It's impossible to create any server apps in iOS.
iOS permits in background the following tasks only:
Play audio: the app can continue playing and/or recording audio in the background.
Receive location updates: the app can continue to get callbacks as the device’s location changes.
Perform finite-length tasks: the generic “whatever” case, where the app can run arbitrary code for a limited amount of time.
Background Fetch: Get updates to the latest content scheduled by iOS.