System designHardsd-g706

Subject Edge realtime sync protocolLevel Senior–Staff~50 minCommon in Networking & APIs · Distributed systems interviewsIndustries Technology, Software development

Question

Design the real-time sync backend for a collaborative offline-first app (think a shared notes/whiteboard tool) where 10M users edit documents that must converge across devices, work offline, and merge without a central lock. Edits stream over WebSocket when online and queue locally when offline. You need <500 ms propagation between online collaborators on a doc and automatic conflict resolution. How do edits flow, and how do you guarantee convergence?

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.