How to find out who restricts access from IP?

Question

linux

The point is this. There is a bot (django -> gunicorn -> nginx -> debian 9 -> dedic 24 core 64gb ram). The server accepts about 100 requests per minute, after which the callback stops accepting. Suspicions that something from the chain above restricts requests from one IP. IPtables is not installed. there are no restrictions in nginx configs. What other software can restrict connections from one IP?

Answer 1

say iptables-save and see if there are rules potentially limiting your requests
exclude nginx - send requests directly to gunicorn, measure the result
monitor the number of connections
look at the logs for too many open files