Video conferencing SFU
Design the media-routing backend for a group video-conferencing product (think 50-person calls, 5,000 concurrent meetings). Clients use WebRTC. You need <200 ms glass-to-glass latency, graceful degradation on bad networks, and the ability to scale a single large meeting beyond one server. Decide the topology (mesh vs. MCU vs. SFU), how you handle heterogeneous client bandwidth, and where the hard limits are.
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.