Kubernetes service discovery and distributed configuration

How to use Kubernetes service discovery and distributed configuration in a Micronaut application

Authors: Nemanja Mikic

Micronaut Version: 4.6.3

1. Getting Started

In this guide, we will create three microservices, build containerized versions and deploy them with Kubernetes. We will use Kubernetes Service discovery and Distributed configuration to wire up our microservices.

Kubernetes is a portable, extensible, open source platform for managing containerized workloads and services, that facilitates both declarative configuration and automation. It has a large, rapidly growing ecosystem. Kubernetes services, support, and tools are widely available.

You will discover how the Micronaut framework eases Kubernetes 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 17 or greater installed with JAVA_HOME configured appropriately
Docker.
Local Kubernetes cluster. We will use Minikube in this guide.

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 Apps

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

users - This microservice contains customers data that can place orders on items, also a new customer can be created. Microservice requires Basic authentication to access it.
orders - This microservice contains all orders that customers have created as well as available items that customers can order. Also this microservice enables the creation of new orders. Microservice requires Basic authentication to access it.
api - This microservice acts as a gateway to the orders and users services. It combines results from both services and checks data when customers create a new order.

Initially we will hard-code the URLs of the orders and users services in the api service. Additionally, we will hard-code credentials (username and password) into every microservice configuration that are required for Basic authentication.

In the second part of this guide we will use a Kubernetes discovery service and Kubernetes configuration maps to dynamically resolve the URLs of the orders and users microservices and get authentication credentials. The microservices call the Kubernetes API to register when they start up and then resolve placeholders inside the microservices' configurations.

4.1. Users Microservice

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

mn create-app          \
    --features=yaml,discovery-kubernetes,management,security,kubernetes,serialization-jackson,validation,graalvm \
    --build=maven             \
    --lang=kotlin               \
    --jdk=21              \
    example.micronaut.users

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 yaml, discovery-kubernetes, management, security, serialization-jackson, kubernetes and graalvm features.

The previous command creates a directory named users containing Micronaut application with a package named 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 package named controllers and create a UsersController class to handle incoming HTTP requests for the users microservice:

users/src/main/kotlin/example/micronaut/controllers/UsersController.kt

package example.micronaut.controllers

import example.micronaut.models.User
import io.micronaut.http.HttpStatus
import io.micronaut.http.annotation.Body
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Post
import io.micronaut.http.exceptions.HttpStatusException
import io.micronaut.security.annotation.Secured
import io.micronaut.security.rules.SecurityRule
import jakarta.validation.Valid
import jakarta.validation.constraints.NotNull
import kotlin.collections.ArrayList

@Controller("/users") (1)
@Secured(SecurityRule.IS_AUTHENTICATED) (2)
open class UsersController {
    var persons: MutableList<User?> = ArrayList()

    @Post (3)
    open fun add(@Body user: @Valid User?): User {
        val foundUser = findByUsername(user!!.username)
        if (foundUser != null) {
            throw HttpStatusException(HttpStatus.CONFLICT, "User with provided username already exists")
        }
        val newUser = User(persons.size + 1, user.firstName, user.lastName, user.username)
        persons.add(newUser)
        return newUser
    }

    @Get("/{id}") (4)
    open fun findById(id: @NotNull Int?): User? {
        return persons
            .firstOrNull { it: User? ->
                it!!.id == id
            }
    }

    @Get (5)
    open fun getUsers(): List<User?>? {
        return persons
    }

    open fun findByUsername(username: @NotNull String?): User? {
        return persons.firstOrNull { it: User? ->
            it!!.username == username
        }
    }
}

1	The class is defined as a controller with the @Controller annotation mapped to the path `/users`.
2	Annotate with `io.micronaut.security.Secured` to configure secured access. The `isAuthenticated()` expression will allow access only to authenticated users.
3	The @Post annotation maps the `add` method to an HTTP POST request on `/users`.
4	The @Get annotation maps the `findById` method to an HTTP GET request on `/users/{id}`.
5	The @Get annotation maps the `getUsers` method to an HTTP GET request on `/users`.

Create package named models where we will put our data beans.

The UsersController class uses a User object to represent customer. Create the User class

users/src/main/kotlin/example/micronaut/models/User.kt

package example.micronaut.models

import com.fasterxml.jackson.annotation.JsonProperty
import io.micronaut.core.annotation.Nullable
import io.micronaut.serde.annotation.Serdeable
import jakarta.validation.constraints.Max
import jakarta.validation.constraints.NotBlank

@Serdeable (1)
data class User(@Nullable @Max(10000) val id: Int, (2)
                @NotBlank @JsonProperty("first_name") val firstName:String,
                @NotBlank @JsonProperty("last_name")  val lastName:String,
                val username:String)

1	Declare the `@Serdeable` annotation at the type level in your source code to allow the type to be serialized or deserialized.
2	ID will be generated by application.

Create package named auth where you will check basic authentication credentials.

The Credentials class will load and store credentials (username and password) from a configuration file.

users/src/main/kotlin/example/micronaut/auth/Credentials.kt

package example.micronaut.auth

import io.micronaut.context.annotation.ConfigurationProperties

@ConfigurationProperties("authentication-credentials") (1)
class Credentials{
    lateinit var username: String
    lateinit var password: String
}

1	The `@ConfigurationProperties` annotation takes the configuration prefix.

The CredentialsChecker class, as the name suggests, will check if the provided credentials inside the HTTP request’s Authorization header are the same as those that are stored inside the Credentials class that we created above.

users/src/main/kotlin/example/micronaut/auth/CredentialsChecker.kt

package example.micronaut.auth

import io.micronaut.http.HttpRequest
import io.micronaut.security.authentication.AuthenticationFailureReason
import io.micronaut.security.authentication.AuthenticationRequest
import io.micronaut.security.authentication.AuthenticationResponse
import io.micronaut.security.authentication.provider.HttpRequestAuthenticationProvider
import jakarta.inject.Singleton

@Singleton (1)
class AuthenticationProviderUserPassword<B>(private val credentials: Credentials) : HttpRequestAuthenticationProvider<B> { (2)

    override fun authenticate(
        httpRequest: HttpRequest<B>?,
        authenticationRequest: AuthenticationRequest<String, String>
    ): AuthenticationResponse {
        return if (authenticationRequest.identity == credentials.username && authenticationRequest.secret == credentials.password)
            AuthenticationResponse.success(authenticationRequest.identity) else
            AuthenticationResponse.failure(AuthenticationFailureReason.CREDENTIALS_DO_NOT_MATCH)
    }
}

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

4.1.1. Write tests to verify application logic

Create the UsersClient, a declarative Micronaut HTTP Client for testing:

users/src/test/kotlin/example/micronaut/UsersClient.kt

package example.micronaut

import example.micronaut.models.User
import io.micronaut.http.annotation.Body
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Header
import io.micronaut.http.annotation.Post
import io.micronaut.http.client.annotation.Client

@Client("/") (1)
interface UsersClient {
    @Get("/users/{id}")
    fun getById(@Header authorization: String?, id: Int?): User?

    @Post("/users")
    fun createUser(@Header authorization: String?, @Body user: User?): User

    @Get("/users")
    fun getUsers(@Header authorization: String?): List<User?>
}

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.

HealthTest checks that there is /health endpoint that is required for service discovery.

users/src/test/kotlin/example/micronaut/HealthTest.kt

package example.micronaut

import io.micronaut.http.HttpRequest
import io.micronaut.http.HttpStatus
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

@MicronautTest (1)
class HealthTest {

    @Inject
    @field:Client("/")
    lateinit var client: HttpClient (2)

    @Test
    fun healthEndpointExposed() {
        val status = client.toBlocking().retrieve(
            HttpRequest.GET<Any>("/health"),
            HttpStatus::class.java
        )
        assertEquals(HttpStatus.OK, status)
    }
}

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.

