System designMediumsd-g243

Subject Upload pipelineLevel Mid–Senior~40 minCommon in Distributed systems interviewsIndustries Technology, Software development

Question

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.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.