1.2. A Three-Tier Load Balancer Add-On Configuration
This configuration is ideal for busy FTP servers, where accessible data is stored on a central, highly available server and accessed by each real server via an exported NFS directory or Samba share. This topology is also recommended for websites that access a central, highly available database for transactions. Additionally, using an active-active configuration with Red Hat Cluster Manager, administrators can configure one high-availability cluster to serve both of these roles simultaneously.
The third tier in the above example does not have to use Red Hat Cluster Manager, but failing to use a highly available solution would introduce a critical single point of failure.