how could deploy backup keystone service across multiple region

In my situation, there are three Openstack clusters deployed at three different cities which called regionA, regionB and regionC. - We use the one keystone service which is only deployed in regionA. - Now we should deploy the keystone backup service at regionC, this regionC keystone is only for backup or using while regionA keystone shutdown. How could I achieve that? In my opinion, we should deploy the databases like MariaDB and Keystone service at regionC, but I can't figure out how to do, this reference "Multiple Regions Deployment with Kolla " can't solve my problem