Image thumbnail service
Design a simple image-thumbnail service for a small blog platform. Users upload an original photo (up to ~5 MB) and the site needs a 200x200 thumbnail to show in post lists. Traffic is modest: a few hundred uploads a day, reads dominated by visitors loading post pages. Walk through the components, where you store the images, and how thumbnails get generated.
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.
Clarify3:00 left
Estimate3:00 planned
Design8:30 planned
Deep dive6:30 planned
Failure4:00 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.