[ClusterLabs] Two node cluster without fencing and no split brain?

[Frank D. Engel, Jr.]

OpenVMS can do this sort of thing without a requirement for fencing (you 
still need a third disk as a quorum device in a 2-node cluster), but 
Linux (at least in its current form) cannot. From what I can tell the 
fencing requirements in the Linux solution are mainly due to limitations 
of how deeply the clustering solution is integrated into the kernel.

There is an overview here: 
https://sciinc.com/remotedba/techinfo/tech_presentations/Boot%20Camp%202013/Bootcamp_2013_Comparison%20of%20Red%20Hat%20Clusters%20with%20OpenVMS%20Clusters.pdf


I am wondering how much of what OpenVMS does could be integrated into 
Linux in the future to simplify the HA clustering situation. This is one 
thing OpenVMS currently does FAR better than any other platform I've 
come across, so it is likely there is still much to be learned from it.


On 7/20/21 6:45 PM, Digimer wrote:
> On 2021-07-20 6:04 p.m., john tillman wrote:
>> Greetings,
>>
>> Is it possible to configure a two node cluster (pacemaker 2.0) without
>> fencing and avoid split brain?
> No.
>
>> I was hoping there was a way to use a 3rd node's ip address, like from a
>> network switch, as a tie breaker to provide quorum.  A simple successful
>> ping would do it.
> Quorum is a different concept and doesn't remove the need for fencing.
>
>> I realize that this 'ping' approach is not the bullet proof solution that
>> fencing would provide.  However, it may be an improvement over two nodes
>> alone.
> It would be, at best, a false sense of security.
>
>> Is there a configuration like that already?  Any other ideas?
>>
>> Pointers to useful documents/discussions on avoiding split brain with two
>> node clusters would be welcome.
> https://www.alteeve.com/w/The_2-Node_Myth
>
> (note: currently throwing a cert error related to the let's encrypt
> issue, should be cleared up soon).
>