Heroku

Step 1: Configure a port

First, specify a port to listen for incoming requests. Since Heroku uses the PORT environment variable, you need to configure your application to use the value of this variable. Depending on the way used to configure a Ktor server, do one of the following:

• If server configuration is specified in code, you can retrieve the environment variable value using System.getenv. Open the Application.kt file placed in the src/main/kotlin/com/example folder and change the port parameter value of the embeddedServer() function:

  fun main() { embeddedServer(Netty, port = System.getenv("PORT")?.toIntOrNull() ?: 8080) { // ... }.start(wait = true) }

• If your server configuration is specified in an application.conf file, you can assign the environment variable to the port parameter by using the ${ENV} syntax. Open the application.conf file placed in src/main/resources and update it as shown below:

  ktor { deployment { port = 8080 port = ${?PORT} } }

Step 2: Add a stage task

Open the build.gradle.kts file and add a custom stage task. Heroku uses the stage task to make an executable file that runs on Heroku's platform:

Step 3: Create a Procfile

Create a Procfile in a project root and add the following content to it:

This file specifies a path to the application's executable generated by the stage task and allows Heroku to start the application. You might need to replace ktor-get-started-sample with your project name.

Step 4: Specify the Java version (optional)

By default, Heroku uses Java 25 to run your application. If your Ktor application is compiled with a different Java version, you need to specify it explicitly to avoid deployment failures.

To specify the Java version, create a system.properties file in your project's root folder with the following content:

Replace 21 with your desired Java version.