How would you design a WhatsApp-scale message fanout system using WebSockets?
Updated May 6, 2026
Short answer
A fanout system distributes messages to millions of users using WebSockets, message queues, and partitioned storage.
Deep explanation
At WhatsApp scale, messages are not broadcast blindly. Instead, messages are stored first, then delivered via fanout-on-read or fanout-on-write strategies. WebSocket gateways handle live delivery, while Kafka/Redis ensures cross-node propagation. Offline users receive messages via persistent storage when they reconnect.
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