Which setting is limiting my active connections (ip_conntrack)?

I have a webserver with ispconfig (mysql & php & nginx). My munin statistic shows that there are the connecitons limited to about 9k. But I can't find a settings which is about 9000 which I could increase.

My system: Debian 9.8 / 128GB E5-1650v3 / nginx/1.10.3

My nginx settings are:

events {
    worker_connections 768;
    # multi_accept on;
}

Below are the the graphs which show the limit, all other graphs look normal.

Can you give me a hint which settings are responsible for the limited connections?

Solution 1:

Intel E5-1650v3 has 12 threads if hyperthreading is active. How many workers does your nginx use? If set to auto ("worker_processes auto;") it defaults to number of processors (12) and could limit your connections (12*768=9216). Increase worker_processes or worker_connections.

Have you checked your max open file (nofile) limits in /etc/security/limits.conf for the user running your nginx process?