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Socket.IO with Redis adapter: CORS across multiple Node servers, sticky sessions, and polling fallbacks
Engine.IO transports must share CORS settings on every node—sticky load balancing keeps sessions coherent with WebSocket upgrades.
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socket.iorediscors
Namespaces
Different namespaces may need different `origins` callbacks—avoid one global wildcard in regulated industries.
Admin namespaces should not be reachable from public SPAs without extra auth.
Redis cluster
Pub/sub channel saturation looks like disconnect storms—monitor separately from CORS errors.
Failover during Redis migration can drop messages—surface user-visible reconnect banners.