Use MonadUnliftIO on servant APIs.

unliftio-servant-server provides convenience functions for running servant APIs whose monads have a MonadUnliftIO instance.

UnliftIO Support for servant-server

Servant APIs written in any MonadUnliftIO m can be converted to wai Applications without writing the natural transformation by hand. These functions will return m Application which means that either:

1. You will have to serve from inside your MonadUnliftIO m monad, or
2. You will have to unwrap your application monad to IO, bind the Application, and then serve it in IO.

If you choose the second option, beware ResourceT --- trying to use the returned Application outside of a containing ResourceT risks attempting to interact with closed resources.