apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/api/AdminServiceAPI.java/AdminServiceAPI/isClusterUnique
class AdminServiceAPI:    public boolean isClusterUnique(String appId, Env env, String clusterName) {
      return restTemplate
          .get(env, "apps/{appId}/cluster/{clusterName}/unique", Boolean.class,
              appId, clusterName);

    }