No errors in there either ? Strange?
Maybe linked to Apache? I recall this might have started after an update. This link may shed some light ?
https://devcentral.f5.com/questions/502-proxy-error
Some log file from Apache
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1. Set the 'ServerName' directive globally to suppress this message
[Thu Jan 22 14:32:19.788813 2015] [auth_digest:notice] [pid 838] AH01757: generating secret for digest authentication ...
[Thu Jan 22 14:32:19.790420 2015] [lbmethod_heartbeat:notice] [pid 838] AH02282: No slotmem from mod_heartmonitor
[Thu Jan 22 14:32:19.825131 2015] [mpm_prefork:notice] [pid 838] AH00163: Apache/2.4.10 (Fedora) PHP/5.5.19 Phusion_Passenger/3.0.21 configured -- resuming normal operations
[Thu Jan 22 14:32:19.825153 2015] [core:notice] [pid 838] AH00094: Command line: '/usr/sbin/httpd -D FOREGROUND'
[Thu Jan 22 18:34:19.449968 2015] [mpm_prefork:notice] [pid 838] AH00170: caught SIGWINCH, shutting down gracefully
[Thu Jan 22 18:35:23.355573 2015] [suexec:notice] [pid 811] AH01232: suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
AH00557: httpd: apr_sockaddr_info_get() failed for tiger
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1. Set the 'ServerName' directive globally to suppress this message
[Thu Jan 22 18:35:43.508932 2015]
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