Team presence detection
Design a simple 'who's online' presence feature for a small collaboration app with a few hundred active users. The app should show which teammates are currently online, updating within a few seconds of someone going offline. You don't need history — just the current state. Cover how clients report presence, where the state lives, and how someone is detected as having gone offline.
What a strong answer looks like
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.
Clarify3:00 left
Estimate3:00 planned
Design8:30 planned
Deep dive6:30 planned
Failure4:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.