UsersControllerTest tests endpoints inside the UserController.

users/src/test/kotlin/example/micronaut/UsersControllerTest.kt

package example.micronaut

import example.micronaut.auth.Credentials
import example.micronaut.models.User
import io.micronaut.http.HttpStatus
import io.micronaut.http.client.exceptions.HttpClientException
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.assertNotEquals
import org.junit.jupiter.api.Assertions.assertNotNull
import org.junit.jupiter.api.Assertions.assertNull
import org.junit.jupiter.api.Assertions.assertThrows
import org.junit.jupiter.api.Assertions.assertTrue
import org.junit.jupiter.api.Test
import java.util.Base64


@MicronautTest (1)
class UsersControllerTest {
    @Inject
    var usersClient: UsersClient? = null

    @Inject
    var credentials: Credentials? = null

    @Test
    fun testUnauthorized() {
        val exception = assertThrows(
            HttpClientException::class.java
        ) { usersClient!!.getUsers("") }
        assertTrue(exception.message!!.contains("Unauthorized"))
    }

    @Test
    fun userThatDoesntExists() {
        val authHeader = "Basic " + Base64.getEncoder()
            .encodeToString((credentials!!.username + ":" + credentials!!.password).toByteArray())
        val retriedUser = usersClient!!.getById(authHeader, 100)
        assertNull(retriedUser)
    }

    @Test
    fun multipleUserInteraction() {
        val authHeader = "Basic " + Base64.getEncoder()
            .encodeToString((credentials!!.username + ":" + credentials!!.password).toByteArray())
        val firstName = "firstName"
        val lastName = "lastName"
        val username = "username"
        val user = User(0, firstName, lastName, username)
        val createdUser = usersClient!!.createUser(authHeader, user)
        assertEquals(firstName, createdUser.firstName)
        assertEquals(lastName, createdUser.lastName)
        assertEquals(username, createdUser.username)
        assertNotNull(createdUser.id)
        val retriedUser = usersClient!!.getById(authHeader, createdUser.id)
        assertEquals(firstName, retriedUser!!.firstName)
        assertEquals(lastName, retriedUser.lastName)
        assertEquals(username, retriedUser.username)
        val users = usersClient!!.getUsers(authHeader)
        assertNotNull(users)
        assertNotNull(users.any {
            it!!.username == username
        })
    }

    @Test
    fun createSameUserTwice() {
        val authHeader = "Basic " + Base64.getEncoder()
            .encodeToString((credentials!!.username + ":" + credentials!!.password).toByteArray())
        val firstName = "SameUserFirstName"
        val lastName = "SameUserLastName"
        val username = "SameUserUsername"
        val user = User(0, firstName, lastName, username)
        val createdUser = usersClient!!.createUser(authHeader, user)
        assertEquals(firstName, createdUser.firstName)
        assertEquals(lastName, createdUser.lastName)
        assertEquals(username, createdUser.username)
        assertNotNull(createdUser.id)
        assertNotEquals(createdUser.id, 0)
        val exception = assertThrows(
            HttpClientResponseException::class.java
        ) { usersClient!!.createUser(authHeader, user) }
        assertEquals(HttpStatus.CONFLICT, exception.status)
        assertTrue(
            exception.response.getBody(String::class.java).orElse("")
                .contains("User with provided username already exists")
        )
    }
}

1	Annotate the class with `@MicronautTest` so the Micronaut framework will initialize the application context and the embedded server. More info.

Edit application.yml

users/src/main/resources/application.yml

micronaut:
  application:
    name: users
authentication-credentials:
  username: ${username} (1)
  password: ${password} (2)

1	Placeholder for username that will be populated by Kubernetes.
2	Placeholder for password that will be populated by Kubernetes.

Edit the bootstrap.yml file in the resources directory to enable distributed configuration. Change the default contents to the following:

users/src/main/resources/bootstrap.yml

micronaut:
  application:
    name: users
  config-client:
    enabled: true (1)
kubernetes:
  client:
    secrets:
      enabled: true (2)
      use-api: true (3)

1	Set `microanut.config-client.enabled: true` to read and resolve configuration from distributed sources.
2	Set `kubernetes.client.secrets.enabled: true` to enable Kubernetes secrets as distributed source.
3	Set `kubernetes.client.secrets.use-api: true` to use the Kubernetes API to fetch the configuration.

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

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

micronaut:
  server:
    port: 8081 (1)
authentication-credentials:
  username: "test_username" (2)
  password: "test_password" (3)

1	Configure the application to listen on port 8081.
2	Hardcoded username for the development environment.
3	Hardcoded password for the development environment.

Create a file named bootstrap-dev.yml to disable distributed configuration in the dev environment:

users/src/main/resources/bootstrap-dev.yml

kubernetes:
  client:
    secrets:
      enabled: false (1)

1	Disable the Kubernetes secrets client.

Create a file named application-test.yml for use in the test environment:

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

authentication-credentials:
  username: "test_username" (1)
  password: "test_password" (2)

1	Hardcoded username for the test environment.
2	Hardcoded password for the test environment.

Run the unit test:

users

./mvnw test

4.1.2. Running the application

Run the users microservice:

users

 MICRONAUT_ENVIRONMENTS=dev ./mvnw mn:run

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

4.2. Orders Microservice

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

mn create-app        \
  --features=yaml,discovery-kubernetes,management,security,kubernetes,serialization-jackson,validation,graalvm \
  --build=maven              \
  --lang=kotlin                \
  --jdk=21               \
example.micronaut.orders

The previous command creates a directory named orders containing a Micronaut application with a package named example.micronaut.

Diff

Create package named controllers and create the OrdersController and ItemsController classes to handle incoming HTTP requests to the orders microservice:

orders/src/main/kotlin/example/micronaut/controllers/OrdersController.kt

package example.micronaut.controllers

import example.micronaut.models.Item
import example.micronaut.models.Item.Companion.items
import example.micronaut.models.Order
import io.micronaut.http.HttpStatus
import io.micronaut.http.annotation.Body
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Post
import io.micronaut.http.exceptions.HttpStatusException
import io.micronaut.security.annotation.Secured
import io.micronaut.security.rules.SecurityRule
import java.math.BigDecimal
import jakarta.validation.Valid
import jakarta.validation.constraints.NotNull

@Controller("/orders") (1)
@Secured(SecurityRule.IS_AUTHENTICATED) (2)
open class OrdersController {

    private val orders: MutableList<Order> = ArrayList()

    @Get("/{id}") (3)
    open fun findById(id: @NotNull Int?): Order? {
        return orders.firstOrNull{ it: Order ->
            it.id == id
        }
    }

    @Get (4)
    fun getOrders(): List<Order?> {
        return orders
    }

    @Post (5)
    open fun createOrder(@Body order: @Valid Order): Order {
        if (order.itemIds.isNullOrEmpty()) {
            throw HttpStatusException(HttpStatus.BAD_REQUEST, "Items must be supplied")
        }
        val items: List<Item> = order.itemIds.map { x ->
            items.firstOrNull { y: Item ->
                y.id == x
            }?: throw HttpStatusException(HttpStatus.BAD_REQUEST, String.format("Item with id %s doesn't exist", x))
        }
        val total: BigDecimal = items.map(Item::price).reduce(BigDecimal::add)
        val newOrder = Order(orders.size + 1, order.userId, items, null, total)
        orders.add(newOrder)
        return newOrder
    }

}

1	The class is defined as a controller with the @Controller annotation mapped to the path `/orders`.
2	Annotate with `io.micronaut.security.Secured` to configure secured access. The `isAuthenticated()` expression will allow access only to authenticated users.
3	The @Get annotation maps the `findById` method to an HTTP GET request on `/orders/{id}`.
4	The @Get annotation maps the `getOrders` method to an HTTP GET request on `/orders`.
5	The @Post annotation maps the `createOrder` method to an HTTP POST request on `/orders`.

orders/src/main/kotlin/example/micronaut/controllers/ItemsController.kt

package example.micronaut.controllers

import example.micronaut.models.Item
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import io.micronaut.security.annotation.Secured
import io.micronaut.security.rules.SecurityRule
import jakarta.validation.constraints.NotNull

@Controller("/items") (1)
@Secured(SecurityRule.IS_AUTHENTICATED) (2)
open class ItemsController {

    @Get("/{id}") (3)
    open fun findById(id: @NotNull Int?): Item? {
        return Item.items
            .firstOrNull { it.id == id }
    }

    @Get (4)
    fun getItems(): List<Item?> {
        return Item.items
    }
}

1	The class is defined as a controller with the @Controller annotation mapped to the path `/items`.
2	Annotate with `io.micronaut.security.Secured` to configure secured access. The `isAuthenticated()` expression will allow access only to authenticated users.
3	The @Get annotation maps the `findById` method to an HTTP GET request on `/items/{id}`.
4	The @Get annotation maps the `getItems` method to an HTTP GET request on `/items`.

