gistfile1.txt

Added respective exceptions in nova/exception.py

nova/service.py
        try:
            self.servicegroup_api.start(self.host)
        except exception.ToozBackendConnectionError:
            msg = _("Error connecting to coordination backend")
            raise exc.HTTPServiceUnavailable(explanation=msg)
        except exception.ToozBackendUrlFormatNotsupported:
            msg = _("Tooz Backend url format not supported)
            raise exc.HTTPBadRequest(explanation=msg)
            
            
            
            
tz.py            
def start(self, member_id):$
        backend_url = cfg.CONF.coordination.backend_url$
        try:$
            self._coordinator = tooz.coordination.get_coordinator($
                backend_url, member_id)$
            self._coordinator.start()$
            self._started = True$
            LOG.info(_LI('Coordination backend started successfully'))$
        except tooz.coordination.ToozError:$
            self._started = False$
            LOG.exception(_LE('Error connecting to coordination backend'))$
            raise exception.ToozBackendConnectionError()$
        except RuntimeError:$
            self._started = False$
            raise exception.ToozBackendUrlFormatNotsupported()$