Why use Kotlin for server-side
Features of Kotlin:
Expressiveness: It uses features like type-safe builders and delegated properties which uses the concept of abstraction.
Scalability: It allows a developer to develop such applications which can support a large number of user with modest hardware requirements.
Interoperability: Kotlin can be used with java based frameworks.
Migration: A old system written in java can be converted into kotlin based system.
Tools: Good tools like IntelliJ Ide is available there for its programming.
Frameworks for server-side programming:
There are many server-side frameworks for kotlin for instance spring,ktor and etc.
Where to deploy your application:
There are many options are available there for example google cloud, Amazon, and Heroku.