Design a Chat System — From DM to a Million Users
Chat system design at every scale: message store, conversation index, WebSocket fanout, presence, read receipts, and offline delivery.
Chat
Design WhatsApp / Chat — A System Design Walkthrough
End-to-end system design for a WhatsApp / Telegram-style chat. WebSocket fleet, message storage, delivery receipts, online presence, group chat fanout, end-to-end encryption, and the operational realities of running it at scale.