Nginx - Only handles exactly 500 request per second - How to increase the limit?

[agriz]

worker_processes auto; 
pid /run/nginx.pid; 
worker_rlimit_nofile 100000; 
error_log /var/log/nginx/error.log crit; 
events { 
worker_connections 4000; 
multi_accept on; 
use epoll; 
} 

http { 
include /etc/nginx/mime.types; 
sendfile on; 
tcp_nopush on; 
tcp_nodelay on; 
directio 4m; 
types_hash_max_size 2048; 

client_body_buffer_size 15K; 
client_max_body_size 8m; 

keepalive_timeout 20; 
client_body_timeout 15; 
client_header_timeout 15; 
send_timeout 10; 

open_file_cache max=5000 inactive=20s; 
open_file_cache_valid 60s; 
open_file_cache_min_uses 5; 
open_file_cache_errors off; 

gzip on; 
gzip_comp_level 2; 
gzip_min_length 1000; 
gzip_proxied any; 
gzip_types text/plain text/css application/json application/xjavascript
text/xml application/xml application/xml+rss text/javascript; 

access_log off; 
log_not_found off; 
include /etc/nginx/conf.d/*.conf; 
} 

The server has 8 cores and 32 gb ram. 
The load is 0.05 
But nginx is not able to handle more than 500 requests per second. 
The server suddenly received 1500 hits and goes down immediately. I have to
restart nginx.
Please tell me how to increase the limit

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,278237,278237#msg-278237