Create package named models where you will put your data beans.

The previous OrdersController and ItemsController controller uses Order and Item objects to represent customer orders. Create the Order class:

orders/src/main/kotlin/example/micronaut/models/Order.kt

package example.micronaut.models

import com.fasterxml.jackson.annotation.JsonProperty
import io.micronaut.core.annotation.Nullable
import io.micronaut.serde.annotation.Serdeable
import java.math.BigDecimal
import jakarta.validation.constraints.Max

@Serdeable (1)
data class Order (
    @Nullable @Max(10000) val id:Int, (2)
    @JsonProperty("user_id") val userId:Int,
    @Nullable val items: List<Item>?, (3)
    @JsonProperty("item_ids") val itemIds:List<Int>?, (4)
    @Nullable val total: BigDecimal?)

1	Declare the `@Serdeable` annotation at the type level in your source code to allow the type to be serialized or deserialized.
2	ID will be generated by application.
3	The `List` of `Item` class will be populated by the server and will be only visible in sever responses.
4	List of item_ids will be provided by client requests.

Create the Item class:

orders/src/main/kotlin/example/micronaut/models/Item.kt

package example.micronaut.models

import com.fasterxml.jackson.annotation.JsonProperty
import io.micronaut.serde.annotation.Serdeable
import java.math.BigDecimal

@Serdeable (1)
data class Item (
    val id:Int,
    val name:String,
    val price: BigDecimal
) {
    companion object {
        var items: List<Item> = listOf(
            Item(1, "Banana", BigDecimal("1.5")),
            Item(2, "Kiwi", BigDecimal("2.5")),
            Item(3, "Grape", BigDecimal("1.25"))
        )
    }
}

1	Declare the `@Serdeable` annotation at the type level in your source code to allow the type to be serialized or deserialized.

Create package named auth where you will check basic authentication credentials.

The Credentials class will load and store credentials (username and password) from configuration files.

orders/src/main/kotlin/example/micronaut/auth/Credentials.kt

package example.micronaut.auth

import io.micronaut.context.annotation.ConfigurationProperties

@ConfigurationProperties("authentication-credentials") (1)
class Credentials{
    lateinit var username: String
    lateinit var password: String
}

1	The `@ConfigurationProperties` annotation takes the configuration prefix.

The CredentialsChecker class, as name suggests, will check if provided credentials inside an HTTP request’s Authorization header are the same as those that are stored inside Credentials class that we created above.

orders/src/main/kotlin/example/micronaut/auth/CredentialsChecker.kt

package example.micronaut.auth

import io.micronaut.http.HttpRequest
import io.micronaut.security.authentication.AuthenticationFailureReason
import io.micronaut.security.authentication.AuthenticationRequest
import io.micronaut.security.authentication.AuthenticationResponse
import io.micronaut.security.authentication.provider.HttpRequestAuthenticationProvider
import jakarta.inject.Singleton

@Singleton (1)
class AuthenticationProviderUserPassword<B>(private val credentials: Credentials) : HttpRequestAuthenticationProvider<B> { (2)

    override fun authenticate(
        httpRequest: HttpRequest<B>?,
        authenticationRequest: AuthenticationRequest<String, String>
    ): AuthenticationResponse {
        return if (authenticationRequest.identity == credentials.username && authenticationRequest.secret == credentials.password)
            AuthenticationResponse.success(authenticationRequest.identity) else
            AuthenticationResponse.failure(AuthenticationFailureReason.CREDENTIALS_DO_NOT_MATCH)
    }
}

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

4.2.1. Write tests to verify application logic

Create the OrderItemClient, a declarative Micronaut HTTP Client for testing:

orders/src/test/kotlin/example/micronaut/OrderItemClient.kt

package example.micronaut

import example.micronaut.models.Item
import example.micronaut.models.Order
import io.micronaut.http.annotation.Body
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Header
import io.micronaut.http.annotation.Post
import io.micronaut.http.client.annotation.Client

@Client("/") (1)
interface OrderItemClient {
    @Get("/orders/{id}")
    fun getOrderById(@Header authorization: String?, id: Int?): Order?

    @Post("/orders")
    fun createOrder(@Header authorization: String?, @Body order: Order?): Order

    @Get("/orders")
    fun getOrders(@Header authorization: String?): List<Order>

    @Get("/items")
    fun getItems(@Header authorization: String?): List<Item>

    @Get("/items/{id}")
    fun getItemsById(@Header authorization: String?, id: Int?): Item?
}

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.

HealthTest checks that there is /health endpoint that is required for service discovery.

orders/src/test/kotlin/example/micronaut/HealthTest.kt

package example.micronaut

import io.micronaut.http.HttpRequest
import io.micronaut.http.HttpStatus
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

@MicronautTest (1)
class HealthTest {

    @Inject
    @field:Client("/")
    lateinit var client: HttpClient (2)

    @Test
    fun healthEndpointExposed() {
        val status = client.toBlocking().retrieve(
            HttpRequest.GET<Any>("/health"),
            HttpStatus::class.java
        )
        assertEquals(HttpStatus.OK, status)
    }
}

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.

ItemsControllerTest tests endpoints inside the ItemController.

orders/src/test/kotlin/example/micronaut/ItemsControllerTest.kt

package example.micronaut

import example.micronaut.auth.Credentials
import example.micronaut.models.Item
import io.micronaut.http.client.exceptions.HttpClientException
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.assertNotNull
import org.junit.jupiter.api.Assertions.assertThrows
import org.junit.jupiter.api.Assertions.assertTrue
import org.junit.jupiter.api.Test
import java.math.BigDecimal
import java.util.Base64

@MicronautTest (1)
class ItemsControllerTest {
    @Inject
    var orderItemClient: OrderItemClient? = null

    @Inject
    var credentials: Credentials? = null

    @Test
    fun testUnauthorized() {
        val exception = assertThrows(
            HttpClientException::class.java
        ) { orderItemClient?.getItems("") }
        assertTrue(exception.message!!.contains("Unauthorized"))
    }

    @Test
    fun getItem() {
        val itemId = 1
        val authHeader = "Basic " + Base64.getEncoder()
            .encodeToString((credentials!!.username + ":" + credentials!!.password).toByteArray())
        val item: Item? = orderItemClient!!.getItemsById(authHeader, itemId)
        assertEquals(itemId, item!!.id)
        assertEquals("Banana", item.name)
        assertEquals(BigDecimal("1.5"), item.price)
    }

    @Test
    fun getItems() {
        val authHeader = "Basic " + Base64.getEncoder()
            .encodeToString((credentials!!.username + ":" + credentials!!.password).toByteArray())
        val items: List<Item> = orderItemClient!!.getItems(authHeader)
        assertNotNull(items)
        val existingItemNames = listOf("Kiwi", "Banana", "Grape")
        assertEquals(3, items.size)
        assertTrue(items.stream()
            .map<Any>(Item::name)
            .allMatch { name: Any ->
                existingItemNames.stream().anyMatch { x: String -> x == name }
            })
    }
}

1	Annotate the class with `@MicronautTest` so the Micronaut framework will initialize the application context and the embedded server. More info.

