Idle timeout
Default 60s on most LBs. WebSockets need 300-3600s. Increase, then ping/pong under that interval.
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Sticky sessions
If your server holds per-connection state, sticky sessions help. Better: move state to a shared store so any backend handles any WebSocket.
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HTTP/2 upgrade issues
HTTP/2 doesn't officially support WebSocket (RFC 8441 does but adoption is spotty). Force HTTP/1.1 for WebSocket paths.