Resumable chunked upload
Design a resumable chunked upload service for a consumer file-sync product (think Dropbox) handling 50M daily uploads, files from 1KB to 50GB, over flaky mobile networks where a single TCP connection rarely survives a large transfer. Clients must be able to pause, resume after days, and switch networks without re-sending bytes. Read:write is roughly 4:1 and storage cost dominates the bill. Design the upload protocol, the chunk-tracking metadata, and how you deduplicate across users.
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.
Clarify4:30 left
Estimate4:30 planned
Design13:30 planned
Deep dive10:30 planned
Failure7:00 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.