System designHardsd-g489

Subject Live streamingLevel Senior–Staff~50 minCommon in Distributed systems interviewsIndustries Computer games, Technology

Question

Design a WebRTC SFU (Selective Forwarding Unit) cluster for real-time multiplayer game spectating / co-watch where a host's gameplay video + audio is relayed to up to 100K live spectators per room with <500ms latency, and a subset (party of 8) are in a low-latency two-way voice/video chat over the same session. You can't mesh 100K peers and you can't transcode per-viewer at that fan-out, so you need an SFU topology that forwards selectively, scales horizontally across many SFU nodes, and degrades gracefully on bad networks.

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.