Multi-region price invalidation
An e-commerce catalog service caches product price + availability in a multi-region cache (one cache cluster per region, 5 regions). A price change must propagate everywhere within ~10 seconds, and you must never serve a stale-cheaper price after the change is acknowledged. Writes happen in one primary region. Design the invalidation pipeline and explain how you handle out-of-order invalidation messages and a region whose invalidation bus is temporarily down.
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.
Clarify5:00 left
Estimate5:00 planned
Design15:00 planned
Deep dive12:00 planned
Failure8:00 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.