Design a chat app
A system design walkthrough of a chat application like WhatsApp or Slack: requirements and estimates, WebSocket connections and gateways, message flow and delivery receipts, message storage and IDs, group chats and fan-out, presence, offline users and push notifications, ordering, and scaling.
CodexBash, , 6 min read
"Design a chat application" is a classic system design question because chat combines several hard problems in one familiar product: millions of long-lived connections, real-time delivery, reliable storage, ordering, group fan-out, presence and offline users. This article designs a WhatsApp-style messaging service step by step, covering the decisions an interviewer expects you to discuss and the trade-offs behind them.
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