It depends on your purpose. If just a standby DC, using GMU to sync policies and relevant configuration regularly should be enough. If you need some kind of active-active HA, you may have to configure DB replication between different DC, that's rarely a good practice unless you have very good network (for example, the latency is less than 10ms). We have a document for it, I will attach it for your consideration. Again, think of the network env before you implement it.