WebSocket gateway tier
Design the WebSocket gateway tier for a platform with 10M concurrent persistent connections. Requirements: route a message destined for user U to whichever gateway node holds U's socket; survive node restarts/deploys without dropping all connections at once; handle reconnect storms (a deploy or network blip reconnects millions at once); and keep per-connection memory low. Messages must not be lost across a brief reconnect.
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.