System Administration Guide: Security Services

The Number of Slave KDCs

Slave KDCs generate credentials for clients just as the master KDC does. Slave KDCs provide backup if the master becomes unavailable. Each realm should have at least one slave KDC. Additional slave KDCs might be required, depending on these factors:

It is possible to add too many slave KDCs. Remember that the KDC database must be propagated to each server, so the more KDC servers that are installed, the longer it can take to get the data updated throughout the realm. Also, because each slave retains a copy of the KDC database, more slaves increase the risk of a security breach.

In addition, one or more slave KDCs can easily be configured to be swapped with the master KDC. The advantage of configuring at least one slave KDC in this way is that if the master KDC fails for any reason, you will have a system preconfigured that will be easy to swap as the master KDC. For instructions on how to configure a swappable slave KDC, see Swapping a Master KDC and a Slave KDC.