Deploying a Kotlin Application on VPS: Step-by-Step Guide

Deploying a Kotlin Application on VPS: A Complete Step-by-Step Guide

Developing in Kotlin is only half the battle. Sooner or later, the question arises: how to move an application from a local environment to a real server? In this article, we will thoroughly examine deploying a Kotlin application (using Spring Boot as an example) on a VPS. You will learn how to prepare the server, build a JAR file, configure auto-start, and ensure a secure connection via HTTPS. This guide is suitable for both beginners and developers who want to systematize their knowledge.

1. Preparing the VPS and Installing Necessary Software

Before uploading the code, you need to prepare the server. We recommend using Ubuntu 22.04 LTS or newer. Connect to the server via SSH:

ssh root@your-server-ip

Update the package database and install Java (Kotlin compiles to JVM bytecode, so we need JDK 17 or 21):

sudo apt update && sudo apt upgrade -ysudo apt install openjdk-17-jdk -yjava -version

Make sure the Java version matches your build. Also install Git (if using a repository) and utilities for working with archives:

sudo apt install git unzip curl -y

To work with a Kotlin project on the server, it is not necessary to install the Kotlin compiler itself — we will perform the build locally or via CI/CD. However, if you plan to compile on the server, add SDKMAN! and Kotlin:

curl -s "https://get.sdkman.io" | bashsource "$HOME/.sdkman/bin/sdkman-init.sh"sdk install kotlin

Important: At this stage, also configure the firewall (UFW) for basic security:

sudo ufw allow OpenSSHsudo ufw allow 8080/tcp  # application portsudo ufw enable

2. Building the Kotlin Application and Transferring it to the Server

Consider a typical Spring Boot project with Kotlin. Build the JAR file locally (or on the server if you cloned the repository). In the project root, run:

./gradlew clean bootJar

Or, if using Maven:

mvn clean package

After the build, a file like app-0.0.1-SNAPSHOT.jar will appear in the build/libs/ (Gradle) or target/ (Maven) folder. Copy it to the server using SCP:

scp build/libs/app-0.0.1-SNAPSHOT.jar root@your-ip:/opt/myapp/app.jar

Create a directory for the application on the server and move the JAR:

sudo mkdir -p /opt/myappsudo mv app.jar /opt/myapp/

Check that the JAR starts manually:

cd /opt/myappjava -jar app.jar --server.port=8080

If the application starts and responds on port 8080, everything is fine. Stop it (Ctrl+C) and proceed to configure persistent startup.

3. Configuring systemd for Auto-Start and Monitoring

To make the application automatically start when the server reboots and recover after crashes, we will create a systemd service. Create a file:

sudo nano /etc/systemd/system/kotlin-app.service

Insert the following template (replace the parameters for your application):

[Unit]Description=Kotlin Spring Boot ApplicationAfter=network.target

[Service]Type=simpleUser=rootWorkingDirectory=/opt/myappExecStart=/usr/bin/java -jar /opt/myapp/app.jar --server.port=8080Restart=on-failureRestartSec=10StandardOutput=journalStandardError=journal

[Install]WantedBy=multi-user.target

Reload the systemd configuration and start the service:

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

If the status is active (running), everything is working. Add the service to auto-start:

sudo systemctl enable kotlin-app