Symptoms
Some operation from BA control panel results in Service Unavailable error. It can be any kind of operation - subscriptions synchronization, downloading of some big PDF document, accessing TTS ticket queue, etc
Cause
Service Unavailable error does not mean an exception from application side, it is apache timeout. An error means that an operation took more time than default timeout specified in httpd configuration.
Resolution
Check if is is ok that an operation takes more time than apache timeout. If there are reasons (huge set of data for example), timeout can be adjusted.
Check that you are on a correct host (OA UI or Branding, NG), in /var/log/httpd/error_log there shall be a record similar to
[Wed Jun 08 05:33:10 2016] [error] [client 2.2.1.6] (70007)The timeout specified has expired: proxy: error reading status line from remote server hostname.com, referer: https://<...>
[Wed Jun 08 05:33:10 2016] [error] [client 2.2.1.6] proxy: Error reading from remote server returned by /bss-www/sudo..., referer: https://...
Check timeout
[root@name ~]# less /etc/httpd/conf/httpd.conf | grep -i '^timeout'
Timeout 30
Set Timeout to higher value, and reload apache config:
# vi /etc/httpd/conf/httpd.conf
# /etc/init.d/httpd reload
In case of NG cluster, check the /etc/httpd/conf.d/ng_custom.conf in all NG cluster and increase timeout, then reload the httpd service.