Small team chat
Design a simple group chat for a small team of about 50 people in a handful of channels. Messages should appear to other online members within a second or two, and a user who reconnects should be able to load the recent history of a channel. Volume is low — a few thousand messages a day. Cover how messages are stored, how real-time delivery works, and how history is fetched.
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.
Clarify4:00 left
Estimate4:00 planned
Design11:30 planned
Deep dive9:30 planned
Failure6:00 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.