code: def destroyCluster(self):
          
          logger.debug("Destroying cluster %s" % self.clusterName)
          instancesToTerminate = self._getNodesInCluster()
          attempts = 0
          while instancesToTerminate and attempts < 3:
              self._terminateInstances(instances=instancesToTerminate)
              instancesToTerminate = self._getNodesInCluster()
              attempts += 1
  
          # remove group
          instanceGroup = self._gceDriver.ex_get_instancegroup(self.clusterName, zone=self._zone)
          instanceGroup.destroy()
docs: Try a few times to terminate all of the instances in the group.