code: def _pre_heat_deploy(self):
          
          clients = self.app.client_manager
          compute_client = clients.compute
  
          self.log.debug("Checking hypervisor stats")
          if utils.check_hypervisor_stats(compute_client) is None:
              raise exceptions.DeploymentError(
                  "Expected hypervisor stats not met")
          return True
docs: Setup before the Heat stack create or update has been done.