NotBlank;
import java.util.Optional;

import static io.micronaut.http.MediaType.TEXT_PLAIN;

@Controller("/books") (1)
public class BooksController {

    @Produces(TEXT_PLAIN) (2)
    @Get("/stock/{isbn}") (3)
    public Boolean stock(@NotBlank String isbn) { (1)
        return bookInventoryByIsbn(isbn).map(bi -> bi.getStock() > 0).orElse(null);
    }

    private Optional<BookInventory> bookInventoryByIsbn(String isbn) {
        if (isbn.equals("1491950358")) {
            return Optional.of(new BookInventory(isbn, 4));
        }
        if (isbn.equals("1680502395")) {
            return Optional.of(new BookInventory(isbn, 0));
        }
        return Optional.empty();
    }
}

1	The class is defined as a controller with the @Controller annotation mapped to the path `/books`.
2	By default, `Content-Type` of a controller response is `application/json` : override this with `text/plain` since we are returning a String, not a JSON object.
3	The @Get annotation maps the `index` method to an HTTP GET request on `/books/stock/{isbn}`.

Create the POJO used by the controller:

bookinventory/src/main/java/example/micronaut/BookInventory.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import io.micronaut.serde.annotation.Serdeable;

import jakarta.validation.constraints.NotBlank;
import java.util.Objects;

@Serdeable
public class BookInventory {

    @NonNull
    @NotBlank
    private final String isbn;

    private final int stock;

    public BookInventory(@NonNull @NotBlank String isbn,
                         int stock) {
        this.isbn = isbn;
        this.stock = stock;
    }

    @NonNull
    public String getIsbn() {
        return isbn;
    }

    public int getStock() {
        return stock;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        BookInventory that = (BookInventory) o;
        return stock == that.stock && Objects.equals(isbn, that.isbn);
    }

    @Override
    public int hashCode() {
        return Objects.hash(isbn, stock);
    }
}

Write a test:

bookinventory/src/test/java/example/micronaut/BooksControllerTest.java

package example.micronaut;

import io.micronaut.http.HttpRequest;
import io.micronaut.http.HttpResponse;
import io.micronaut.http.client.HttpClient;
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 org.junit.jupiter.api.Test;

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.assertThrows;
import static org.junit.jupiter.api.Assertions.assertTrue;

@MicronautTest
public class BooksControllerTest {

    @Inject
    @Client("/")
    HttpClient httpClient;

    @Test
    public void testBooksController() {
        HttpResponse<Boolean> rsp = httpClient.toBlocking().exchange(
                HttpRequest.GET("/books/stock/1491950358"), Boolean.class);
        assertEquals(OK, rsp.status());
        assertTrue(rsp.body());
    }

    @Test
    public void testBooksControllerWithNonExistingIsbn() {
        HttpClientResponseException thrown = assertThrows(HttpClientResponseException.class, () -> {
            httpClient.toBlocking().exchange(HttpRequest.GET("/books/stock/XXXXX"), Boolean.class);
        });

        assertEquals(NOT_FOUND, thrown.getResponse().getStatus());
    }
}

Edit application.yml

bookinventory/src/main/resources/application.yml

micronaut:
  application:
    name: bookinventory (1)

1	Configure the application name. The name will be used later in the guide.

Modify the Application class to use dev as a default environment:

The Micronaut framework supports the concept of one or many default environments. A default environment is one that is only applied if no other environments are explicitly specified or deduced.

bookinventory/src/main/java/example/micronaut/Application.java

package example.micronaut;

import io.micronaut.runtime.Micronaut;

import static io.micronaut.context.env.Environment.DEVELOPMENT;

public class Application {

    public static void main(String[] args) {
        Micronaut.build(args)
                .mainClass(Application.class)
                .defaultEnvironments(DEVELOPMENT)
                .start();
    }
}

Create src/main/resources/application-dev.yml. The Micronaut framework applies this configuration file only for the dev environment.

bookinventory/src/main/resources/application-dev.yml

micronaut:
  server:
    port: 8082 (1)

1	Configure the application to listen on port 8082

Create a file named application-test.yml which is used in the test environment:

bookinventory/src/test/resources/application-test.yml

consul:
  client:
    registration:
      enabled: false

Run the unit test:

bookinventory

./mvnw test

4.3. Recommendation Microservice

Create the bookrecommendation microservice using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-app --features=discovery-consul,management,reactor,graalvm example.micronaut.bookrecommendation --build=maven --lang=java

If you use Micronaut Launch, select Micronaut Application as application type and add the discovery-consul, management, reactor, and graalvm features.

