Php-fpm always fails

Php-fpm always hangs on a newly created Project & nbsp; switch to an online domain name (a bit of traffic) & nbsp; 502 & nbsp. Log is & nbsp; similar to [error] & nbsp; 3169 #0: & nbsp; * 1 & nbsp; connect () & nbsp; failed & php-fpm always hangs
When a newly created Project is switched to an online domain name (with a relatively high access Volume), 502 of the total traffic is displayed.

Logs are similar

[Error] 3169 #0: * 1 connect () failed (111: Connection refused) while connecting to upstream, client: 127.0.0.1, server: localhost, request: "GET/index. php HTTP/1.1 ", upstream:" fastcgi: // 127.0.0.1: 9000 ", host:" 127.0.0.1"

It seems that fpm is not started at all ..

Debug the SQL statement before (output the SQL statement in the header, and 502 may occur if there is a large amount of data ). Now we have disabled some header output. When the traffic volume is large.
If you change the domain name, there will be no access issues. What is the cause of this situation. Thank you!

------ Solution --------------------
Set worker_rlimit_nofile of nginx to the same value as ulimit-n.

In addition, set the rlimit_files parameter of the php-fpm.conf to the same value as ulimit-n. Then, adjust the process-related parameters based on the server capabilities.

502 is not easy.