[Pacemaker] Favor one node during stonith?

[Andrey Borzenkov]

В Wed, 13 Aug 2014 08:56:58 -0400
Digimer <lists at alteeve.ca> пишет:

> On 13/08/14 08:37 AM, Andrey Borzenkov wrote:
> > Hi,
> >
> > Sorry for may be basic question, but it is my first Linux HA project.
> >
> > I (will) have two node cluster in active/passive configuration -
> > single application on one node and second as standby; application si
> > implemented as master/slave clone. Is it possible to prioritize node,
> > that have active application? So that in case of split brain passive
> > node gets killed?
> >
> > Usually this is done using staggered delay for fencing requests. I
> > think that it may be possible to implement in pacemaker using rules,
> > but I'm a bit uneasy about how to express it. Rule should select a
> > node where master is currently active, not fixed node.
> >
> > Thank you in advance!
> >
> > -andrei
> 
> Hi Andrei,
> 
>    "Basic questions" is how you avoid mistakes, so please never 
> apologize for asking them. I sure ask my own basic questions... :P
> 
>    First up, a little semantics; "split-brain" is what happens when 
> fencing fails. Your asking what happens when the connection between the 
> nodes break when both nodes are otherwise happy (sometimes called a 
> "partitioning of the cluster", though I don't think there is an official 
> term).
> 
>    You are right in guessing that it is "delay" to set this. You add the 
> attribute 'delay="15"' to the fence method. You put the delay attribute 
> on the node you want to win. Here is an example;
> 
> http://clusterlabs.org/wiki/STONITH_Levels#Configuring_The_Fence_Methods
> 
>    In that example, the node called "pcmk-1" has the 'delay' set, so it 
> will get a 15 second head start in fencing "pcmk-2". It works that way 
> because what it does is tell the cluster "If you want to fence 'pcmk-1', 
> pause for 15 seconds before doing so". So in a 2-node cluster 
> partitioning, both would initiate a fence against the other immediately, 
> but pcmk-2 would pause before fencing pcmk-1, where pcmk-1 would *not* 
> pause before fencing pcmk-2.
> 


It statically assigns priorities to cluster nodes. I need to
dynamically assign higher priority (lower delay) to a node that is
currently running application to ensure that application survives. It
was relatively easy in other cluster products I worked with, but I
cannot figure out how to do it in pacemaker so far.

regards,

-andrei