Serverless Functions in Kotlin: AWS Lambda and Alternatives

Serverless in Kotlin: AWS Lambda and Analogues — Writing Serverless Code That Works

Once upon a time, writing a backend was synonymous with setting up servers, configuring Nginx, and sleepless nights monitoring load. Today, everything is different. Serverless is not science fiction, but a reality that allows you to forget about hardware and focus on application logic. And if you write in Kotlin, you get elegant, safe, and fast code that fits perfectly into a serverless architecture.

In this article, we will break down how to create serverless functions in Kotlin, which cloud providers offer the best conditions, and how not to get bogged down in configuration details. Let's go!

What is Serverless and Why Kotlin is the Ideal Choice

Serverless (or serverless computing) is a cloud computing model where you write code, and the provider handles the infrastructure. You don't pay for an idle server — only for the execution time of the function. Sounds like a dream? This is especially relevant for Kotlin.

Why Kotlin? Firstly, it compiles to JVM bytecode, providing native support on AWS Lambda, Google Cloud Functions, and Azure Functions. Secondly, Kotlin is a modern language with zero-cost abstractions, lambdas, and coroutines. Thirdly, its syntax allows you to write concise code that is easy to maintain.

Key advantages of serverless functions in Kotlin:

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• Cost Savings — pay only for actual code execution.
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• Scaling — the cloud decides how many instances to run.
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• Simplicity — no need to configure a server.
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• Quick Start — deploy with a single command.
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But there are nuances: a "cold start" can take up to several seconds, especially for JVM languages. However, modern providers have learned to deal with this: AWS Lambda with Provisioned Concurrency or Google Cloud Functions with min-instances solve the problem.

AWS Lambda: The King of Serverless Computing

Let's start with the most popular service — AWS Lambda. Amazon Web Services offers a mature ecosystem where Kotlin works "out of the box" via the Java Runtime.

How to Set Up AWS Lambda for Kotlin

You will need Gradle or Maven. We use Gradle with the Kotlin plugin. Example build.gradle.kts:

plugins {\n    kotlin("jvm") version "1.9.0"\n    id("com.github.johnrengelman.shadow") version "7.1.2"\n}\n\ndependencies {\n    implementation("com.amazonaws:aws-lambda-java-core:1.2.2")\n    implementation("com.amazonaws:aws-lambda-java-events:3.11.0")\n}\n\ntasks {\n    shadowJar {\n        archiveBaseName.set("lambda-function")\n        archiveClassifier.set("")\n    }\n}

Now let's write the function itself. AWS Lambda expects a class with a handleRequest method. Here is a simple handler that returns a greeting:

import com.amazonaws.services.lambda.runtime.Context\nimport com.amazonaws.services.lambda.runtime.RequestHandler\n\nclass HelloHandler : RequestHandler<Map<String, String>, String> {\n    override fun handleRequest(input: Map<String, String>, context: Context): String {\n        val name = input["name"] ?: "World"\n        return "Hello, $name! Your serverless function in Kotlin is working!"\n    }\n}

Build the fat JAR: ./gradlew shadowJar. Upload it to AWS Lambda, specify runtime Java 11 or Java 17. Done!

Working with AWS Events

Often, Lambda reacts to S3, DynamoDB, or API Gateway events. Example handler for S3:

import com.amazonaws.services.lambda.runtime.events.S3Event\n\nclass S3Handler : RequestHandler<S3Event, String> {\n    override fun handleRequest(event: S3Event, context: Context): String {\n        val bucket = event.records.f