Determine the current usage for each limit of this service,
        and update corresponding Limit via
        :py:meth:`~.AwsLimit._add_current_usage`.

def find_usage(self):
        """
        Determine the current usage for each limit of this service,
        and update corresponding Limit via
        :py:meth:`~.AwsLimit._add_current_usage`.
        """
        logger.debug("Checking usage for service %s", self.service_name)
        self.connect()
        for lim in self.limits.values():
            lim._reset_usage()
        self._find_usage_nodes()
        self._find_usage_subnet_groups()
        self._find_usage_parameter_groups()
        self._find_usage_security_groups()
        self._have_usage = True
        logger.debug("Done checking usage.")