Kotlin / Gradle

Consul and the Micronaut Framework - Microservices Service Discovery

Use Consul service discovery to expose your Micronaut applications.

Sergio del Amo

On this guide

In this section

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.

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

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

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 an ISBN.
bookinventory - It exposes an endpoint to check whether a book has sufficient stock to fulfill an order. It uses a domain consisting of a stock level and an ISBN.
bookrecommendation - It consumes previous services and exposes an endpoint that recommends book names that are in stock.

Initially, we will hard-code the service addresses 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.

Note	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.

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=gradle --lang=kotlin

Note	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.

Note	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/kotlin/src/main/kotlin/example/micronaut/BooksController.kt

package example.micronaut

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

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

    @Get // 
    fun index(): List<Book> = listOf(
            Book("1491950358", "Building Microservices"),
            Book("1680502395", "Release It!"),
            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 with a List<Book>. Create the Book POJO:

bookcatalogue/kotlin/src/main/kotlin/example/micronaut/Book.kt

package example.micronaut

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

@Serdeable
data class Book(@NotBlank val isbn: String,
                @NotBlank val name: String)

Write a test:

bookcatalogue/kotlin/src/test/kotlin/example/micronaut/BooksControllerTest.kt

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.Assertions.assertEquals
import org.junit.jupiter.api.Assertions.assertTrue
import org.junit.jupiter.api.Test

@MicronautTest // 
class BooksControllerTest(@Client("/") val client: HttpClient) { // 

    @Test
    fun testRetrieveBooks() {
        val request: HttpRequest<*> = HttpRequest.GET<Any>("/books") // 
        val books = client.toBlocking().retrieve(request, Argument.listOf(Book::class.java)) // 

        assertEquals(3, books.size)
        assertTrue(books.contains(Book("1491950358", "Building Microservices")))
        assertTrue(books.contains(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	Easily parse JSON into Java objects.

Edit application.properties

bookcatalogue/src/main/resources/application.properties

micronaut.application.name=bookcatalogue

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

package example.micronaut

import io.micronaut.context.env.Environment.DEVELOPMENT
import io.micronaut.runtime.Micronaut.build

fun main(args: Array<String>) {
    build()
        .args(*args)
        .packages("example.micronaut")
        .defaultEnvironments(DEVELOPMENT)
        .start()
}

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

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

micronaut.server.port=8081

1	Configure the application to listen on port 8081.

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

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

consul.client.registration.enabled=false

Run the unit test:

bookcatalogue

./gradlew test

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=gradle --lang=kotlin

Note	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 bookinventory and a Micronaut application inside it with default package example.micronaut.

Note	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 Controller:

bookinventory/kotlin/src/main/kotlin/example/micronaut/BooksController.kt

package example.micronaut

import io.micronaut.http.MediaType.TEXT_PLAIN
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Produces
import java.util.Optional
import jakarta.validation.constraints.NotBlank

@Controller("/books") // 
open class BooksController {

    @Produces(TEXT_PLAIN) // 
    @Get("/stock/{isbn}") // 
    open fun stock(@NotBlank isbn: String): Boolean? =
        bookInventoryByIsbn(isbn).map { (_, stock) -> stock > 0 }.orElse(null)

    private fun bookInventoryByIsbn(isbn: String): Optional<BookInventory> {
        if (isbn == "1491950358") {
            return Optional.of(BookInventory(isbn, 4))
        }
        if (isbn == "1680502395") {
            return Optional.of(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/kotlin/src/main/kotlin/example/micronaut/BookInventory.kt

package example.micronaut

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

@Serdeable
data class BookInventory(@NotBlank val isbn: String,
                         val stock: Int)

Write a test:

bookinventory/kotlin/src/test/kotlin/example/micronaut/BooksControllerTest.kt

package example.micronaut

import io.micronaut.http.HttpRequest
import io.micronaut.http.HttpStatus.NOT_FOUND
import io.micronaut.http.HttpStatus.OK
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.Assertions.assertEquals
import org.junit.jupiter.api.Assertions.assertThrows
import org.junit.jupiter.api.Assertions.assertTrue
import org.junit.jupiter.api.Test

