Nginx 502 Bad Gateway Error

[G1bsoN]

Hi!
I use Plesk Panel 11.5.30 on Centos 6.5 x86_64 with nginx as a proxy.
Customers can see "502 Bad Gateway" sometimes, and I see this in my logs:
/var/log/nginx/error.log:

2014/10/06 12:00:14 [error] 7642#0: *1557 connect() failed (111: Connection refused) while connecting to upstream, client: 82.137.166.136, server: userdomain.com, request: "GET /askfm/index.php HTTP/1.1", upstream: "http://mypleskip:7080/askfm/index.php", host: "userdomain.com", referrer: "http://userdomain.com/askfm"

In this moment in /var/log/http/error_log

[Mon Oct 06 12:00:12 2014] [notice] caught SIGTERM, shutting down
[Mon Oct 06 12:00:14 2014] [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[Mon Oct 06 12:00:15 2014] [notice] Apache/2.2.15 (Unix) DAV/2 mod_fcgid/2.3.9 mod_jk/1.2.37 mod_python/3.3.1 Python/2.6.6 mod_ssl/2.2.15 OpenSSL/1.0.1e-fips mod_perl/2.0.4 Perl/v5.10.1 configured -- resuming normal operations

Which means that Apache is normally restarted by Plesk if one of a customers make some changes on his domain.
This situation looks normally for me, but it's unacceptable for customers! This makes customer think, that server is fault and hosting is unstable!

I tried to find solution of this problem in kb articles and here, but i didn't find anything. Here http://talk.plesk.com/threads/nginx-502-bad-gateway.312640/ is the same trouble, but there is no answer...
Did anybody found the solution of this problem?

 

[IgorG]

Have you tried to increase the FastCGI buffer size to resolve the issue as below?

# cat /etc/sw-cp-server/config|grep 'fastcgi_buffer'
fastcgi_buffers 128 2048k;
fastcgi_buffer_size 2048k;

 

[G1bsoN]

Have you tried to increase the FastCGI buffer size to resolve the issue as below?

Yes, I tried, but it didn't help.
And if I remember correctly, sw-cp-server - it is a plesk panel gui... I'm sorry if I describe the problem not enough clear.
Error "502 Bad Gateway" nginx shows on customers sites hosted in my Plesk Panel, not in customer CP.

 

[Somebody1]

G1bsoN, you're not alone. Since my system last updated, I'm expierencing this issues as well...

It worked great before...

Edit: I'm using Plesk 12.0.18 though...

 

[G1bsoN]

G1bsoN, you're not alone. Since my system last updated, I'm expierencing this issues as well...

It worked great before...

Edit: I'm using Plesk 12.0.18 though...

Somebody1, have you created ticket to tech support?