Feature flag store
Design a feature-flag toggle store for a single web application. Engineers want to turn features on/off (and roll out to a percentage of users) without redeploying. Flags are read on almost every request to decide which code path to take; they're changed only occasionally by humans through an admin page. Describe the storage and how the app reads flags fast.
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.