OpenSSH + Kerberos SSO: No key table entry found for host/localhost.localdomain

Could be a simple host name issue or a domain realm mapping issue.
(It's probably the first one, but for completeness here are both.)

hostname issue
hostname -f on kerberos.monzell.com
should return: kerberos.monzell.com
should not return: localhost.localdomain

domain realm mapping issue
dig -t txt _kerberos.kerberos.monzell.com
dig -t txt _kerberos.monzell.com

If you don't want to use /etc/krb5.conf should return
<record> <ttl num> IN TXT "MONZELL.COM".

However, given hosts file this is probably not the case.
/etc/krb5.conf should contain either:

[domain_realm]
.monzell.com MONZELL.COM

or

[domain_realm]
kerberos.monzell.com MONZELL.COM