apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/service/ClusterService.java/ClusterService/createCluster
class ClusterService:  public ClusterDTO createCluster(Env env, ClusterDTO cluster) {
    if (!clusterAPI.isClusterUnique(cluster.getAppId(), env, cluster.getName())) {
      throw new BadRequestException(String.format("cluster %s already exists.", cluster.getName()));
    }
    ClusterDTO clusterDTO = clusterAPI.create(env, cluster);

    Tracer.logEvent(TracerEventType.CREATE_CLUSTER, cluster.getAppId(), "0", cluster.getName());

    return clusterDTO;
  }