System designHardsd-g526

Subject WebsocketsLevel Senior–Staff~50 minCommon in Security · Networking & APIs · Distributed systems interviewsIndustries Computer games, Technology, Software development

Question

Design the room/session backend for a real-time multiplayer collaborative or game app where state is room-scoped (a game match, a whiteboard, a watch-party). Each room has an authoritative live state mutated by member actions and broadcast to all members. Scale: 1M concurrent rooms, up to 1,000 members in the largest rooms, sub-150ms action-to-broadcast. Rooms are created/destroyed constantly; a room's host node can crash.

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.