Hardening Server-Sent Events (SSE) and WebSockets in Node.js Under High Concurrent Connections

Kernel Sizing for 50,000+ Concurrent Persistent Sockets

Default Linux kernel configurations limit open file descriptors to 1,024, terminating inbound WebSocket connections under high volume. Proper tuning requires modifying OS limits and socket buffers.

Essential /etc/security/limits.conf Tuning

* soft nofile 65535
* hard nofile 65535

Implement periodic heartbeat ping/pong frames every 30 seconds to detect dead TCP connections caused by carrier network drops without wasting server resources.