Live event chat at scale
Design the live-comment / live-chat system for a streamed event (sports final, product launch) with up to 5 million concurrent viewers in one room. Viewers post short comments; everyone sees a fast-moving feed. At peak there are 100k comments/min inbound but no human can read 5M/min, so the displayed stream must be sampled. Comments need light moderation (spam/abuse) before display, and the experience must feel live (<2 s). How do you ingest, moderate, and fan out at this scale?
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.