this seems rather dangerous to me actually  if we start expecting that the display name that we give to the instance is in dns  and we do not fail the operation if we cannot satisfy that  then users have the potential to do insecure things without realizing  for example nova boot foo ssh  u myuser foo provider com accept host key  y ssh password for myuser foo provider com permission denied ssh password for myuser foo provider com and thus i have just given my password to someone who guessed the hostname that i wanted  unless we expose the actual hostname back to the nova user somehow  we cannot really blame someone for committing the above offense  imho  which is pretty bad 