OrdersControllerTest tests endpoints inside the OrdersController.

orders/src/test/kotlin/example/micronaut/OrdersControllerTest.kt

package example.micronaut

import example.micronaut.auth.Credentials
import example.micronaut.models.Order
import io.micronaut.http.HttpStatus
import io.micronaut.http.client.exceptions.HttpClientException
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
import org.junit.jupiter.api.Assertions.assertEquals
import org.junit.jupiter.api.Assertions.assertNotNull
import org.junit.jupiter.api.Assertions.assertTrue
import org.junit.jupiter.api.Test
import java.math.BigDecimal
import java.util.Base64

@MicronautTest (1)
class OrdersControllerTest {

    @Inject
    var orderItemClient: OrderItemClient? = null

    @Inject
    var credentials: Credentials? = null

    @Test
    fun testUnauthorized() {
        val exception = Assertions.assertThrows(
            HttpClientException::class.java
        ) { orderItemClient!!.getOrders("") }
        assertTrue(exception.message!!.contains("Unauthorized"))
    }

    @Test
    fun multipleOrderInteraction() {
        val authHeader = "Basic " + Base64.getEncoder()
            .encodeToString((credentials!!.username + ":" + credentials!!.password).toByteArray())
        val userId = 1
        val itemIds = listOf(1, 1, 2, 3)
        val order = Order(0, userId, null, itemIds, null)
        val createdOrder = orderItemClient!!.createOrder(authHeader, order)
        assertNotNull(createdOrder.items)
        assertEquals(4, createdOrder.items!!.size)
        assertEquals(BigDecimal("6.75"), createdOrder.total)
        assertEquals(userId, createdOrder.userId)
        val retrievedOrder = orderItemClient!!.getOrderById(authHeader, createdOrder.id)
        assertNotNull(retrievedOrder!!.items)
        assertEquals(4, retrievedOrder.items!!.size)
        assertEquals(BigDecimal("6.75"), retrievedOrder.total)
        assertEquals(userId, retrievedOrder.userId)
        val orders = orderItemClient!!.getOrders(authHeader)
        assertNotNull(orders)
        assertTrue(orders.stream()
            .map<Any>(Order::userId)
            .anyMatch { id: Any -> id == userId })
    }

    @Test
    fun itemDoesntExists() {
        val authHeader = "Basic " + Base64.getEncoder()
            .encodeToString((credentials!!.username + ":" + credentials!!.password).toByteArray())
        val userId = 1
        val itemIds = listOf(5)
        val order = Order(0, userId, null, itemIds, null)
        val exception = Assertions.assertThrows(
            HttpClientResponseException::class.java
        ) { orderItemClient!!.createOrder(authHeader, order) }
        assertEquals(exception.status, HttpStatus.BAD_REQUEST)
        assertTrue(
            exception.response.getBody(String::class.java).orElse("").contains("Item with id 5 doesn't exist")
        )
    }

    @Test
    fun orderEmptyItems() {
        val authHeader = "Basic " + Base64.getEncoder()
            .encodeToString((credentials!!.username + ":" + credentials!!.password).toByteArray())
        val userId = 1
        val order = Order(0, userId, null, null, null)
        val exception = Assertions.assertThrows(
            HttpClientResponseException::class.java
        ) { orderItemClient!!.createOrder(authHeader, order) }
        assertEquals(exception.status, HttpStatus.BAD_REQUEST)
        assertTrue(
            exception.response.getBody(String::class.java).orElse("").contains("Items must be supplied")
        )
    }
}

1	Annotate the class with `@MicronautTest` so the Micronaut framework will initialize the application context and the embedded server. More info.

Edit application.yml so it contains:

orders/src/main/resources/application.yml

micronaut:
  application:
    name: orders
authentication-credentials:
  username: ${username} (1)
  password: ${password} (2)

1	Placeholder for username that will be populated by Kubernetes.
2	Placeholder for password that will be populated by Kubernetes.

Edit bootstrap.yml file in the resources directory to enable distributed configuration. Change it to the following:

orders/src/main/resources/bootstrap.yml

micronaut:
  application:
    name: orders
  config-client:
    enabled: true (1)
kubernetes:
  client:
    secrets:
      enabled: true (2)
      use-api: true (3)

1	Set `microanut.config-client.enabled: true` to read and resolve configuration from distributed sources.
2	Set `kubernetes.client.secrets.enabled: true` to enable Kubernetes secrets as distributed source.
3	Set `kubernetes.client.secrets.use-api: true` to use Kubernetes API to fetch configuration.

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

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

micronaut:
  server:
    port: 8082 (1)
authentication-credentials:
  username: "test_username" (2)
  password: "test_password" (3)

1	Configure the application to listen on port 8082.
2	Hardcoded username for development environment.
3	Hardcoded password for development environment.

Create a file named bootstrap-dev.yml to disable distributed configuration in the dev environment:

orders/src/main/resources/bootstrap-dev.yml

kubernetes:
  client:
    secrets:
      enabled: false (1)

1	Disable Kubernetes secrets client.

Create a file named application-test.yml to be used in the test environment:

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

micronaut:
  application:
    name: orders
authentication-credentials:
  username: "test_username" (1)
  password: "test_password" (2)

1	Hardcoded username for development environment.
2	Hardcoded password for development environment.

Run the unit test:

orders

./mvnw test

4.2.2. Running the application

Run the orders microservice:

orders

MICRONAUT_ENVIRONMENTS=dev ./mvnw mn:run

14:28:34.034 [main] INFO  io.micronaut.runtime.Micronaut - Startup completed in 499ms. Server Running: http://localhost:8082

4.3. API (Gateway) Microservice

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

mn create-app         \
   --features=yaml,discovery-kubernetes,management,kubernetes,serialization-jackson,http-client,mockito,kapt,graalvm \
   --build=maven           \
   --lang=kotlin             \
   --jdk=21            \
    example.micronaut.api

If you use Micronaut Launch, select Micronaut Application as application type and add the yaml, discovery-kubernetes, management, kubernetes, serialization-jackson, mockito, graalvm and http-client features.

The previous command creates a directory named api containing a Micronaut application with a package named example.micronaut.

Diff

Create a package named controllers and create a GatewayController class to handle incoming HTTP requests to the api microservice:

api/src/main/kotlin/example/micronaut/controllers/GatewayController.kt

package example.micronaut.controllers

import example.micronaut.clients.OrdersClient
import example.micronaut.clients.UsersClient
import example.micronaut.models.Item
import example.micronaut.models.Order
import example.micronaut.models.User
import io.micronaut.core.annotation.NonNull
import io.micronaut.http.HttpStatus
import io.micronaut.http.annotation.Body
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Post
import io.micronaut.http.exceptions.HttpStatusException
import io.micronaut.scheduling.TaskExecutors
import io.micronaut.scheduling.annotation.ExecuteOn
import reactor.core.publisher.Flux
import reactor.core.publisher.Mono
import reactor.core.scheduler.Schedulers
import jakarta.validation.Valid

@Controller("/api") (1)
@ExecuteOn(TaskExecutors.BLOCKING) (2)
class GatewayController(ordersClient: OrdersClient, usersClient: UsersClient) {

    private val ordersClient: OrdersClient
    private val userClient: UsersClient

    init {
        this.ordersClient = ordersClient
        this.userClient = usersClient
    }


    @Get("/users/{id}") (3)
    fun getUserById(@NonNull id: Int): User? {
        return userClient.getById(id)
    }

