Deploying Kotlin Application on VPS: Advanced Level

Deploying Kotlin Application on VPS: Step-by-Step Guide for Advanced Users

Developing in Kotlin is only half the battle. True mastery is demonstrated when your application starts running in a production environment on your own VPS server. In this article, we will cover advanced techniques for deploying Kotlin applications: from building a fat JAR to setting up uninterrupted operation with systemd, a reverse proxy via Nginx, and automation through CI/CD. The material is intended for developers who are already familiar with the basics of Kotlin and want to reach a professional level.

1. Preparing a Production Build of a Kotlin Application

The first step is creating an optimized build. We use the shadow plugin for Gradle, which packages all dependencies into a single executable JAR file (fat JAR).

Add to build.gradle.kts:

plugins {    kotlin("jvm") version "1.9.22"    id("com.github.johnrengelman.shadow") version "8.1.1"    application}

application {    mainClass.set("com.example.MainKt")}

tasks.shadowJar {    archiveBaseName.set("app")    archiveClassifier.set("")    archiveVersion.set("")    minimize()}

Build the JAR with the command:

./gradlew shadowJar

As a result, you will get the file build/libs/app.jar. For production, it is recommended to disable debug logs and configure the logging level via environment variables.

Example logback.xml configuration for production:

<configuration>    <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">        <file>/var/log/app/app.log</file>        <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">            <fileNamePattern>/var/log/app/app.%d{yyyy-MM-dd}.log</fileNamePattern>            <maxHistory>30</maxHistory>        </rollingPolicy>        <encoder>            <pattern>%d{yyyy-MM-dd HH:mm:ss} [%thread] %-5level %logger{36} - %msg%n</pattern>        </encoder>    </appender>

    <root level="INFO">        <appender-ref ref="FILE"/>    </root></configuration>

2. Creating a systemd Service for Automatic Startup

To ensure the application starts automatically on system boot and restarts on failure, we use systemd. Create the file /etc/systemd/system/kotlin-app.service:

[Unit]Description=Kotlin Application ServiceAfter=network.target

[Service]Type=simpleUser=appuserGroup=appuserWorkingDirectory=/opt/kotlin-appExecStart=/usr/bin/java -Xms512m -Xmx1024m -jar /opt/kotlin-app/app.jarRestart=on-failureRestartSec=10StandardOutput=journalStandardError=journalEnvironment="APP_ENV=production"Environment="DB_URL=jdbc:postgresql://localhost:5432/mydb"

[Install]WantedBy=multi-user.target

After creating the file, run:

sudo systemctl daemon-reloadsudo systemctl enable kotlin-appsudo systemctl start kotlin-app

Check the status:

sudo systemctl status kotlin-app

Logs can be viewed via journalctl -u kotlin-app -f.

3. Configuring Nginx as a Reverse Proxy with SSL

Nginx will provide load balancing, caching, and HTTPS. Install Nginx and Certbot:

sudo apt updatesudo apt install nginx certbot python3-certbot-nginx

Create the configuration /etc/nginx/sites-available/kotlin-app:

server {    listen 80;    server_name yourdomain.com;    return 301 https://$server_name$request_uri;}

server {    listen 443 ssl http2;    server_name yourdomain.com;

    ssl_certificate /etc/letsencrypt/live/yourdomain.com/fullchain.pem;    ssl_certificate_key /etc/letse