ETA prediction
Design the ETA / travel-time prediction service behind a maps and ride-hailing product: 1M ETA requests/second, each a (origin, destination) pair, p99 under 100ms, reflecting live traffic that updates continuously from probe data. Cover how you represent the road network, compute routes at scale, incorporate live traffic, and what you precompute vs compute on demand.
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.
Clarify5:30 left
Estimate5:30 planned
Design16:30 planned
Deep dive13:30 planned
Failure9:00 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.