Java remains one of the most popular programming languages in the world and much of that use is happening in server-side backend systems. Kotlin can integrate smoothly with any of these JVM supported systems and can be integrated all at once, or bit by bit as developers become more familiar with the language. Kotlin can be used to deploy these applications to any system that supports Java web applications.
Kotlin tooling for server-side work is great as well. IntelliJ IDEA has full support for the language and there are additional plugins for popular frameworks such as Spring. JetBrains has also developed Ktor, an unopinionated framework for developing web applications with Kotlin. These tools aim to make it as easy as possible to use Kotlin for your server-side work.