#network

We analyze the reasons why hard cuts lead to failures in L4 Load Balancer and Nginx-WebSocket architecture from the connection lifecycle perspective.

We dissect what connection state changes actually occur in L4 Load Balancer by bind, unbind, and connection draining based on the TCP lifecycle.

We decompose Connection Draining into TCP lifecycle and explain how SYN, FIN, RST, TIME_WAIT, and CLOSE_WAIT appear in actual operational indicators.

The phenomenon of connection draining not ending due to WebSocket persistent connection is analyzed from the perspective of TCP, Nginx proxy, and application, and five solutions are presented.

The Zero Downtime Deployment procedure that can actually be operated in the L4 -> Nginx -> App -> WebSocket architecture is presented in a 7-step runbook.

Actual failure patterns caused by server removal without drain, WebSocket drain failure, and keepalive setting imbalance are analyzed through symptoms, logs, causes, and solutions.

We present a practical checklist to verify Connection Draining and Graceful Shutdown readiness within 10 minutes immediately before deployment in the L4/Nginx/App/WebSocket structure.