[ClusterLabs] Fencing explanation

[Ken Gaillot]

I'm not sure Ignazio is talking about an intentional delay. I think his
question may be about node loss detection.

That is done at the Corosync level. See the corosync.conf(5) man page
for all the possible ways it can be configured, but the most important
parameter is "token".

Fencing can also be initiated by Pacemaker for failed resource stops,
or any failed action where on-fail has been set to fence. That
detection time should be bounded by the action timeout, and for
recurring monitors the interval.

On Mon, 2021-01-04 at 11:11 +0100, Klaus Wenninger wrote:
> On 12/29/20 12:38 AM, Reid Wahl wrote:
> > Hi, Ignazio. You can set either the delay in one of two ways:
> > - Using the `delay` attribute, whose value is a bare integer
> > (representing the number of seconds). This is implemented within
> > the
> > fencing library (/usr/share/fence/fencing.py).
> > - Using the `pcmk_delay_base` attribute, whose value is more
> > flexible
> > (e.g., "60", "60s", "1m") as shown below. This is implemented
> > within
> > Pacemaker's fencer component.
> > 
> >  * \param[in] input  Pacemaker time interval specification (a bare
> > number of
> >  *                   seconds, a number with a unit optionally with
> > whitespace
> >  *                   before and/or after the number, or an ISO 8601
> > duration)
> > 
> > In practice, I don't believe it matters which one you use. I see
> > the
> > `delay` attribute used more commonly than the `pcmk_delay_base`
> > attribute.
> 
> Guess this is mainly for historic reasons.
> But there are basically 3 reasons why pcmk_delay_base
> should be preferred:
> 
> 
> - can be used with all ways of fencing
>   not just RHCS-style fence-agents
> - if the fencing-infrastructure knows that no
>   sub-process - running the fence-agent - has been started yet
>   it is easier to handle a termination
> - if combined with a random delay you get a delay that varies
>   between pcmk_delay_base and pcmk_delay_max which is more
>   comprehensible than with using the delay in fencing library
>   where the effective delay would derive to something between
>   {delay define via fencing library} and
>   pcmk_delay_max + {delay defined via fencing library}
> 
> 
> Regards,
> Klaus
> > 
> > For some additional info:
> > - Table 13.1. Additional Properties of Fencing Resources
> > (
> > https://clusterlabs.org/pacemaker/doc/en-US/Pacemaker/1.1/html-single/Pacemaker_Explained/index.html#idm140583403103104
> > )
> > 
> > On Mon, Dec 28, 2020 at 1:22 PM Ignazio Cassano
> > <ignaziocassano at gmail.com> wrote:
> > > Hello all, I am setting a pacemaker cluster with centos 7 and
> > > ipmi idrac fencing devices.
> > > What I did not understand is how set the number of seconds before
> > > a node is rebooted by stonith.
> > > If the cluster is made up 3 nodes (A, B, C) if the node C is
> > > unreacheable (for example have network cards corrupetd) after how
> > > many second is rebooted by stonith ?
> > > Which is the parameter to set the number of seconds?
> > > Sorry for my bad english
> > > Thanks
> > > Ignazio
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> 
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-- 
Ken Gaillot <kgaillot at redhat.com>