Do you see any error in the logs?
Also do you have the garbage collection logs of the jboss instances.
When you see the service unavailable messages that time did you notice the JBoss logs for any error/warn? If it is hanged or responding slow then collect 5-6 thread dumps to see the thread activities.
I added categories org.jboss.web, org.jboss.security, org.jboss.ha, org.jboss.cache,org.jboss.as.web.sso and org.jboss.as.config, set level to trace, but i dont see nothing weird.
How do i set up garbage collection logs? On apache logs i got some errors like "cant read node" errors.
It seems that when we do a ssh and connect to the jboss domain node host, it starts working, could be SELinux related?
GC logging is simple to activate, Use a search with "enable gc logging", a hit will be https://confluence.atlassian.com/display/CONFKB/Enable+Garbage+Collection+Logging
Do you have a very simpe test app deployed? Did this work? Maybe you deploy this app in case of the problem and try to see whether it gest deployed and accessable.
In this case GC and JBoss seems working. Than you need to look for the environment like LDAP etc.