The previous command creates a directory named bookrecommendation and a Micronaut application inside it with default package example.micronaut.

Diff

Create an interface to map operations with bookcatalogue, and a Micronaut Declarative HTTP Client to consume it.

bookrecommendation/src/main/java/example/micronaut/BookCatalogueOperations.java

package example.micronaut;

import org.reactivestreams.Publisher;

public interface BookCatalogueOperations {
    Publisher<Book> findAll();
}

bookrecommendation/src/main/java/example/micronaut/BookCatalogueClient.java

package example.micronaut;


import io.micronaut.http.annotation.Get;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.retry.annotation.Recoverable;
import org.reactivestreams.Publisher;

@Client("http://localhost:8081") (1)
@Recoverable(api = BookCatalogueOperations.class)

interface BookCatalogueClient extends BookCatalogueOperations {

    @Get("/books")
    Publisher<Book> findAll();
}

1	Use `@Client` to use declarative HTTP Clients. You can annotate interfaces or abstract classes. You can use the `id` member to provide a service identifier or specify the URL directly as the annotation’s value.

The client returns a POJO. Create it in the bookrecommendation:

bookrecommendation/src/main/java/example/micronaut/Book.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import io.micronaut.serde.annotation.Serdeable;

import jakarta.validation.constraints.NotBlank;
import java.util.Objects;

@Serdeable
public class Book {

    @NonNull
    @NotBlank
    private final String isbn;

    @NonNull
    @NotBlank
    private final String name;

    public Book(@NonNull @NotBlank String isbn,
                @NonNull @NotBlank String name) {
        this.isbn = isbn;
        this.name = name;
    }

    @NonNull
    public String getIsbn() {
        return isbn;
    }

    @NonNull
    public String getName() {
        return name;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Book book = (Book) o;
        return Objects.equals(isbn, book.isbn) && Objects.equals(name, book.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(isbn, name);
    }
}

Create an interface to map operations with bookinventory, and a Micronaut Declarative HTTP Client to consume it.

bookrecommendation/src/main/java/example/micronaut/BookInventoryOperations.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import reactor.core.publisher.Mono;

import jakarta.validation.constraints.NotBlank;

public interface BookInventoryOperations {
    Mono<Boolean> stock(@NonNull @NotBlank String isbn);
}

bookrecommendation/src/main/java/example/micronaut/BookInventoryClient.java

package example.micronaut;


import io.micronaut.core.annotation.NonNull;
import io.micronaut.http.annotation.Consumes;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.retry.annotation.Recoverable;
import reactor.core.publisher.Mono;

import jakarta.validation.constraints.NotBlank;

import static io.micronaut.http.MediaType.TEXT_PLAIN;

@Client("http://localhost:8082") (1)
@Recoverable(api = BookInventoryOperations.class)

interface BookInventoryClient extends BookInventoryOperations {

    @Consumes(TEXT_PLAIN)
    @Get("/books/stock/{isbn}")
    Mono<Boolean> stock(@NonNull @NotBlank String isbn);
}

1	Use `@Client` to use declarative HTTP Clients. You can annotate interfaces or abstract classes. You can use the `id` member to provide a service identifier or specify the URL directly as the annotation’s value.

Create a Controller which injects both clients.

bookrecommendation/src/main/java/example/micronaut/BookController.java

package example.micronaut;

import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;

@Controller("/books") (1)
public class BookController {

    private final BookCatalogueOperations bookCatalogueOperations;
    private final BookInventoryOperations bookInventoryOperations;

    public BookController(BookCatalogueOperations bookCatalogueOperations,
                          BookInventoryOperations bookInventoryOperations) { (2)
        this.bookCatalogueOperations = bookCatalogueOperations;
        this.bookInventoryOperations = bookInventoryOperations;
    }

    @Get (3)
    public Publisher<BookRecommendation> index() {
        return Flux.from(bookCatalogueOperations.findAll())
                .flatMap(b -> Flux.from(bookInventoryOperations.stock(b.getIsbn()))
                        .filter(Boolean::booleanValue)
                        .map(rsp -> b)
                ).map(book -> new BookRecommendation(book.getName()));
    }
}

1	The class is defined as a controller with the @Controller annotation mapped to the path `/books`.
2	Clients are injected via constructor injection
3	The @Get annotation maps the `index` method to an HTTP GET request on `/books`.

