Syntax:     keepalive_requests number;
Default:     keepalive_requests 100;
Context:     upstream
This directive appeared in version 1.15.3.

Sets the maximum number of requests that can be served through one keepalive connection. After the maximum number of requests is made, the connection is closed.
Closing connections periodically is necessary to free per-connection memory allocations. Therefore, using too high maximum number of requests could result in excessive memory usage and not recommended.