If you explicitly define your host into the sudo rule, does it work? Can you post the
output with the hostname explicitly defined in the rule, to see if it parses it? That way
we can at least see if sudo is comparing it's FQDN to what's in the host rule.
if it does find the host, then it means the issue lies with hostgroup expansion. If it
doesn't then the issue lies with how sudo is interpreting the name of server and
comparing. We need to first see if sudo is properly comparing it's name to what it