deploy.md

In this topic, we'll make an overview of how to deploy a Ktor application.

To simplify the deployment process of server Ktor applications, you can use the Ktor plugin for Gradle, which provides the following capabilities:

• Building fat JARs.
• Dockerizing your applications.

Ktor deployment specifics {id="ktor-specifics"}

The deployment process for a server Ktor application depends on the following specifics:

• Whether you are going to deploy your application as a self-contained package or inside a servlet container.
• Which approach do you use to create and configure a server.

Self-contained app vs Servlet container {id="self-contained-vs-servlet"}

Ktor allows you to create and start a server with the desired network engine (such as Netty, Jetty, or Tomcat) right in the application. In this case, an engine is a part of your application. Your application has control over engine settings, connection, and SSL options. To deploy your application, you can package it as a fat JAR or an executable JVM application.

In contrast to the approach above, a servlet container should control the application lifecycle and connection settings. Ktor provides a special ServletApplicationEngine engine that delegates control over your application to a servlet container. To deploy inside a servlet container, you need to generate a WAR archive.

Configuration: code vs configuration file {id="code-vs-config"}

Configuring a self-contained Ktor application for deployment might depend on the approach used to create and configure a server: in code or by using a configuration file. As an example, a hosting provider may require specifying a port used to listen for incoming requests. In this case, you need to configure a port either in code or in the application.conf/application.yaml.

Packaging {id="packaging"}

Before deploying your application, you need to package it in one of the following ways:

• Fat JAR

  A fat JAR is an executable JAR that includes all code dependencies. You can deploy it to any cloud service that supports fat JARs. A fat JAR is also required if you need to generate a native binary for GraalVM. To create a fat JAR, you can use the Ktor plugin for Gradle or the Assembly plugin for Maven.

• Executable JVM application

  An executable JVM application is a packaged application that includes code dependencies and generated start scripts. For Gradle, you can use the Application plugin to generate an application.

• WAR

  A WAR archive lets you deploy your application inside a servlet container, such as Tomcat or Jetty.

• GraalVM

  Ktor server applications can make use of GraalVM in order to have native images for different platforms.

Containerizing {id="containerizing"}

After you package your application (for example, to an executable JVM application or a fat JAR), you can prepare a Docker image with this application. This image can then be used to run your application on Kubernetes, Swarm, or a required cloud service container instance.

Publishing {id="publishing"}

Tutorials below show how to deploy a Ktor application to specific cloud providers:

SSL {id="ssl"}

If your Ktor server is placed behind a reverse proxy (such as Nginx or Apache) or runs inside a servlet container (Tomcat or Jetty), SSL settings are managed by a reverse proxy or a servlet container. If required, you can configure Ktor to serve SSL directly by using Java KeyStore.

Note that SSL settings are not in effect when a Ktor application is deployed inside a servlet container.