Microservices are a type of software architecture that structures an application as a collection of loosely coupled services. This approach is taken in order to improve modularity, and to make development, deployment, and maintenance easier.
Kotlin is a statically typed programming language that runs on the Java Virtual Machine and can be used to develop Android apps, web apps, server-side applications, and more. Kotlin is fully compatible with the Java programming language, and is gaining popularity due to its concise syntax and null-safety features.
In this article, we'll take a look at how to build and deploy Kotlin microservices. We'll start by looking at what microservices are and why they're beneficial. We'll then look at how to create a Kotlin project using the Gradle build tool. Finally, we'll deploy our Kotlin microservice to a server.
Microservices are a type of software architecture that structures an application as a collection of loosely coupled services. This approach is taken in order to improve modularity, and to make development, deployment, and maintenance easier.
Microservices are typically built around business capabilities, and each microservice has a well-defined boundary. This boundary can be physical (e.g. different machines) or logical (e.g. different process).
Each microservice is responsible for a single business capability, and can be deployed and scaled independently of other microservices. This means that if one microservice needs to be updated, only that microservice needs to be redeployed - the other microservices can continue to run without interruption.
There are many benefits to using microservices, including:
Improved modularity: Microservices are typically built around business capabilities, which improves modularity and makes it easier to understand the application as a whole.
Easier development: Services can be developed and deployed independently, which means that developers can work on their own services without affecting other services.
Easier testing: Services can be tested independently, which makes it easier to identify and fix bugs.
Easier deployment: Services can be deployed independently, which means that updates can be made without affecting the rest of the application.
Easier scaling: Services can be scaled independently, which means that only the services that are being used need to be scaled.
In this section, we'll look at how to build a Kotlin microservice using the Gradle build tool. We'll start by creating a new Kotlin project using the Gradle Kotlin DSL.
First, we'll create a new Kotlin project using the Gradle Kotlin DSL. We'll name our project "helloworld-microservice":
$ gradle init --type kotlin-library
This will create a new Kotlin project with the following directory structure:
.
└── helloworld-microservice
├── build.gradle.kts
└── src
└── main
└── kotlin
└── com
└── example
└── helloworldmicroservice
└── HelloWorld.kt
Next, we'll add the following dependencies to our build.gradle.kts
file:
plugins {
kotlin("plugin.spring") version "1.3.72"
}
repositories {
mavenCentral()
}
dependencies {
implementation("org.springframework.boot:spring-boot-starter-web:2.3.3.RELEASE")
implementation("org.jetbrains.kotlin:kotlin-reflect:1.3.72")
implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.3.72")
testImplementation("org.springframework.boot:spring-boot-starter-test:2.3.3.RELEASE") {
exclude(group = "org.junit.vintage", module = "junit-vintage-engine")
}
}
The kotlin-spring
plugin adds support for the Spring Framework to Kotlin. The spring-boot-starter-web
dependency adds support for building web applications using Spring MVC. The kotlin-reflect
and kotlin-stdlib-jdk8
dependencies add support for reflection and the Java 8 Standard Library to Kotlin. The spring-boot-starter-test
dependency adds support for testing Spring applications.
Next, we'll create a Kotlin class that represents our microservice. We'll name our class HelloWorldService
and annotate it with the @Service
annotation:
@Service
class HelloWorldService {
fun sayHello(): String {
return "Hello, world!"
}
}
The @Service
annotation is used to mark a class as a Spring Bean. Spring Beans are managed by the Spring Framework, and can be injected into other Spring Beans.
Next, we'll create a Kotlin class that represents our microservice's HTTP API. We'll name our class HelloWorldController
and annotate it with the @RestController
annotation:
@RestController
class HelloWorldController(
private val helloWorldService: HelloWorldService
) {
@GetMapping("/hello")
fun sayHello(): String {
return helloWorldService.sayHello()
}
}
The @RestController
annotation is used to mark a class as a Spring MVC controller. Spring MVC controllers are responsible for handling HTTP requests and returning responses.
The HelloWorldController
class has a single sayHello()
method, which is annotated with the @GetMapping
annotation. This annotation maps the sayHello()
method to the /hello
HTTP endpoint.
Finally, we'll create a Kotlin class that represents our microservice's entry point. We'll name our class HelloWorldApplication
and annotate it with the @SpringBootApplication
annotation:
@SpringBootApplication
class HelloWorldApplication
fun main(args: Array<String>) {
runApplication<HelloWorldApplication>(*args)
}
The @SpringBootApplication
annotation is used to mark a class as a Spring Boot application. Spring Boot applications can be run using the java -jar
command.
In this section, we'll look at how to deploy a Kotlin microservice to a server. We'll start by looking at the different types of servers that can be used to deploy Kotlin microservices. We'll then look at how to deploy a Kotlin microservice to a Heroku dyno.
There are many different types of servers that can be used to deploy Kotlin microservices. The most common type of server is a dedicated server, which is a physical server that is owned and operated by a company. Dedicated servers can be expensive, and are typically used by large organizations.
Another type of server is a virtual private server (VPS), which is a server that is hosted on a shared physical server. VPSes can be cheaper than dedicated servers, and are typically used by small to medium-sized organizations.
Finally, there are cloud-based servers, which are servers that are hosted on a cloud computing platform. Cloud-based servers can be cheaper than both dedicated and VPS servers, and are typically used by small organizations.
Heroku is a cloud computing platform that offers a free tier for hobbyists and a paid tier for businesses. Heroku makes it easy to deploy, scale, and manage Kotlin microservices.
To deploy a Kotlin microservice to Heroku, we first need to create a new Heroku account and install the Heroku CLI. Once we have done this, we can create a new Heroku app and push our Kotlin microservice to it:
$ heroku create
$ git push heroku master
In this article, we've looked at how to build and deploy Kotlin microservices. We've seen how microservices can improve modularity, and how they can be deployed to different types of servers.