@MicronautTest
class BooksControllerTest(@Client("/") val httpClient: HttpClient) {

    @Test
    fun testBooksController() {
        val rsp = httpClient.toBlocking().exchange(
                HttpRequest.GET<Any>("/books/stock/1491950358"), Boolean::class.java)
        assertEquals(OK, rsp.status())
        assertTrue(rsp.body() == true)
    }

    @Test
    fun testBooksControllerWithNonExistingIsbn() {
        val thrown = assertThrows(HttpClientResponseException::class.java) {
            httpClient.toBlocking().exchange(HttpRequest.GET<Any>("/books/stock/XXXXX"), Boolean::class.java)
        }
        assertEquals(NOT_FOUND, thrown.response.status)
    }
}

Edit application.properties

bookinventory/src/main/resources/application.properties

micronaut.application.name=bookinventory

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

package example.micronaut

import io.micronaut.context.env.Environment.DEVELOPMENT
import io.micronaut.runtime.Micronaut.build

fun main(args: Array<String>) {
    build()
        .args(*args)
        .packages("example.micronaut")
        .defaultEnvironments(DEVELOPMENT)
        .start()
}

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

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

micronaut.server.port=8082

1	Configure the application to listen on port 8082.

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

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

consul.client.registration.enabled=false

Run the unit test:

bookinventory

./gradlew test

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=gradle --lang=kotlin

Note	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, reactor, and graalvm features.

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

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

bookrecommendation/kotlin/src/main/kotlin/example/micronaut/BookCatalogueOperations.kt

package example.micronaut

import org.reactivestreams.Publisher

interface BookCatalogueOperations {
    fun findAll(): Publisher<Book>
}

bookrecommendation/kotlin/src/main/kotlin/example/micronaut/BookCatalogueClient.kt

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") // 
@Recoverable(api = BookCatalogueOperations::class)

interface BookCatalogueClient : BookCatalogueOperations {

    @Get("/books")
    override fun findAll(): Publisher<Book>
}

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

package example.micronaut

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

@Serdeable
data class Book(@NotBlank val isbn: String,
                @NotBlank val name: String)

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

bookrecommendation/kotlin/src/main/kotlin/example/micronaut/BookInventoryOperations.kt

package example.micronaut

import reactor.core.publisher.Mono
import jakarta.validation.constraints.NotBlank

interface BookInventoryOperations {
    fun stock(@NotBlank isbn: String): Mono<Boolean>
}

bookrecommendation/kotlin/src/main/kotlin/example/micronaut/BookInventoryClient.kt

package example.micronaut

import io.micronaut.http.MediaType.TEXT_PLAIN
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

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

interface BookInventoryClient : BookInventoryOperations {

    @Consumes(TEXT_PLAIN)
    @Get("/books/stock/{isbn}")
    override fun stock(@NotBlank isbn: String): Mono<Boolean>
}

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

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") // 
class BookController(
        private val bookCatalogueOperations: BookCatalogueOperations,
        private val bookInventoryOperations: BookInventoryOperations) { // 

    @Get // 
    fun index(): Publisher<BookRecommendation> =

        Flux.from(bookCatalogueOperations.findAll())
                .flatMap { b ->
                    Flux.from(bookInventoryOperations.stock(b.isbn))
                            .filter { hasStock -> hasStock }
                            .map { b }
                }.map { (_, name) -> BookRecommendation(name) }
}

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

package example.micronaut

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

@Serdeable
data class BookRecommendation(@NotBlank val name: String)

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

package example.micronaut

import io.micronaut.context.annotation.Requires
import io.micronaut.context.env.Environment.TEST
import io.micronaut.retry.annotation.Fallback
import jakarta.inject.Singleton
import reactor.core.publisher.Mono
import jakarta.validation.constraints.NotBlank

@Requires(env = [TEST]) // 
@Fallback
@Singleton
open class BookInventoryClientStub : BookInventoryOperations {

    override fun stock(@NotBlank isbn: String): Mono<Boolean> {
        if (isbn == "1491950358") {
            return Mono.just(true) // 
        }
        if (isbn == "1680502395") {
            return Mono.just(false) // 
        }
        return Mono.empty() // 
    }
}

