Deploying a Kotlin Application on VPS: A Step-by-Step Guide from A to Z

Deploying a Kotlin Application on VPS: Step by Step from A to Z

You've written a cool application in Kotlin (Ktor, Spring Boot, or just a console service), and now you need to run it on a real server. In this article, we will cover the full deployment cycle of a Kotlin application on a VPS: from purchasing a server and setting up SSH to launching via systemd and connecting a domain with HTTPS. All examples are working and tested on Ubuntu 22.04.

1. VPS Preparation and Connection

First, rent a VPS (for example, from Timeweb, Selectel, or DigitalOcean). Minimum requirements: 1 vCPU, 1 GB RAM, 20 GB SSD. Operating system — Ubuntu 22.04 LTS.

After receiving the IP address and root password, connect via SSH:

ssh root@your_server_ip

Immediately update the system and create an unprivileged user (working as root is bad practice):

apt update && apt upgrade -yadduser kotlinuserusermod -aG sudo kotlinusersu - kotlinuser

Set up SSH keys for convenient and secure login:

ssh-keygen -t ed25519 -C "your_email@example.com"ssh-copy-id kotlinuser@your_server_ip

Now disable password login in /etc/ssh/sshd_config (the line PasswordAuthentication no) and restart SSH: sudo systemctl restart sshd.

2. Installing Java (JRE/JDK) and Building the Application

Kotlin applications run on the JVM. Install OpenJDK 17 or 21 (recommended for modern projects):

sudo apt install openjdk-17-jdk -yjava -version

Now, on your local computer (where development is done), build the application into a JAR file. For Gradle (Ktor or Spring Boot):

./gradlew clean build

The finished JAR file will be in build/libs/. For example, myapp-1.0.0.jar. Upload it to the server:

scp build/libs/myapp-1.0.0.jar kotlinuser@your_server_ip:~/app/

Create the folder structure on the server:

mkdir -p ~/app/logs ~/app/config

Place configuration files (application.conf, application.yml) in ~/app/config/. Check that the application starts manually:

cd ~/appjava -jar myapp-1.0.0.jar --spring.config.location=file:./config/

If everything works, move on to automatic startup.

3. Setting up systemd for Autostart

To make the application automatically start after a server reboot and not crash on errors, we will create a systemd service.

Create the file /etc/systemd/system/kotlin-app.service:

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

Paste the following content (replace the paths with your own):

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

[Service]Type=simpleUser=kotlinuserWorkingDirectory=/home/kotlinuser/appExecStart=/usr/bin/java -jar /home/kotlinuser/app/myapp-1.0.0.jar --spring.config.location=file:/home/kotlinuser/app/config/Restart=on-failureRestartSec=10StandardOutput=append:/home/kotlinuser/app/logs/app.logStandardError=append:/home/kotlinuser/app/logs/error.log

[Install]WantedBy=multi-user.target

Explanation of key parameters:

• User — who to run it as (not root);
• ExecStart — the full launch command with the config specified;
• Restart=on-failure — automatic restart on crash;
• StandardOutput/Error — logging to files.

Activate the service:

sudo systemctl daemon-reloadsudo systemctl enable kotlin-app.servicesudo systemctl start kotlin-app.service

Check the status:

sudo systemctl status kotlin-app.service