Hi,
Cisco ACS has a replication feature that allows you to have more than one (1) ACS servers/appliances to provide high-availability/ redundancy. In this case, you will have one primary and more than one secondary (backup) servers.
The database replication creates mirror systems of ACSs by duplicating parts of the primary ACS setup to one or more secondary ACSs. Without load-balancer, you need to add both primary and secondary ACSs in all AAA clients as backup if the primary ACS fails or is unreachable. With a secondary ACS whose ACS internal database is a replica of the ACS internal database on the primary ACS, if the primary ACS goes out of service, incoming requests are authenticated without network downtime, provided that your AAA clients are configured to fail over to the secondary ACS.
The following url provides you with details on how the ACS replication is performed:
http://www.cisco.com/univercd/cc/td/doc/product/access/acs_soft/csacs4nt/acs40/user/sad.htm#wp756102
http://www.cisco.com/univercd/cc/td/doc/product/access/acs_soft/csacs4nt/acs40/user/index.htm
I am not sure about load-balancing two ACSs, but you probably can try this. Behind a load-balancer, maintain the primary/secondary server setup to enable replication (selected items only) from primary to secondary ACS. But pls bear in mind, in replication, only the Primary ACS can send update to backup server, not bidirectional. Backup/secondary ACS can only receive updates. Use the replication features as an update tool between the servers. All changes/updates must be made in your primary ACS only.
In normal ACS replication, all AAA clients need to specify primary and secondary ACS server as backup. With load-balancer, only one (1) IP need is required, which is the virtual IP assigned by load-balancer to represent the two ACSs.
Rgds,
AK
