System designEasysd-g546

Subject Short poll presenceLevel Entry–Mid~25 minCommon in Distributed systems interviewsIndustries Software development, Technology

Question

Design a simple 'who's online' presence feature for a small collaboration app with a few hundred active users. The app should show which teammates are currently online, updating within a few seconds of someone going offline. You don't need history — just the current state. Cover how clients report presence, where the state lives, and how someone is detected as having gone offline.

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.