apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/service/ClusterService.java/ClusterService/delete
class ClusterService:  @Transactional
  public void delete(long id, String operator) {
    Cluster cluster = clusterRepository.findById(id).orElse(null);
    if (cluster == null) {
      throw new BadRequestException("cluster not exist");
    }

    //delete linked namespaces
    namespaceService.deleteByAppIdAndClusterName(cluster.getAppId(), cluster.getName(), operator);

    cluster.setDeleted(true);
    cluster.setDataChangeLastModifiedBy(operator);
    clusterRepository.save(cluster);

    auditService.audit(Cluster.class.getSimpleName(), id, Audit.OP.DELETE, operator);
  }