Excerpts from Brett Watson's message of 2012-03-13 23:31:10 -0700:
I'm currently planning a shift in our use of LDAP to incorporate mirror mode masters for the sake of high availability. The plan is to hide a mirror mode master pair behind a virtual IP using "sorry server" fail-over, such that the primary mirror server takes 100% of the load when it's up and responsive, with fall-back to the secondary mirror server when the primary is down. In this way, the virtual IP presents a "virtual master" to the outside world, and the plan is for *all* outside LDAP interaction with the masters to happen over this single virtual IP.
There will be other "slave" servers which replicate the master (to distribute read-only load), and the plan is for them to syncrepl from the master virtual IP. I gather that a possible alternative to this arrangement is to have the "slave" servers act as syncrepl consumers to *both* masters simultaneously, via their real IP addresses. If this is indeed a valid configuration, does it convey any advantages? The single "virtual master" approach seems architecturally simpler, but is it considered robust by those in the know?
At my site, the replicas are configured to consume updates directly from both masters simultaneously, bypassing the VIP used by other traffic. Configuring replicas to bypass the VIP means that replication and replica consistency aren't dependent on the failover behavior of the VIP, which makes it easier to reason accurately about the impact of a failure.
Our mirrormode setup is essentially the one you propose for your site, and it works well for our needs.