The AD RMS cluster is a single RMS server or a group of servers that share certificates and licensing requests from their clients. Even though it is named as a cluster, it is different from a typical Windows failover cluster term. The failover cluster needs at least two nodes. However, with RMS even though it has single server it becomes a cluster. But there is one requirement for the AD RMS cluster if there are multiple servers involved. AD RMS supports two types of databases similar to AD FS. By default, it uses the Windows Internal Database (WID), and it also supports the Microsoft SQL Server database. If the AD RMS cluster is going to have multiple servers, it must use the MS SQL database on a separate server.

There are two types of clusters in AD RMS:

• The root cluster: When you first set up the AD RMS server in the infrastructure, it becomes the root cluster. By default, it responds to both licensing and certificates requests from clients. When required, additional RMS servers can be added to the cluster. There is only one root cluster that can exist in one AD DS forest.
• Licensing cluster: If an organization has multiple Active Directory sites, there are situations where remote sites prefer to use servers on their own site whenever possible. It prevents users from connecting sites through slow links. In such scenarios, organizations can deploy licensing-only cluster on remote sites. It only responds to licensing requests from clients.

When the new RMS server is added to the infrastructure, based on installed roles, it will automatically make it part of the relevant cluster. However, it is recommended that you use the root cluster only, as it will automatically load balance both certificates and licensing requests. When it has two clusters, load balancing is handled by each cluster separately even though they are components of one system.