Ktor 3.6.1 Help

Deploy a Ktor app to Google App Engine

In this tutorial, you will learn how to prepare and deploy a Ktor project to a Google App Engine standard environment. The tutorial uses the engine-main sample project as a starting point.

Prerequisites

Before starting this tutorial, complete the steps below:

  • Register on Google Cloud Platform.

  • Install and initialize the Google Cloud SDK.

  • Install the App Engine extension for Java with the following command:

    gcloud components install app-engine-java

Clone a sample application

To open a sample application, follow the steps below:

  1. Clone the Ktor documentation repository and open the codeSnippets project.

  2. Open the engine-main module.

Prepare an application

Step 1: Apply the Shadow plugin

This tutorial shows how to deploy your application to Google App Engine using a fat JAR. To generate fat JARs, you must apply the Shadow plugin.

First, open your gradle/libs.versions.toml file and define the Shadow plugin version and its alias:

[versions] shadow = "8.3.10" [plugins] shadow = { id = "com.gradleup.shadow", version.ref = "shadow" }

Then, open the build.gradle.kts file and add the plugin to the plugins block:

plugins { alias(libs.plugins.shadow) }

Step 2: Configure the App Engine plugin

The Google App Engine Gradle plugin provides tasks to build and deploy Google App Engine applications. To use this plugin, follow the steps below:

  1. Open the settings.gradle.kt file and use the following code to reference a plugin from the Central Maven repository:

    pluginManagement { repositories { if (!providers.gradleProperty("build_snapshot_train").orNull.isNullOrEmpty()) { mavenLocal() maven("https://redirector.kotlinlang.org/maven/dev") } gradlePluginPortal() mavenCentral() maven("https://redirector.kotlinlang.org/maven/ktor-eap") } resolutionStrategy { eachPlugin { if (requested.id.id.startsWith("com.google.cloud.tools.appengine")) { useModule("com.google.cloud.tools:appengine-gradle-plugin:${requested.version}")

  2. Open the build.gradle.kts file and apply the plugin in the plugins block:

    plugins { alias(libs.plugins.appengine) }

  3. In the same build.gradle.kts file, add the appengine block with the following settings:

    import com.google.cloud.tools.gradle.appengine.appyaml.AppEngineAppYamlExtension configure<AppEngineAppYamlExtension> { stage { setArtifact("build/libs/${project.name}-all.jar") } deploy { version = "GCLOUD_CONFIG" projectId = "GCLOUD_CONFIG" } }

Step 3: Configure App Engine settings

You configure App Engine settings for your application in the app.yaml file:

  1. Create the appengine directory inside src/main.

  2. Inside this directory, create the app.yaml file and add the following content:

    runtime: java21 entrypoint: 'java -jar google-appengine-standard-all.jar'

    Replace google-appengine-standard with your project's name.

    The entrypoint option contains a command used to run a fat JAR generated for the application.

Deploy an application

To deploy your application, open a new terminal window and follow the steps below:

  1. First, create a Google Cloud project, which is a top-level container holding application resources. For example, the command below creates a project with the ktor-sample-app-engine name:

    gcloud projects create ktor-sample-app-engine --set-as-default

  2. Create an App Engine application for the Cloud project:

    gcloud app create

  3. To deploy the application, run the appengineDeploy Gradle task:

    ./gradlew appengineDeploy

  4. Wait until Google Cloud builds and publishes the application:

    ...done. Deployed service [default] to [https://ktor-sample-app-engine.ew.r.appspot.com]

30 October 2026
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