Sort of off topic: I had fun writing feature flag system for java/spring for work. We rolled a lot of our own stuff for tighter integration and this was not ex

Sort of off topic: I had fun writing feature flag system for java/spring for work. We rolled a lot of our own stuff for tighter integration and this was not exception. You could define an interface, slap on a special annotation and spring would provide an instance backed by a proxy. And this was for a web app, and so we made the toggles would configurable in the main app by admins. The UI for targeted roll outs was pretty simple but powerful. I never got around to adding mandatory cleanup dates, but it wouldn't be very hard. Adding automatic a/b tests would certainly have been a lot harder. We did find them very nice for fresh implementations of common workflow screens. It was a big app and invariably some functionality would be missed and so we could just turn of the migrated section until we fixed it. Definitely had to do more QA work, but it shortened the turn around time and reduced the stress quite a bit because patches weren't as urgent.