    @Get("/orders/{id}") (4)
    fun getOrdersById(@NonNull id: Int): Order {
        val order = ordersClient.getOrderById(id)

        return Order(
            order.id,
            null,
            getUserById(order.userId!!),
            order.items,
            order.itemIds,
            order.total
        )
    }

    @Get("/items/{id}") (5)
    fun getItemsById(@NonNull id: Int): Item {
        return ordersClient.getItemsById(id)
    }

    @Get("/users") (6)
    fun getUsers(): List<User> {
        return userClient.users
    }

    @Get("/items") (7)
    fun getItems(): List<Item> {
        return ordersClient.items
    }

    @Get("/orders") (8)
    fun getOrders(): List<Order>? {
        val orders = mutableListOf<Order>()
        ordersClient.orders.forEach{orders.add(Order(
            it.id,
            null,
            getUserById(it.userId!!),
            it.items,
            it.itemIds,
            it.total))
        }
        return orders
    }

    @Post("/orders") (9)
    fun createOrder(@Body order: @Valid Order): Order? {
        val user = getUserById(order!!.userId!!)
            ?: throw  HttpStatusException(
                HttpStatus.BAD_REQUEST,
                String.format("User with id %s doesn't exist", order.userId)
            )

        val createdOrder = ordersClient.createOrder(order)

        return Order(
            createdOrder!!.id,
            null,
            user,
            createdOrder.items,
            createdOrder.itemIds,
            createdOrder.total
        )
    }

    @Post("/users") (10)
    fun createUser(@Body @NonNull user: User): User {
        return userClient.createUser(user)
    }
}

1	The class is defined as a controller with the @Controller annotation mapped to the path `/api`.
2	It is critical that any blocking I/O operations (such as fetching the data from the database) are offloaded to a separate thread pool that does not block the Event loop.
3	The @Get annotation maps the `getUserById` method to an HTTP GET request on `/users/{id}`.
4	The @Get annotation maps the `getOrdersById` method to an HTTP GET request on `/orders/{id}`.
5	The @Get annotation maps the `getItemsById` method to an HTTP GET request on `/items/{id}`.
6	The @Get annotation maps the `getUsers` method to an HTTP GET request on `/users`.
7	The @Get annotation maps the `getItems` method to an HTTP GET request on `/items`.
8	The @Get annotation maps the `getOrders` method to an HTTP GET request on `/orders`.
9	The @Post annotation maps the `createUser` method to an HTTP POST request on `/users`.
10	The @Post annotation maps the `createOrder` method to an HTTP POST request on `/orders`.

Create package named models where you will put your data beans.

The previous GatewayController and ItemsController controller uses User, Order and Item to represent customer orders. Create the User class:

api/src/main/kotlin/example/micronaut/models/User.kt

package example.micronaut.models

import com.fasterxml.jackson.annotation.JsonProperty
import io.micronaut.core.annotation.Nullable
import io.micronaut.serde.annotation.Serdeable
import jakarta.validation.constraints.Max
import jakarta.validation.constraints.NotBlank

@Serdeable (1)
data class User(@Nullable @Max(10000) val id: Int, (1)
                @NotBlank @JsonProperty("first_name") val firstName:String,
                @NotBlank @JsonProperty("last_name")  val lastName:String,
                val username:String)

1	Declare the `@Serdeable` annotation at the type level in your source code to allow the type to be serialized or deserialized.

Create the Order class:

api/src/main/kotlin/example/micronaut/models/Order.kt

package example.micronaut.models

import com.fasterxml.jackson.annotation.JsonProperty
import io.micronaut.core.annotation.Nullable
import io.micronaut.serde.annotation.Serdeable
import java.math.BigDecimal
import jakarta.validation.constraints.Max
import jakarta.validation.constraints.NotBlank

@Serdeable (1)
data class Order (
    @Nullable @Max(10000) val id:Int, (2)
    @NotBlank @Nullable @JsonProperty("user_id") val userId:Int?,
    @Nullable val user: User?,
    val items: List<Item>?, (3)
    @NotBlank @JsonProperty("item_ids") val itemIds:List<Int>?, (4)
    val total: BigDecimal?)

1	Declare the `@Serdeable` annotation at the type level in your source code to allow the type to be serialized or deserialized.

Create the Item class:

api/src/main/kotlin/example/micronaut/models/Item.kt

package example.micronaut.models

import com.fasterxml.jackson.annotation.JsonProperty
import io.micronaut.serde.annotation.Serdeable
import java.math.BigDecimal

@Serdeable (1)
data class Item (
    val id:Int,
    val name:String,
    val price: BigDecimal
) {
    companion object {
        var items: List<Item> = listOf(
            Item(1, "Banana", BigDecimal("1.5")),
            Item(2, "Kiwi", BigDecimal("2.5")),
            Item(3, "Grape", BigDecimal("1.25"))
        )
    }
}

1	Declare the `@Serdeable` annotation at the type level in your source code to allow the type to be serialized or deserialized.

Create a package named clients where you will put the HTTP Clients to call the users and orders microservices.

Create a UsersClient for the users microservice.

api/src/main/kotlin/example/micronaut/clients/UsersClient.kt

package example.micronaut.clients

import example.micronaut.models.User
import io.micronaut.http.annotation.Body
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Post
import io.micronaut.http.client.annotation.Client
import reactor.core.publisher.Flux
import reactor.core.publisher.Mono

@Client("users") (1)
interface UsersClient {
    @Get("/users/{id}")
    fun getById(id: Int): User

    @Post("/users")
    fun createUser(@Body user: User?): User

    @get:Get("/users")
    val users: List<User>
}

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 an OrdersClient for the orders microservice.

api/src/main/kotlin/example/micronaut/clients/OrdersClient.kt

package example.micronaut.clients

import example.micronaut.models.Item
import example.micronaut.models.Order
import io.micronaut.http.annotation.Body
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Post
import io.micronaut.http.client.annotation.Client
import reactor.core.publisher.Flux
import reactor.core.publisher.Mono

@Client("orders") (1)
interface OrdersClient {
    @Get("/orders/{id}")
    fun getOrderById(id: Int): Order

    @Post("/orders")
    fun createOrder(@Body order: Order?): Order

    @get:Get("/orders")
    val orders: List<Order>

    @get:Get("/items")
    val items: List<Item>

    @Get("/items/{id}")
    fun getItemsById(id: Int): Item
}

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 package named auth where we will check basic authentication credentials.

Create a Credentials class that will load the username and password from configuration that will be needed for comparison.

api/src/main/kotlin/example/micronaut/auth/Credentials.kt

package example.micronaut.auth

import io.micronaut.context.annotation.ConfigurationProperties

@ConfigurationProperties("authentication-credentials") (1)
class Credentials{
    lateinit var username: String
    lateinit var password: String
}

1	The `@ConfigurationProperties` annotation takes the configuration prefix.

Create an AuthClientFilter class that is a client filter applied to every client. It adds basic authentication header with credentials that are stored in the Credentials class.

api/src/main/kotlin/example/micronaut/auth/AuthClientFilter.kt

package example.micronaut.auth

import io.micronaut.http.HttpResponse
import io.micronaut.http.MutableHttpRequest
import io.micronaut.http.annotation.Filter
import io.micronaut.http.filter.ClientFilterChain
import io.micronaut.http.filter.HttpClientFilter
import org.reactivestreams.Publisher

@Filter(Filter.MATCH_ALL_PATTERN)
class AuthClientFilter(credentials: Credentials) : HttpClientFilter {
    private val credentials: Credentials

    init {
        this.credentials = credentials
    }

    override fun doFilter(request: MutableHttpRequest<*>, chain: ClientFilterChain): Publisher<out HttpResponse<*>?> {
        return chain.proceed(request.basicAuth(credentials.username, credentials.password))
    }
}

Create a class named ErrorExceptionHandler in the example.micronaut package. ErrorExceptionHandler will propagate errors from the orders and users microservices.

