code: def validate_linux_host_name(namespace):
      
      # https://stackoverflow.com/questions/106179/regular-expression-to-match-dns-hostname-or-ip-address
      rfc1123_regex = re.compile(r'^([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])(\.([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]{0,61}[a-zA-Z0-9]))*$')  # pylint:disable=line-too-long
      found = rfc1123_regex.findall(namespace.name)
      if not found:
          raise CLIError('--name cannot exceed 63 characters and can only contain '
                         'letters, numbers, or dashes (-).')
docs: Validates a string as a legal host name component.
  
      This validation will also occur server-side in the ARM API, but that may take
      a minute or two before the user sees it. So it's more user-friendly to validate
      in the CLI pre-flight.