Why do we need odd number of NSX Controllers when there is NSX Manager?

[apenkontap]

Hi,

I would like to ask a question regarding NSX controller split brain scenario.

Why do we need an odd number of NSX Controllers (3 or 5) ?

If it for quorum requirement, then why don't NSX use NSX Manager as the quorum / third party?

Thank you.

Apenk

[mtmtkm]

Hi.

Why do we need an odd number of NSX Controllers (3 or 5) ?

Controllers need to be odd number because otherwise it cannot break ties in split brain scenario.

e.g. if the number is 3 and 1 fails, then other 2 needs to be the same state to continue working so that more then 50% of controllers agreed to operate. It won't work if it's only 1 left.

But more important thing is that only 3 controllers are supported on NSX for vSphere now.

If it for quorum requirement, then why don't NSX use NSX Manager as the quorum / third party?

I have no answer for it, but NSX manager is Management Plane and NSX Controllers are Control Plane so they do different things.

Thank you,

[bayupw]

VMware NSX Controller uses Paxos-based algorithm within NSX Controller cluster Paxos (computer science) - Wikipedia, the free encyclopedia

There's also a good blog by Roie Ben Haim roie9876‌ that explains more about how nsx controller works in overview and some troubleshooting guidance

http://www.routetocloud.com/2014/11/troubleshooting-nsx-v-controller/