api/src/main/kotlin/example/micronaut/ErrorExceptionHandler.kt

package example.micronaut

import io.micronaut.http.HttpRequest
import io.micronaut.http.HttpResponse
import io.micronaut.http.client.exceptions.HttpClientResponseException
import io.micronaut.http.server.exceptions.ExceptionHandler
import jakarta.inject.Singleton

@Singleton (1)
class ErrorExceptionHandler :
    ExceptionHandler<HttpClientResponseException, HttpResponse<*>> {
    override fun handle(request: HttpRequest<*>?, exception: HttpClientResponseException): HttpResponse<*> {
        return HttpResponse.status<Any>(exception.response.status()).body(
            exception.response.getBody(
                String::class.java
            ).orElse(null)
        )
    }
}

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

4.3.1. Write tests to verify application logic

Create a GatewayClient, a declarative Micronaut HTTP Client for testing:

api/src/test/kotlin/example/micronaut/GatewayClient.kt

package example.micronaut

import example.micronaut.models.Item
import example.micronaut.models.Order
import example.micronaut.models.User
import io.micronaut.http.annotation.Body
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Post
import io.micronaut.http.client.annotation.Client

@Client("/") (1)
interface GatewayClient {
    @Get("/api/items/{id}")
    fun getItemById(id: Int?): Item?

    @Get("/api/orders/{id}")
    fun getOrderById(id: Int?): Order?

    @Get("/api/users/{id}")
    fun getUsersById(id: Int?): User?

    @get:Get("/api/users")
    val users: List<User>

    @get:Get("/api/items")
    val items: List<Item>

    @get:Get("/api/orders")
    val orders: List<Order>

    @Post("/api/orders")
    fun createOrder(@Body order: Order): Order

    @Post("/api/users")
    fun createUser(@Body user: User): User
}

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.

HealthTest checks that there is /health endpoint that is required for service discovery.

api/src/test/kotlin/example/micronaut/HealthTest.kt

package example.micronaut

import io.micronaut.http.HttpRequest
import io.micronaut.http.HttpStatus
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

@MicronautTest (1)
class HealthTest {

    @Inject
    @field:Client("/")
    lateinit var client: HttpClient (2)

    @Test
    fun healthEndpointExposed() {
        val status = client.toBlocking().retrieve(
            HttpRequest.GET<Any>("/health"),
            HttpStatus::class.java
        )
        assertEquals(HttpStatus.OK, status)
    }
}

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.

GatewayControllerTest tests endpoints inside the GatewayController.

api/src/test/kotlin/example/micronaut/GatewayControllerTest.kt

package example.micronaut

import example.micronaut.clients.OrdersClient
import example.micronaut.clients.UsersClient
import example.micronaut.models.Item
import example.micronaut.models.Order
import example.micronaut.models.User
import io.micronaut.http.HttpResponse
import io.micronaut.http.HttpStatus
import io.micronaut.http.client.exceptions.HttpClientResponseException
import io.micronaut.test.annotation.MockBean
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.assertNotNull
import org.junit.jupiter.api.Assertions.assertNull
import org.junit.jupiter.api.Assertions.assertThrows
import org.junit.jupiter.api.Assertions.assertTrue
import org.junit.jupiter.api.Test
import org.mockito.ArgumentMatchers.any
import org.mockito.Mockito.mock
import org.mockito.Mockito.`when`
import java.math.BigDecimal

@MicronautTest (1)
class GatewayControllerTest {
    @Inject
    var ordersClient: OrdersClient? = null

    @Inject
    var usersClient: UsersClient? = null

    @Inject
    var gatewayClient: GatewayClient? = null

    @MockBean(OrdersClient::class)
    fun ordersClient(): OrdersClient {
        return mock(OrdersClient::class.java)
    }

    @MockBean(UsersClient::class)
    fun usersClient(): UsersClient {
        return mock(UsersClient::class.java)
    }

    @Test
    fun itemById() {
        val itemId = 1
        val item = Item(itemId, "test", BigDecimal.ONE)
        `when`(ordersClient!!.getItemsById(1)).thenReturn(item)
        val retrievedItem = gatewayClient!!.getItemById(item.id)
        assertEquals(item.id, retrievedItem!!.id)
        assertEquals(item.name, retrievedItem.name)
        assertEquals(item.price, retrievedItem.price)
    }

    @Test
    fun orderById() {
        val order = Order(1, 2, null, null, ArrayList(), null)
        val user = User(order.userId!!, "firstName", "lastName", "test")
        `when`(ordersClient!!.getOrderById(1)).thenReturn(order)
        `when`(usersClient!!.getById(user.id)).thenReturn(user)
        val retrievedOrder = gatewayClient!!.getOrderById(order.id)
        assertEquals(order.id, retrievedOrder!!.id)
        assertEquals(order.userId, retrievedOrder.user!!.id)
        assertNull(retrievedOrder.userId)
        assertEquals(user.username, retrievedOrder.user!!.username)
    }

    @Test
    fun userById() {
        val user = User(1, "firstName", "lastName", "test")
        `when`(usersClient!!.getById(1)).thenReturn(user)
        val retrievedUser = gatewayClient!!.getUsersById(user.id)
        assertEquals(user.id, retrievedUser!!.id)
        assertEquals(user.username, retrievedUser.username)
    }

    @Test
    fun users() {
        val user = User(1, "firstName", "lastName", "test")
        `when`(usersClient!!.users).thenReturn(listOf(user))
        val users = gatewayClient!!.users
        assertNotNull(users)
        assertEquals(1, users.size)
        assertEquals(user.id, users[0].id)
        assertEquals(user.username, users[0].username)
    }

    @Test
    fun items() {
        val item = Item(1, "test", BigDecimal.ONE)
        `when`(ordersClient!!.items).thenReturn(listOf(item))
        val items = gatewayClient!!.items
        assertNotNull(items)
        assertEquals(1, items.size)
        assertEquals(item.name, items[0].name)
        assertEquals(item.price, items[0].price)
    }

    @Test
    fun orders() {
        val order = Order(1, 2, null, null, ArrayList(), null)
        val user = User(order.userId!!, "firstName", "lastName", "test")
        `when`(ordersClient!!.orders).thenReturn(listOf(order))
        `when`(usersClient!!.getById(order.userId!!)).thenReturn(user)
        val orders = gatewayClient!!.orders
        assertNotNull(orders)
        assertEquals(1, orders.size)
        assertNull(orders[0].userId)
        assertEquals(user.id, orders[0].user!!.id)
        assertEquals(order.id, orders[0].id)
        assertEquals(user.username, orders[0].user!!.username)
    }

    @Test
    fun createUser() {
        val firstName = "firstName"
        val lastName = "lastName"
        val username = "username"
        val user = User(0, firstName, lastName, username)
        `when`(usersClient!!.createUser(user)).thenReturn(user)
        val createdUser = gatewayClient!!.createUser(user)
        assertEquals(firstName, createdUser.firstName)
        assertEquals(lastName, createdUser.lastName)
        assertEquals(username, createdUser.username)
    }

    @Test
    fun createOrder() {
        val order = Order(1, 2, null, null, null, null)
        val user = User(order.userId!!, "firstName", "lastName", "test")
        `when`(usersClient!!.getById(user.id)).thenReturn(user)
        `when`(ordersClient!!.createOrder(order)).thenReturn(order)
        val createdOrder = gatewayClient!!.createOrder(order)
        assertEquals(order.id, createdOrder.id)
        assertNull(createdOrder.userId)
        assertEquals(order.userId, createdOrder.user!!.id)
        assertEquals(user.username, createdOrder.user!!.username)
    }

    @Test
    fun createOrderUserDoesntExists() {
        val order = Order(1, 2, null, null, null, BigDecimal(0))
        `when`(ordersClient!!.createOrder(order)).thenReturn(order)
        `when`(usersClient!!.getById(order.userId!!)).thenReturn(null)
        val exception = assertThrows(
            HttpClientResponseException::class.java
        ) { gatewayClient!!.createOrder(order) }
        assertEquals(exception.status, HttpStatus.BAD_REQUEST)
        assertTrue(
            exception.response.getBody(String::class.java).orElse("").contains("User with id 2 doesn't exist")
        )
    }

    @Test
    fun exceptionHandler() {
        val user = User(1, "firstname", "lastname", "username")
        val message = "Test error message"
        `when`(usersClient!!.createUser(user)).thenThrow(
            HttpClientResponseException(
                "Test",
                HttpResponse.badRequest(message)
            )
        )
        val exception = assertThrows(
            HttpClientResponseException::class.java
        ) { gatewayClient!!.createUser(user) }
        assertEquals(exception.status, HttpStatus.BAD_REQUEST)
        assertTrue(exception.response.getBody(String::class.java).orElse("").contains("Test error message"))
    }
}

1	Annotate the class with `@MicronautTest` so the Micronaut framework will initialize the application context and the embedded server. More info.

