This is a non-rebuild situation, like when Foreman triggers an update to the host group.
'random' isn't valid for a host that has a keytab, and it will throw an exception. 

"Nothing to do" is yet another use case: when Foreman triggers an update but doesn't actually update anything (say, user changed the host group and changed it immediately back).  It also throws an exception. 

The XMLRPC API loves exceptions.