Yikes, looks… non-trivial.
If i use NSNotifications, will they post the notification prior to a server retirement similar to the KVO option?
The server may be long-gone in either case – the remote app doesn’t wait for the notification to be received, and sometimes you’ll receive a retirement notification when the SyphonServerDirectory notices a server has died long after the event. With NSNotifications (or a pre-change KVO) you will get a server description dictionary with details of the departed server though.