Edit application.yml

api/src/main/resources/application.yml

micronaut:
  application:
    name: api
authentication-credentials:
  username: ${username} (1)
  password: ${password} (2)

1	Placeholder for username that will be populated by Kubernetes.
2	Placeholder for password that will be populated by Kubernetes.

Edit the bootstrap.yml file in the resources directory to enable distributed configuration so it looks like the following:

api/src/main/resources/bootstrap.yml

micronaut:
  application:
    name: api
  config-client:
    enabled: true (1)
kubernetes:
  client:
    secrets:
      enabled: true (2)
      use-api: true (3)

1	Set `microanut.config-client.enabled: true` to read and resolve configuration from distributed sources.
2	Set `kubernetes.client.secrets.enabled: true` to enable Kubernetes secrets as a distributed source.
3	Set `kubernetes.client.secrets.use-api: true` to use the Kubernetes API to fetch configuration.

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

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

authentication-credentials:
  username: "test_username" (1)
  password: "test_password" (2)

1	Hardcoded username for development environment.
2	Hardcoded password for development environment.

Create a file named bootstrap-dev.yml to disable distributed configuration in the dev environment:

api/src/main/resources/bootstrap-dev.yml

micronaut:
  http:
    services:
      users:
        urls:
          - http://localhost:8081 (1)
      orders:
        urls:
          - http://localhost:8082 (2)
kubernetes:
  client:
    secrets:
      enabled: false (3)

1	URL of the `users` microservice
2	URL of the `orders` microservice
3	Disable Kubernetes secrets client.

Create a file named application-test.yml to be used in the test environment:

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

authentication-credentials:
  username: "test_username" (1)
  password: "test_password" (2)

1	Hardcoded username for development environment.
2	Hardcoded password for development environment.

Run the unit test:

api

./mvnw test

4.3.2. Running the application

Run api microservice:

api

MICRONAUT_ENVIRONMENTS=dev ./mvnw mn:run

14:28:34.034 [main] INFO  io.micronaut.runtime.Micronaut - Startup completed in 499ms. Server Running: http://localhost:8080

4.4. Test integration between applications

Store the URL of the api microservice in the API_URL environment variable.

export API_URL=http://localhost:8080

Run a cURL command to create a new user via the api microservice:

curl -X "POST" "$API_URL/api/users" -H 'Content-Type: application/json; charset=utf-8' -d '{ "first_name": "Nemanja", "last_name": "Mikic", "username": "nmikic" }'

{"id":1,"username":"nmikic","first_name":"Nemanja","last_name":"Mikic"}

Run a cURL command to a new order via the api microservice:

curl -X "POST" "$API_URL/api/orders" -H 'Content-Type: application/json; charset=utf-8' -d '{ "user_id": 1, "item_ids": [1,2] }'

{"id":1,"user":{"first_name":"Nemanja","last_name":"Mikic","id":1,"username":"nmikic"},"items":[{"id":1,"name":"Banana","price":1.5},{"id":2,"name":"Kiwi","price":2.5}],"total":4.0}

Run a cURL command to list created orders:

curl "$API_URL/api/orders" -H 'Content-Type: application/json; charset=utf-8'

[{"id":1,"user":{"first_name":"Nemanja","last_name":"Mikic","id":1,"username":"nmikic"},"items":[{"id":1,"name":"Banana","price":1.5},{"id":2,"name":"Kiwi","price":2.5}],"total":4.0}]

We can try to place an order for a user who doesn’t exist (with id 100). Run a cURL command:

curl -X "POST" "$API_URL/api/orders" -H 'Content-Type: application/json; charset=utf-8' -d '{ "user_id": 100, "item_ids": [1,2] }'

{"message":"Bad Request","_links":{"self":[{"href":"/api/orders","templated":false}]},"_embedded":{"errors":[{"message":"User with id 100 doesn't exist"}]}}

5. Kubernetes and the Micronaut framework

In this chapter we will first create the necessary Kubernetes resources for our microservices that will make them work properly then we will configure build container images and deploy each of the microservices that we created on the local Kubernetes cluster.

Create a filed named auth.yml that will service role for microservices that have secret configurations.

auth.yml

apiVersion: v1
kind: Namespace (1)
metadata:
  name: micronaut-k8s
---
apiVersion: v1
kind: ServiceAccount (2)
metadata:
  namespace: micronaut-k8s
  name: micronaut-service
---
kind: Role (3)
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  namespace: micronaut-k8s
  name: micronaut_service_role
rules:
  - apiGroups: [""]
    resources: ["services", "endpoints", "configmaps", "secrets", "pods"]
    verbs: ["get", "watch", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding (4)
metadata:
  namespace: micronaut-k8s
  name: micronaut_service_role_bind
subjects:
  - kind: ServiceAccount
    name: micronaut-service
roleRef:
  kind: Role
  name: micronaut_service_role
  apiGroup: rbac.authorization.k8s.io
---
apiVersion: v1
kind: Secret (5)
metadata:
  namespace: micronaut-k8s
  name: mysecret
type: Opaque
data:
  username: YWRtaW4= (6)
  password: bWljcm9uYXV0aXNhd2Vzb21l (7)

1	We create a namespace named `micronaut-k8s`.
2	We create a service account named `micronaut-service`.
3	We create a role named `micronaut_service_role`.
4	We bind the `micronaut_service_role` role to the `micronaut-service` service account.
5	We create a secret named `mysecret`.
6	Base64 value of the username secret that will be used by the microservices.
7	Base64 value of the password secret that will be used by the microservices.

Run the next command to create the resources described above:

kubectl apply -f auth.yml

Before we start deploying each service, ensure that Docker daemon is configured to use Kubernetes. If you are using Minikube run the next command to switch the docker daemon to use Minikube.

eval $(minikube docker-env)

5.1. Users Microservice

Build a docker image of the users service with the name users.

Edit the file named k8s.yml inside the users microservice.

/users/k8s.yml

apiVersion: apps/v1
kind: Deployment
metadata:
  namespace: micronaut-k8s
  name: "users"
spec:
  selector:
    matchLabels:
      app: "users"
  template:
    metadata:
      labels:
        app: "users"
    spec:
      serviceAccountName: micronaut-service (1)
      containers:
        - name: "users"
          image: users (2)
          imagePullPolicy: Never (3)
          ports:
            - name: http
              containerPort: 8080
          readinessProbe:
            httpGet:
              path: /health/readiness
              port: 8080
            initialDelaySeconds: 5
            timeoutSeconds: 3
          livenessProbe:
            httpGet:
              path: /health/liveness
              port: 8080
            initialDelaySeconds: 5
            timeoutSeconds: 3
            failureThreshold: 10
---
apiVersion: v1
kind: Service
metadata:
  namespace: micronaut-k8s
  name: "users" (4)
spec:
  selector:
    app: "users"
  type: NodePort
  ports:
    - protocol: "TCP"
      port: 8080  (5)

1	The service name that we created in the auth.yaml file.
2	The name of the container image for deployment.
3	The imagePullPolicy is set to Never. We will always use local one that we built in previous step.
4	Name of a service, required for service discovery.
5	Micronaut default port on which application is running.

