apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/service/AppNamespaceService.java/AppNamespaceService/createNamespaceForAppNamespaceInAllCluster
class AppNamespaceService:  public void createNamespaceForAppNamespaceInAllCluster(String appId, String namespaceName, String createBy) {
    List<Cluster> clusters = clusterService.findParentClusters(appId);

    for (Cluster cluster : clusters) {

      // in case there is some dirty data, e.g. public namespace deleted in other app and now created in this app
      if (!namespaceService.isNamespaceUnique(appId, cluster.getName(), namespaceName)) {
        continue;
      }

      Namespace namespace = new Namespace();
      namespace.setClusterName(cluster.getName());
      namespace.setAppId(appId);
      namespace.setNamespaceName(namespaceName);
      namespace.setDataChangeCreatedBy(createBy);
      namespace.setDataChangeLastModifiedBy(createBy);

      namespaceService.save(namespace);
    }
  }