Linux kernel parameter
net.core.somaxconn
somaxconn is used to set the maximum number of connections that can be queued for a socket. This parameter is used to prevent a flood of connection requests from overwhelming the system. The maximum value for the net.core.somaxconn parameter depends on the system and kernel version.
The default value for the net.core.somaxconn Linux kernel parameter is typically 128 and the maximum value is around 65535 on most systems.
For Nginx
It is important to set the net.core.somaxconn parameter to a value that is larger than the backlog value of NGINX, as the backlog value is used to determine the maximum number of connections that can be queued for a listening socket of NGINX only. If the net.core.somaxconn value is smaller than the backlog value, NGINX will not be able to queue all the incoming connections, resulting in connection errors.[1]