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mediumSystem Design

How would you design a notification or chat system (fan-out, presence)?

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01

Understand the problem

Design real-time chat/notifications with WebSockets, presence, fan-out, and offline push.

notificationchatfanoutpresencewebsocketpubsub
02

Attempt it yourself

Sketch your approach before reading the solution — that's what interviews test.

Nudge consolestandby

Stuck? Beam a request up — the console returns a conceptual nudge that guides your logic without spoiling the implementation.

03

Study the solution

Step 1: Use Cases, Constraints, Assumptions, Back-of-Envelope

Use cases

We'll scope to handle only the core flows that expose the bottlenecks; everything else is deferred.

  • User sends message/notification — POST to API, persisted, fanned out to online recipients via WebSocket, offline via push (APNs/FCM).

Solution ready — 2 min read

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04

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Dossier 25 of 99 decoded in the System Design track. One more won't hurt.

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