The previous controller returns a Publisher<BookRecommendation>. Create the BookRecommendation POJO:

bookrecommendation/src/main/java/example/micronaut/BookRecommendation.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import io.micronaut.serde.annotation.Serdeable;

import jakarta.validation.constraints.NotBlank;

@Serdeable
public class BookRecommendation {

    @NonNull
    @NotBlank
    private final String name;

    public BookRecommendation(@NonNull @NotBlank String name) {
        this.name = name;
    }

    @NonNull
    public String getName() {
        return name;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        BookRecommendation that = (BookRecommendation) o;

        return name.equals(that.name);
    }

    @Override
    public int hashCode() {
        return name.hashCode();
    }
}

BookCatalogueClient and BookInventoryClient will fail to consume the bookcatalogue and bookinventory during the tests phase.

Using the @Fallback annotation you can declare a fallback implementation of a client that will be picked up and used once all possible retries have been exhausted

Create @Fallback alternatives in the test classpath.

bookrecommendation/src/test/java/example/micronaut/BookInventoryClientStub.java

package example.micronaut;

import io.micronaut.context.annotation.Requires;
import io.micronaut.core.annotation.NonNull;
import io.micronaut.retry.annotation.Fallback;
import jakarta.inject.Singleton;
import reactor.core.publisher.Mono;

import jakarta.validation.constraints.NotBlank;

import static io.micronaut.context.env.Environment.TEST;

@Requires(env = TEST) (1)
@Fallback
@Singleton
public class BookInventoryClientStub implements BookInventoryOperations {

    @Override
    public Mono<Boolean> stock(@NonNull @NotBlank String isbn) {
        if (isbn.equals("1491950358")) {
            return Mono.just(true); (2)
        }
        if (isbn.equals("1680502395")) {
            return Mono.just(false); (3)
        }
        return Mono.empty(); (4)
    }
}

1	Make this fallback class to be effective only when the Micronaut environment TEST is active
2	Here we arbitrarily decided that if everything else fails, that book’s `stock` would be true
3	Similarly, we decided that other book’s `stock` method would be false
4	Finally, any other book will have their `stock` method return an empty value

bookrecommendation/src/test/java/example/micronaut/BookCatalogueClientStub.java

package example.micronaut;

import io.micronaut.context.annotation.Requires;
import io.micronaut.retry.annotation.Fallback;
import jakarta.inject.Singleton;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;

import static io.micronaut.context.env.Environment.TEST;

@Requires(env = TEST)
@Fallback
@Singleton
public class BookCatalogueClientStub implements BookCatalogueOperations {

    @Override
    public Publisher<Book> findAll() {
        Book buildingMicroservices = new Book("1491950358", "Building Microservices");
        Book releaseIt = new Book("1680502395", "Release It!");
        return Flux.just(buildingMicroservices, releaseIt);
    }
}

Write a test:

bookrecommendation/src/test/java/example/micronaut/BookControllerTest.java

package example.micronaut;

import io.micronaut.core.type.Argument;
import io.micronaut.http.HttpRequest;
import io.micronaut.http.client.HttpClient;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import jakarta.inject.Inject;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.condition.DisabledIfEnvironmentVariable;
import reactor.core.publisher.Flux;

import java.util.List;

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

@MicronautTest
public class BookControllerTest {

    @Inject
    @Client("/")
    HttpClient client;

    @DisabledIfEnvironmentVariable(named = "CI", matches = "true")
    @Test
    public void testRetrieveBooks() {
        List<BookRecommendation> books = client.toBlocking()
                .retrieve(HttpRequest.GET("/books"), Argument.listOf(BookRecommendation.class));
        assertEquals(1, books.size());
        assertEquals("Building Microservices", books.get(0).getName());
    }
}

Edit application.yml

bookrecommendation/src/main/resources/application.yml

micronaut:
  application:
    name: bookrecommendation (1)

1	Configure the application name. The name will be used later in the guide.

Modify the Application class to use dev as a default environment:

