Rider-to-driver matching
Design the rider-to-driver matching service for a ride-hailing platform operating in 200 cities, peaking at 30k ride requests/second globally with ~3M drivers broadcasting GPS updates every 4 seconds. A request must return up to 10 candidate drivers within ~2km in under 150ms p99, and a driver must never be offered to two riders at once. Walk through the geo-index, the dispatch loop, and how you keep consistency under concurrent matches.
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.