[ClusterLabs] Fencing explanation

Klaus Wenninger kwenning at redhat.com
Mon Jan 4 05:11:11 EST 2021

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}

> 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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