apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Cluster.java/Cluster/compareTo
class Cluster:  @Override
  public int compareTo(Cluster o) {
    if (o == null || getId() > o.getId()) {
      return 1;
    }

    if (getId() == o.getId()) {
      return 0;
    }

    return -1;
  }