System designMediumsd-g147

Subject GeofencingLevel Mid–Senior~40 minCommon in Distributed systems interviewsIndustries Technology

Question

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.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.