This Knowledgebase article provides information as to why Neverfail cannot be installed on a Domain Controller.
Neverfail does not replicate the Active Directory partitions from the active to the passive server because these files are in constant use on the passive server.
Neverfail SCOPE will flag a server that is configured as a Domain Controller preventing a license from being issued for the Hardware ID found on the server thereby preventing a successful installation of Neverfail Heartbeat.
The following provides a technical explanation on why Neverfail Heartbeat cannot be installed on a Domain Controller.
- Active Directory FSMO Roles
- Global Catalogues
- The first Domain Controller in the Forest is always a Global Catalogue, unless this role is demoted by an Administrator.
- Any server can be promoted to the Global Catalogue role.
- Replication Intervals & Topology
The Active Directory server cannot host any one of the five Flexible Single Master Operations (FSMO) roles, as the name suggests these roles only exist on one server within the domain, so they must be accurate and up to date. These roles by default are installed on the first Domain Controller within the Forest, however they can be moved to any server. This rules out forests containing a single domain and a single domain controller e.g. Small Business Server.
Another specialized role of an Active Directory server is the Global Catalogue (GC) server. This server contains partial replication information for the whole Forest, there should be a minimum of one per site. Without an accurate record of domain objects, it would fail to service some requests correctly for local clients. Another key responsibility is providing user logon referrals; these may fail if the records are out of date. The Global Catalogue role is assigned to:
Microsoft does not recommend placing both these services on a single server because it creates performance issues and a single point of failure.
When the user base is small enough, Microsoft recommends that the server be prompted to a Global Catalogue server because Exchange queries Global Catalogue constantly e.g. in the case of Small Business Server. Converting the server to a Global Catalogue will then violate item 2 above.
Active Directory topologies containing multiple Domain Controllers, spanning multiple domains and sites create a complicated replication topology, which is unique to every organization. The replication interval depends upon how the Active Directory forest was built, the mode it operates in, the platforms used, the number of servers per site, and the site topology. For more information on Active Directory and replication, please see: