'Resolve the hostname for a service in a particular region.
:type service_name: str
:param service_name: The service to look up.
:type region_name: str
:param region_name: The region to find the endpoint for.
:return: The hostname for the given service in the given region.'

def resolve_hostname(self, service_name, region_name):

    endpoint = self._resolver.construct_endpoint(service_name, region_name)
    if (endpoint is None):
        return None
    return endpoint.get('sslCommonName', endpoint['hostname'])
