I encountered the following error when trying to regenerate keytabs. I have recently upgraded from HDP 2.6 to HDP 3.0. I am using FreeIPA. The name of the host of the ambari server is not ambari_server -- I am not sure why it tries to create a new principal HTTP/ambari_server@REALM.
2018-10-09 17:17:00,700 - Failed to create principal, HTTP/ambari_server@ZXCOMPUTERS.COM - Failed to create principal for HTTP/ambari_server@ZXCOMPUTERS.COM
STDERR: ipa: ERROR: The host 'ambari_server' does not exist to add a service to.
2018-10-09 17:17:21,815 - Failed to create principal, - Failed to create new principal - no principal specified
So the "_HOST" is actually replaced with the FQDN of the host. So in your case are you sure that "ambari_server" is the FQDN of your ambari server host ? OR have you recently changed the FQDN of your ambari server host?
Can you please share the output of the following commands from Ambari Server host?