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

bookrecommendation/kotlin/src/test/kotlin/example/micronaut/BookCatalogueClientStub.kt

package example.micronaut

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

@Requires(env = [TEST])
@Fallback
@Singleton
class BookCatalogueClientStub : BookCatalogueOperations {

    override fun findAll(): Publisher<Book> {
        val buildingMicroservices = Book("1491950358", "Building Microservices")
        val releaseIt = Book("1680502395", "Release It!")
        return Flux.just(buildingMicroservices, releaseIt)
    }
}

Write a test:

bookrecommendation/kotlin/src/test/kotlin/example/micronaut/BookControllerTest.kt

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.Assertions.assertEquals
import org.junit.jupiter.api.Test
import org.junit.jupiter.api.condition.DisabledIfEnvironmentVariable

@MicronautTest
class BookControllerTest(@Client("/") val client: HttpClient) {

    @DisabledIfEnvironmentVariable(named = "CI", matches = "true")
    @Test
    fun testRetrieveBooks() {
        val books = client.toBlocking().retrieve(HttpRequest.GET<Any>("/books"),
            Argument.listOf(BookRecommendation::class.java))
        assertEquals(1, books.size)
        assertEquals("Building Microservices", books[0].name)
    }
}

Edit application.properties

bookrecommendation/src/main/resources/application.properties

micronaut.application.name=bookrecommendation

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

package example.micronaut

import io.micronaut.context.env.Environment.DEVELOPMENT
import io.micronaut.runtime.Micronaut.build

fun main(args: Array<String>) {
    build()
        .args(*args)
        .packages("example.micronaut")
        .defaultEnvironments(DEVELOPMENT)
        .start()
}

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

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

micronaut.server.port=8080

1	Configure the application to listen on port 8080

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

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

consul.client.registration.enabled=false

Run the unit test:

bookrecommendation

./gradlew test

Running the application

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

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

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

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

curl http://localhost:8080/books

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

Consul and the Micronaut framework

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:

Book Catalogue

Append the following snippet to the bookcatalogue service application.properties:

bookcatalogue/src/main/resources/application.properties

consul.client.registration.enabled=true
consul.client.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.

Book Inventory

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

bookinventory/src/main/resources/application.properties

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

Book Recommendation

Append the following snippet to the bookrecommendation service application.properties:

bookrecommendation/src/main/resources/application.properties

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

Modify BookInventoryClient and BookCatalogueClient to use the service id instead of a hard-coded URL.

bookrecommendation/kotlin/src/main/kotlin/example/micronaut/BookCatalogueClient.kt

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") // 
@Recoverable(api = BookCatalogueOperations::class)

interface BookCatalogueClient : BookCatalogueOperations {

    @Get("/books")
    override fun findAll(): Publisher<Book>
}

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

bookrecommendation/kotlin/src/main/kotlin/example/micronaut/BookInventoryClient.kt

package example.micronaut

import io.micronaut.http.MediaType.TEXT_PLAIN
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

@Client(id = "bookinventory") // 
@Recoverable(api = BookInventoryOperations::class)

interface BookInventoryClient : BookInventoryOperations {

    @Consumes(TEXT_PLAIN)
    @Get("/books/stock/{isbn}")
    override fun stock(@NotBlank isbn: String): Mono<Boolean>
}

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

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"}]

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.

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

GraalVM Installation

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

Java 25

sdk install java 25.0.2-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 25

sdk install java 25.0.2-graalce

Native Executable Generation

To generate a native executable using Gradle, run:

./gradlew nativeCompile

The native executable is created in build/native/nativeCompile directory and can be run with build/native/nativeCompile/micronautguide.

It is possible to customize the name of the native executable or pass additional parameters to GraalVM:

build.gradle

graalvmNative {
    binaries {
        main {
            imageName.set('mn-graalvm-application') // 
            buildArgs.add('-Ob') // 
        }
    }
}

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.

Next Steps

Read more about Consul support in the Micronaut framework.

Help with the Micronaut Framework

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

License

Note	All guides are released with an Apache License 2.0 for the code and a Creative Commons Attribution 4.0 license for the writing and media (images).