The Micronaut framework supports the concept of one or many default environments. A default environment is one that is only applied if no other environments are explicitly specified or deduced.

bookrecommendation/src/main/java/example/micronaut/Application.java

package example.micronaut;

import io.micronaut.runtime.Micronaut;

import static io.micronaut.context.env.Environment.DEVELOPMENT;

public class Application {

    public static void main(String[] args) {
        Micronaut.build(args)
                .mainClass(Application.class)
                .defaultEnvironments(DEVELOPMENT)
                .start();
    }
}

Create src/main/resources/application-dev.yml. The Micronaut framework applies this configuration file only for the dev environment.

bookrecommendation/src/main/resources/application-dev.yml

micronaut:
  server:
    port: 8080 (1)

1	Configure the application to listen on port 8080

Create a file named application-test.yml which is used in the test environment:

bookrecommendation/src/test/resources/application-test.yml

consul:
  client:
    registration:
      enabled: false

Run the unit test:

bookrecommendation

./mvnw test

4.4. Running the application

Run bookcatalogue microservice:

bookcatalogue

./mvnw mn:run

14:28:34.034 [main] INFO  io.micronaut.runtime.Micronaut - Startup completed in 499ms. Server Running: http://localhost:8081

Run bookinventory microservice:

bookinventory

./mvnw mn:run

14:31:13.104 [main] INFO  io.micronaut.runtime.Micronaut - Startup completed in 506ms. Server Running: http://localhost:8082

Run bookrecommendation microservice:

bookrecommendation

./mvnw mn:run

14:31:57.389 [main] INFO  io.micronaut.runtime.Micronaut - Startup completed in 523ms. Server Running: http://localhost:8080

You can run a cURL command to test the whole application:

curl http://localhost:8080/books

[{"name":"Building Microservices"}]

5. Consul and the Micronaut framework

5.1. Install Consul via Docker

The quickest way to start using Consul is via Docker:

docker run -p 8500:8500 consul

Alternatively you can install and run a local Consul instance.

The following screenshots show how to install/run Consul via Kitematic, a UI for Docker.

Configure ports:

5.2. Book Catalogue

Append to bookcatalogue service application.yml the following snippet:

bookcatalogue/src/main/resources/application.yml

consul:
  client:
    registration:
      enabled: true
    defaultZone: "${CONSUL_HOST:localhost}:${CONSUL_PORT:8500}"

This configuration registers a Micronaut application with Consul with minimal configuration. Discover a more complete list of configuration options at ConsulConfiguration.

5.3. Book Inventory

Modify the application.yml of the bookinventory application with the following snippet:

bookinventory/src/main/resources/application.yml

consul:
  client:
    registration:
      enabled: true
    defaultZone: "${CONSUL_HOST:localhost}:${CONSUL_PORT:8500}"

5.4. Book Recommendation

Append to bookrecommendation.application.yml the following snippet:

bookrecommendation/src/main/resources/application.yml

consul:
  client:
    registration:
      enabled: true
    defaultZone: "${CONSUL_HOST:localhost}:${CONSUL_PORT:8500}"

Modify BookInventoryClient and BookCatalogueClient to use the service id instead of a hardcoded URL.

bookrecommendation/src/main/java/example/micronaut/BookCatalogueClient.java

package example.micronaut;


import io.micronaut.http.annotation.Get;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.retry.annotation.Recoverable;
import org.reactivestreams.Publisher;

@Client(id = "bookcatalogue") (1)
@Recoverable(api = BookCatalogueOperations.class)

interface BookCatalogueClient extends BookCatalogueOperations {

    @Get("/books")
    Publisher<Book> findAll();
}

1	Use the configuration value `micronaut.application.name` used in `bookcatalogue` as service `id`.

bookrecommendation/src/main/java/example/micronaut/BookInventoryClient.java

package example.micronaut;


import io.micronaut.core.annotation.NonNull;
import io.micronaut.http.annotation.Consumes;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.retry.annotation.Recoverable;
import reactor.core.publisher.Mono;

import jakarta.validation.constraints.NotBlank;

import static io.micronaut.http.MediaType.TEXT_PLAIN;

@Client(id = "bookinventory") (1)
@Recoverable(api = BookInventoryOperations.class)

interface BookInventoryClient extends BookInventoryOperations {

    @Consumes(TEXT_PLAIN)
    @Get("/books/stock/{isbn}")
    Mono<Boolean> stock(@NonNull @NotBlank String isbn);
}

