502 Bad Gateway on Nginx every hour

[Azurel]

I use plesk 11.5.30 #47 on debian 6.5 final (32GB RAM, 1TB HDD)

I restart every hour the apache with a cron (because; I load a new DENY FROM list for apache):

/etc/init.d/httpd graceful

How to make modification take affect without restart nginx?

/var/log/nginx/error.log

2014/06/15 16:01:02 [error] 3567#0: *20319477 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 17:01:02 [error] 3567#0: *20648429 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 19:01:01 [error] 3567#0: *21291185 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 20:01:02 [error] 3567#0: *21651034 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 20:01:02 [error] 3567#0: *21648064 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 21:01:02 [error] 3567#0: *21988202 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 21:01:02 [error] 3567#0: *21985129 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 21:01:02 [error] 3567#0: *21977116 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 21:01:02 [error] 3567#0: *21988211 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 21:01:02 [error] 3567#0: *21987579 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 21:01:02 [error] 3567#0: *21988196 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 21:01:02 [error] 3567#0: *21988205 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 21:01:03 [error] 3567#0: *21983454 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 22:01:02 [error] 3567#0: *22320294 upstream prematurely closed connection while reading response header from upstream, client:
2014/06/15 22:01:02 [error] 3567#0: *22347634 upstream prematurely closed connection while reading response header from upstream, client:

/var/log/httpd/error_log

[Sun Jun 15 20:01:02 2014] [notice] Graceful restart requested, doing restart
[Sun Jun 15 20:01:02 2014] [notice] Digest: generating secret for digest authentication ...
[Sun Jun 15 20:01:02 2014] [notice] Digest: done
[Sun Jun 15 20:01:02 2014] [notice] mod_python: Creating 4 session mutexes based on 750 max processes and 0 max threads.
[Sun Jun 15 20:01:02 2014] [notice] mod_python: using mutex_directory /tmp
[Sun Jun 15 20:01:02 2014] [warn] RSA server certificate CommonName (CN) `Parallels Panel' does NOT match server name!?
[Sun Jun 15 20:01:02 2014] [warn] RSA server certificate CommonName (CN) `Parallels Panel' does NOT match server name!?
[Sun Jun 15 20:01:02 2014] [warn] RSA server certificate CommonName (CN) `Parallels Panel' does NOT match server name!?
[Sun Jun 15 20:01:02 2014] [warn] Init: Name-based SSL virtual hosts only work for clients with TLS server name indication support (RFC 4366)
[Sun Jun 15 20:01:02 2014] [notice] Apache/2.2.15 (Unix) DAV/2 mod_fcgid/2.3.9 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
[Sun Jun 15 21:01:02 2014] [notice] Graceful restart requested, doing restart
[Sun Jun 15 21:01:03 2014] [notice] Digest: generating secret for digest authentication ...
[Sun Jun 15 21:01:03 2014] [notice] Digest: done
[Sun Jun 15 21:01:03 2014] [notice] mod_python: Creating 4 session mutexes based on 750 max processes and 0 max threads.
[Sun Jun 15 21:01:03 2014] [notice] mod_python: using mutex_directory /tmp
[Sun Jun 15 21:01:03 2014] [warn] RSA server certificate CommonName (CN) `Parallels Panel' does NOT match server name!?
[Sun Jun 15 21:01:03 2014] [warn] RSA server certificate CommonName (CN) `Parallels Panel' does NOT match server name!?
[Sun Jun 15 21:01:03 2014] [warn] RSA server certificate CommonName (CN) `Parallels Panel' does NOT match server name!?
[Sun Jun 15 21:01:03 2014] [warn] Init: Name-based SSL virtual hosts only work for clients with TLS server name indication support (RFC 4366)
[Sun Jun 15 21:01:03 2014] [notice] Apache/2.2.15 (Unix) DAV/2 mod_fcgid/2.3.9 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
[Sun Jun 15 22:01:02 2014] [notice] Graceful restart requested, doing restart
[Sun Jun 15 22:01:03 2014] [notice] Digest: generating secret for digest authentication ...
[Sun Jun 15 22:01:03 2014] [notice] Digest: done
[Sun Jun 15 22:01:03 2014] [notice] mod_python: Creating 4 session mutexes based on 750 max processes and 0 max threads.
[Sun Jun 15 22:01:03 2014] [notice] mod_python: using mutex_directory /tmp
[Sun Jun 15 22:01:03 2014] [warn] RSA server certificate CommonName (CN) `Parallels Panel' does NOT match server name!?
[Sun Jun 15 22:01:03 2014] [warn] RSA server certificate CommonName (CN) `Parallels Panel' does NOT match server name!?
[Sun Jun 15 22:01:03 2014] [warn] RSA server certificate CommonName (CN) `Parallels Panel' does NOT match server name!?
[Sun Jun 15 22:01:03 2014] [warn] Init: Name-based SSL virtual hosts only work for clients with TLS server name indication support (RFC 4366)
[Sun Jun 15 22:01:03 2014] [notice] Apache/2.2.15 (Unix) DAV/2 mod_fcgid/2.3.9 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