Proximity marketing geofence
Design a proximity-marketing geofence system that triggers an action (push notification, order-ahead prompt) when a user approaches one of 200k store locations, for an app with 30M installs. The catch: it must work with minimal battery drain on the device and tolerate phones being offline/backgrounded. Cover where geofence evaluation happens, how you select which fences a device watches, and avoiding spammy/duplicate triggers.
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.
Clarify4:30 left
Estimate4:30 planned
Design13:30 planned
Deep dive10:30 planned
Failure7:00 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.