1	Use the configuration value `micronaut.application.name` used in `bookinventory` as service `id`.

5.5. Running the App

Run bookcatalogue microservice:

bookcatalogue

./gradlew run

14:28:34.034 [main] INFO  io.micronaut.runtime.Micronaut - Startup completed in 499ms. Server Running: http://localhost:8081
14:28:34.084 [nioEventLoopGroup-1-3] INFO  i.m.d.registration.AutoRegistration - Registered service [bookcatalogue] with Consul

Run bookinventory microservice:

bookinventory

./gradlew run

14:31:13.104 [main] INFO  io.micronaut.runtime.Micronaut - Startup completed in 506ms. Server Running: http://localhost:8082
14:31:13.154 [nioEventLoopGroup-1-3] INFO  i.m.d.registration.AutoRegistration - Registered service [bookinventory] with Consul

Run bookrecommendation microservice:

bookrecommendation

./gradlew run

14:31:57.389 [main] INFO  io.micronaut.runtime.Micronaut - Startup completed in 523ms. Server Running: http://localhost:8080
14:31:57.439 [nioEventLoopGroup-1-3] INFO  i.m.d.registration.AutoRegistration - Registered service [bookrecommendation] with Consul

Consul comes with a HTML UI. Open http://localhost:8500/ui in your browser.

You will see the services registered in Consul:

You can run a cURL command to test the whole application:

curl http://localhost:8080/books

[{"name":"Building Microservices"}]

6. Generate a Micronaut Application Native Executable with GraalVM

We will use GraalVM, an advanced JDK with ahead-of-time Native Image compilation, to generate a native executable of this Micronaut application.

Compiling Micronaut applications ahead of time with GraalVM significantly improves startup time and reduces the memory footprint of JVM-based applications.

Only Java and Kotlin projects support using GraalVM’s native-image tool. Groovy relies heavily on reflection, which is only partially supported by GraalVM.

6.1. GraalVM Installation

The easiest way to install GraalVM on Linux or Mac is to use SDKMan.io.

Java 21

sdk install java 21.0.5-graal

For installation on Windows, or for a manual installation on Linux or Mac, see the GraalVM Getting Started documentation.

The previous command installs Oracle GraalVM, which is free to use in production and free to redistribute, at no cost, under the GraalVM Free Terms and Conditions.

Alternatively, you can use the GraalVM Community Edition:

Java 21

sdk install java 21.0.2-graalce

6.2. Native Executable Generation

To generate a native executable using Maven, run:

./mvnw package -Dpackaging=native-image

The native executable is created in the target directory and can be run with target/micronautguide.

It is possible to customize the name of the native executable or pass additional build arguments using the Maven plugin for GraalVM Native Image building. Declare the plugin as following:

pom.xml

<plugin>
    <groupId>org.graalvm.buildtools</groupId>
    <artifactId>native-maven-plugin</artifactId>
    <version>0.10.3</version>
    <configuration>
        <!-- <1> -->
        <imageName>mn-graalvm-application</imageName> (1)
        <buildArgs>
              <!-- <2> -->
          <buildArg>-Ob</buildArg>
        </buildArgs>
    </configuration>
</plugin>

1	The native executable name will now be `mn-graalvm-application`.
2	It is possible to pass extra build arguments to `native-image`. For example, `-Ob` enables the quick build mode.

Start the native executables for the three microservices and run the same curl request as before to check that everything works with GraalVM.

7. Next Steps

Read more about Consul support in the Micronaut framework.

8. Help with the Micronaut Framework

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

9. 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…).

Table of Contents

Consul and the Micronaut Framework - Microservices Service Discovery

1. Getting Started

2. What you will need

3. Solution

4. Writing the App

4.1. Catalogue Microservice

4.2. Inventory Microservice

4.3. Recommendation Microservice

4.4. Running the application

5. Consul and the Micronaut framework

5.1. Install Consul via Docker

5.2. Book Catalogue

5.3. Book Inventory

5.4. Book Recommendation

5.5. Running the App

6. Generate a Micronaut Application Native Executable with GraalVM

6.1. GraalVM Installation

6.2. Native Executable Generation

7. Next Steps

8. Help with the Micronaut Framework

9. License