CI/CD for Kotlin Projects: GitHub Actions from A to Z

Introduction to CI/CD for Kotlin with GitHub Actions

In modern development, automating the processes of building, testing, and deployment has become an integral part of a professional approach. For Kotlin projects, whether they are Android applications, backend services on Ktor, or multiplatform libraries, setting up CI/CD (Continuous Integration / Continuous Deployment) allows you to significantly reduce product time-to-market and lower the risk of errors.

GitHub Actions is a powerful and flexible tool built into the GitHub ecosystem. It allows you to create custom pipelines that automatically run on pushes, pull requests, or on a schedule. In this article, we will cover the complete cycle of setting up CI/CD for Kotlin: from basic code checks to automatic deployment.

GitHub Actions Basics: Structure and Syntax

Before diving into Kotlin specifics, it's important to understand the basic concepts of GitHub Actions. The pipeline is described in YAML files stored in the .github/workflows/ directory of your repository.

Key Workflow Elements

• Event: a trigger that starts the pipeline (push, pull_request, release, etc.).
• Job: a set of steps executed on one runner (virtual machine).
• Step: a specific action — executing a command, running a script, or using a pre-built action.
• Runner: the execution environment (Ubuntu, Windows, macOS).

Basic structure of the kotlin-ci.yml file:

name: Kotlin CI

on:  push:    branches: [ main, develop ]  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: Build with Gradle        run: ./gradlew build

Setting up CI for Kotlin: Build, Tests, and Linting

The first and most important stage is continuous integration. It ensures that every new piece of code compiles and does not break existing tests.

Caching Gradle Dependencies

To speed up the build, be sure to use caching. Without it, each run will download all libraries from scratch.

- name: Cache Gradle packages  uses: actions/cache@v3  with:    path: |      ~/.gradle/caches      ~/.gradle/wrapper    key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}    restore-keys: |      ${{ runner.os }}-gradle-

Running Tests and Style Checks

Let's add steps for running unit tests and a linter (detekt or ktlint). This helps maintain code quality.

- name: Run tests  run: ./gradlew test

- name: Run linter  run: ./gradlew detekt

Example of a Complete CI Workflow for a Kotlin Project

jobs:  test:    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: Cache Gradle        uses: actions/cache@v3        with:          path: ~/.gradle/caches          key: ${{ runner.os }}-gradle-${{ hashFiles('*.gradle.kts') }}      - name: Build and test        run: ./gradlew check

Continuous Deployment: Automatic Deployment of Kotlin Applications

After successful integration comes the deployment stage. For Kotlin projects, this could mean publishing a library to Maven Central, deploying a backend to a server, or building an APK for Android.

Deploying a Backend Service on Ktor

Let's say we have a Kotlin application using the Ktor framework. We want to automatically