System designHardsd-g137

Subject GeofencingLevel Senior–Staff~45 minCommon in Distributed systems interviewsIndustries Technology

Question

Design a geofencing service that evaluates 2M device location updates per second against 10M active geofences (arbitrary polygons, some overlapping) and emits enter/exit/dwell events with under 1s latency. Geofences are created/deleted dynamically by tenants. Walk through the spatial index, the enter/exit state machine, and how you keep per-device fence membership consistent.

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.