Clustering of vRealize Orchestrator is moved from the Control Center to the VAMI. Since version 7.5, you not only cluster the vRO application, but also the embedded database. To start configuring it you need to login to one of your appliances on port 5480 (https://vro-appliance_ip_or_fqdn:5480). For login, you must use the root account and its password. The one you set during the deployment. In case you don’t remember it, you can reset it by following the steps from this KB article.
Before you start configuring the cluster, be sure you have proper time source configured on all vRO appliances.
To start, you need to go at the Cluster tab and enter the FQDN (preferably if you have DNS access) to the Leadining Cluster Node field, followed by Admin User and Password for the destination vRO. After entering this information, you should click Join Cluster.
Repeat this step on each of the additional nodes you want to add to the cluster.
By default, regardless of the number of the vRO appliances, the database replication mode is set to Asynchronous Mode. If you want to have an automatic failover for the database, not only for the vRO application, you need minimum 3 nodes. Once you have them configured in a cluster, you can change the mode by selecting Sync Mode.
On application level, by default all vROs will be set to Running state. Even the DB is being set to Sync Mode, you can still create an Active-Standby cluster from the control center.
If the DB synchronization mode is set to Synchronous, you can always change it back to Async if you want.
I hope this was useful. Cheers!