On Wed, 14 Mar 2012, Brett Watson wrote: >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? Thanks in advance. Well, people test this

quite regularly (via OpenLDAP's included test suite) and it seems to work without issue; there are also live sites using mirrormode and (anecdotally) I don't believe they have an excessive defect rate versus other installations. As with most the-other-node-must-be-dead scenarios, the ugly edge cases rest more on the traffic direction methods than the actual application. You'd probably be well served by taking a careful stock of your "virtual IP" methods -- split brain, false positives, what have you -- and OpenLDAP will likely serve you well.

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?