[ClusterLabs] How Pacemaker reacts to fast changes of the same parameter in configuration

[Dejan Muhamedagic]

On Tue, Nov 08, 2016 at 12:54:10PM +0100, Klaus Wenninger wrote:
> On 11/08/2016 11:40 AM, Kostiantyn Ponomarenko wrote:
> > Hi,
> >
> > I need a way to do a manual fail-back on demand.
> > To be clear, I don't want it to be ON/OFF; I want it to be more like
> > "one shot".
> > So far I found that the most reasonable way to do it - is to set
> > "resource stickiness" to a different value, and then set it back to
> > what it was. 
> > To do that I created a simple script with two lines:
> >
> >     crm configure rsc_defaults resource-stickiness=50
> >     crm configure rsc_defaults resource-stickiness=150
> >
> > There are no timeouts before setting the original value back.
> > If I call this script, I get what I want - Pacemaker moves resources
> > to their preferred locations, and "resource stickiness" is set back to
> > its original value. 
> >
> > Despite it works, I still have few concerns about this approach.
> > Will I get the same behavior under a big load with delays on systems
> > in cluster (which is truly possible and a normal case in my environment)?
> > How Pacemaker treats fast change of this parameter?
> > I am worried that if "resource stickiness" is set back to its original
> > value to fast, then no fail-back will happen. Is it possible, or I
> > shouldn't worry about it?
> 
> AFAIK pengine is interrupted when calculating a more complicated transition
> and if the situation has changed a transition that is just being executed
> is aborted if the input from pengine changed.
> So I would definitely worry!
> What you could do is to issue 'crm_simulate -Ls' in between and grep for
> an empty transition.
> There might be more elegant ways but that should be safe.

crmsh has an option (-w) to wait for the PE to settle after
committing configuration changes.

Thanks,

Dejan
> 
> > Thank you,
> > Kostia
> >
> >
> > _______________________________________________
> > Users mailing list: Users at clusterlabs.org
> > http://clusterlabs.org/mailman/listinfo/users
> >
> > Project Home: http://www.clusterlabs.org
> > Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
> > Bugs: http://bugs.clusterlabs.org
> 
> 
> 
> _______________________________________________
> Users mailing list: Users at clusterlabs.org
> http://clusterlabs.org/mailman/listinfo/users
> 
> Project Home: http://www.clusterlabs.org
> Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
> Bugs: http://bugs.clusterlabs.org