System designHardsd-g576

Subject System designLevel Mid–Senior~45 minCommon in Distributed systems interviewsIndustries Software development, Technology

Question

Design an activity feed for a mid-size social/collaboration app with ~2M users where users follow each other and a home feed shows recent activity from everyone you follow. Distribution is skewed: most users follow ~150 accounts, but some 'power' accounts have 100K+ followers. Requirements: home-feed loads in <150ms p95 (read-heavy), new activity appears within seconds, feeds are reverse-chronological with light ranking, and the system shouldn't fall over when a power account posts (the fan-out spike). Roughly 20:1 read:write on activity.

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.