CI/CD for Kotlin Projects with GitHub Actions: A Step-by-Step Guide

Introduction: Why CI/CD is Indispensable for Kotlin Development

Modern Kotlin development is not just about writing concise and safe code, but also about ensuring its continuous delivery. Whether you are creating a server-side application on Ktor, an Android app, or a multiplatform project, manual builds and testing quickly become a bottleneck. CI/CD (Continuous Integration / Continuous Deployment) automates these processes, reducing the risk of human error and accelerating the release of new features.

GitHub Actions is one of the most popular tools for implementing CI/CD, especially if your code is already hosted on GitHub. It integrates tightly with the Kotlin ecosystem, supports Gradle and Maven, and allows you to flexibly configure pipelines for any need. In this article, we will break down how to set up a complete cycle of building, testing, and deploying a Kotlin project using GitHub Actions.

GitHub Actions Basics: Workflow Structure

Before writing code, let's understand the basic concepts. A workflow in GitHub Actions is an automated process that is triggered by a specific event (e.g., a push to the main branch). A workflow is described in a YAML file stored in the .github/workflows/ directory of your repository.

A typical workflow structure includes:

• name — the name of the workflow (displayed in the GitHub interface).
• on — the trigger events (e.g., push, pull_request).
• jobs — a set of tasks that run sequentially or in parallel.
• steps — the steps within a job (setting up JDK, caching dependencies, running tests).

For Kotlin projects, a key step is configuring the correct JDK version (usually 11, 17, or 21) and using the Gradle Wrapper (./gradlew), which ensures build reproducibility on any machine.

Step 1: Basic Build and Test for a Kotlin Project

Let's start with the simplest thing: a workflow that runs tests on every push to main or when a Pull Request is created. This is the foundation of any CI/CD — ensuring that new code doesn't break existing functionality.

Create a file .github/workflows/ci.yml with the following content:

name: CI for Kotlin

on:  push:    branches: [ main ]  pull_request:    branches: [ main ]

jobs:  build:    runs-on: ubuntu-latest

    steps:      - uses: actions/checkout@v4

      - name: Set up JDK 17        uses: actions/setup-java@v4        with:          java-version: '17'          distribution: 'temurin'

      - name: Grant execute permission for gradlew        run: chmod +x gradlew

      - name: Cache Gradle packages        uses: actions/cache@v4        with:          path: |            ~/.gradle/caches            ~/.gradle/wrapper          key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}          restore-keys: |            ${{ runner.os }}-gradle-

      - name: Build with Gradle        run: ./gradlew build

      - name: Run tests        run: ./gradlew test

Let's break down the key points:

• actions/checkout@v4 — clones the repository into the runner.
• actions/setup-java@v4 — installs JDK 17 (Temurin). You can choose a different version if your project requires, for example, JDK 11 or 21.
• actions/cache@v4 — caches Gradle dependencies. This is critically important for speed: without a cache, each build would download all libraries from scratch (which can take 2-5 minutes). Caching speeds this up to a few seconds.
• ./gradlew build — a full project build (compilation + tests). If you only want tests, use ./gradlew test.