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System designMedium
Question
Design a simple group chat for a small team of about 50 people in a handful of channels. Messages should appear to other online members within a second or two, and a user who reconnects should be able to load the recent history of a channel. Volume is low — a few thousand messages a day. Cover how messages are stored, how real-time delivery works, and how history is fetched.
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
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