Blog comment system
Design a basic comment system for a blog. Each article can have comments, comments can have one level of replies (a reply to a top-level comment), and the article page shows comments newest-first with pagination. The site is read-heavy — many more views than new comments. Cover the data model, how you load comments for a page, and how you'd keep the read path fast.
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.