Run the next command to create the resources described above:

kubectl apply -f users/k8s.yml

deployment.apps/users created
service/users created

5.2. Orders Microservice

Build a docker image of the orders service with the name orders.

Edit the file named k8s.yml inside the orders microservice.

/orders/k8s.yml

apiVersion: apps/v1
kind: Deployment
metadata:
  namespace: micronaut-k8s
  name: "orders"
spec:
  selector:
    matchLabels:
      app: "orders"
  template:
    metadata:
      labels:
        app: "orders"
    spec:
      serviceAccountName: micronaut-service  (1)
      containers:
        - name: "orders"
          image: orders  (2)
          imagePullPolicy: Never  (3)
          ports:
            - name: http
              containerPort: 8080
          readinessProbe:
            httpGet:
              path: /health/readiness
              port: 8080
            initialDelaySeconds: 5
            timeoutSeconds: 3
          livenessProbe:
            httpGet:
              path: /health/liveness
              port: 8080
            initialDelaySeconds: 5
            timeoutSeconds: 3
            failureThreshold: 10
---
apiVersion: v1
kind: Service
metadata:
  namespace: micronaut-k8s
  name: "orders"  (4)
spec:
  selector:
    app: "orders"
  type: NodePort
  ports:
    - protocol: "TCP"
      port: 8080  (5)

1	The service name that we created in the auth.yaml file.
2	The name of the container image for deployment.
3	The imagePullPolicy is set to Never. We will always use local one that we built in previous step.
4	Name of a service, required for service discovery.
5	Micronaut default port on which application is running.

Run the next command to create the resources described above:

kubectl apply -f orders/k8s.yml

5.3. API (Gateway) Microservice

Build a docker image of the api service with the name api.

Edit the file named k8s.yml inside the api microservice.

/api/k8s.yml

apiVersion: apps/v1
kind: Deployment
metadata:
  namespace: micronaut-k8s
  name: "api"
spec:
  selector:
    matchLabels:
      app: "api"
  template:
    metadata:
      labels:
        app: "api"
    spec:
      serviceAccountName: micronaut-service (1)
      containers:
        - name: "api"
          image: api  (2)
          imagePullPolicy: Never  (3)
          ports:
            - name: http
              containerPort: 8080
          readinessProbe:
            httpGet:
              path: /health/readiness
              port: 8080
            initialDelaySeconds: 5
            timeoutSeconds: 3
          livenessProbe:
            httpGet:
              path: /health/liveness
              port: 8080
            initialDelaySeconds: 5
            timeoutSeconds: 3
            failureThreshold: 10
---
apiVersion: v1
kind: Service
metadata:
  namespace: micronaut-k8s
  name: "api"  (4)
spec:
  selector:
    app: "api"
  type: LoadBalancer
  ports:
    - protocol: "TCP"
      port: 8080  (5)

1	The service name that we created in the auth.yaml file.
2	The name of the container image for deployment.
3	The imagePullPolicy is set to Never. We will always use local one that we built in previous step.
4	Name of a service, required for service discovery.
5	Micronaut default port on which application is running.

Run the next command to create the resources described above:

kubectl apply -f api/k8s.yml

5.4. Test integration between applications deployed on Kubernetes

Run the next command to check status of the pods and make sure that all of them have the status "Running":

kubectl get pods -n=micronaut-k8s

NAME                      READY   STATUS    RESTARTS   AGE
api-774fd667b9-dmws4      1/1     Running   0          24s
orders-74ff4fcbc4-dnfbw   1/1     Running   0          19s
users-9f46dd7c6-vs8z7     1/1     Running   0          13s

Run the next command to check the status of the microservices:

kubectl get services -n=micronaut-k8s

5.4.1. Minikube

For Minikube the output should be similar to the following:

NAME     TYPE           CLUSTER-IP       EXTERNAL-IP   PORT(S)          AGE
api      LoadBalancer   10.110.42.201    <pending>     8080:32601/TCP   18s
orders   NodePort       10.105.43.19     <none>        8080:31033/TCP   21s
users    NodePort       10.104.130.114   <none>        8080:31482/TCP   26s

By default, the EXTERNAL-IP address of the LoadBalancer service inside Minikube will be in the <pending> state. If you want to assign an external ip you have to run the minikube tunnel command.

Run the next command to retrieve the URL of the api microservice:

export API_URL=$(minikube service api -n=micronaut-k8s --url)

5.4.2. Docker Desktop

For Docker Desktop’s Kubernetes integration the output should be similar to the following. Notice the external-ip is localhost:

NAME     TYPE           CLUSTER-IP       EXTERNAL-IP   PORT(S)          AGE
api      LoadBalancer   10.108.205.248   localhost     8080:31516/TCP   9m23s
orders   NodePort       10.98.120.224    <none>        8080:31566/TCP   9m39s
users    NodePort       10.109.155.86    <none>        8080:30545/TCP   10m

So for Docker Desktop the API_URL should be set to http://localhost:8080.

Run a cURL command to create a new user via the api microservice:

curl -X "POST" "$API_URL/api/users" -H 'Content-Type: application/json; charset=utf-8' -d '{ "first_name": "Nemanja", "last_name": "Mikic", "username": "nmikic" }'

{"id":1,"username":"nmikic","first_name":"Nemanja","last_name":"Mikic"}

Run a cURL command to a new order via the api microservice:

curl -X "POST" "$API_URL/api/orders" -H 'Content-Type: application/json; charset=utf-8' -d '{ "user_id": 1, "item_ids": [1,2] }'

{"id":1,"user":{"first_name":"Nemanja","last_name":"Mikic","id":1,"username":"nmikic"},"items":[{"id":1,"name":"Banana","price":1.5},{"id":2,"name":"Kiwi","price":2.5}],"total":4.0}

Run a cURL command to list created orders:

curl "$API_URL/api/orders" -H 'Content-Type: application/json; charset=utf-8'

[{"id":1,"user":{"first_name":"Nemanja","last_name":"Mikic","id":1,"username":"nmikic"},"items":[{"id":1,"name":"Banana","price":1.5},{"id":2,"name":"Kiwi","price":2.5}],"total":4.0}]

We can try to place an order for a user who doesn’t exist (with id 100). Run a cURL command:

curl -X "POST" "$API_URL/api/orders" -H 'Content-Type: application/json; charset=utf-8' -d '{ "user_id": 100, "item_ids": [1,2] }'

{"message":"Bad Request","_links":{"self":[{"href":"/api/orders","templated":false}]},"_embedded":{"errors":[{"message":"User with id 100 doesn't exist"}]}}

6. Cleaning Up

To delete all resources that were created in this guide run next command.

kubectl delete namespaces micronaut-k8s

7. Next Steps

8. 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

Kubernetes service discovery and distributed configuration

1. Getting Started

2. What you will need

3. Solution

4. Writing the Apps

4.1. Users Microservice

4.1.1. Write tests to verify application logic

4.1.2. Running the application

4.2. Orders Microservice

4.2.1. Write tests to verify application logic

4.2.2. Running the application

4.3. API (Gateway) Microservice

4.3.1. Write tests to verify application logic

4.3.2. Running the application

4.4. Test integration between applications

5. Kubernetes and the Micronaut framework

5.1. Users Microservice

5.2. Orders Microservice

5.3. API (Gateway) Microservice

5.4. Test integration between applications deployed on Kubernetes

5.4.1. Minikube

5.4.2. Docker Desktop

6. Cleaning Up

7. Next Steps

8. License