[ClusterLabs] 2-Node Cluster Pointless?

Dimitri Maziuk dmaziuk at bmrb.wisc.edu
Mon Apr 17 14:52:38 EDT 2017

On 04/17/2017 01:26 PM, Eric Robinson wrote:

> I'm guessing the surviving node broadcasts a gratuitous arp reply. 

You have to fence one node by physically removing power at which point
you don't have a split brain anymore. In a split brain scenario: two
nodes are up, assuming they both send gratuitous arp, one or the other
will win on the router.

If it's the "wrong" one your customer hits the node that can't provide
the service and gets a 404. If it's the right one, the service is still
available despite the split brain.

If you can't ensure your fencing kills the "wrong" node, then the only
practical difference between that and "proper" fencing with split brain
detection and trimmings is the cost of the latter.

Send an SMS to the sysadmin and have them figure it out. Better still,
pay an extra nickel and buy servers that don't go titsup in the first place.

Dimitri Maziuk
BioMagResBank, UW-Madison -- http://www.bmrb.wisc.edu

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