[Pacemaker] Proposed new stonith topology syntax

[Andrew Beekhof]

On Thu, Jan 19, 2012 at 12:15 AM, Dejan Muhamedagic <dejanmm at fastmail.fm> wrote:
> On Wed, Jan 18, 2012 at 06:58:20PM +1100, Andrew Beekhof wrote:
>> On Wed, Jan 18, 2012 at 6:00 AM, Dejan Muhamedagic <dejanmm at fastmail.fm> wrote:
>> > Hello,
>> >
>> > On Tue, Jan 03, 2012 at 05:19:14PM +1100, Andrew Beekhof wrote:
>> >> Does anyone have an opinion on the following schema and example?
>> >> I'm not a huge fan of the index field, but nor am I of making it
>> >> sensitive to order (like groups).
>> >
>> > What is wrong with order in XML elements? It seems like a very
>> > clear way to express order to me.
>>
>> Because we end up with the same update issues as for groups.
>
> OK.
>
> [...]
>
>> > Is there a possibility to express
>> > fencing nodes simultaneously?
>>
>> No.  Its regular boolean shortcut semantics.
>
> As digimer mentioned, it is one common use case, i.e. for hosts
> with multiple power supplies. So far, we recommended lights-out
> devices for such hardware configurations and if those are
> monitored and more or less reliable such a setup should be fine.
> It would still be good to have a way to express it if some day
> somebody actually implements it. I guess that the schema can be
> easily extended by adding a "simultaneous" attribute to the
> "fencing-rule" element.

So in the example below, you'd want the ability to not just trigger
the 'disk' and 'network' devices, but the ability to trigger them at
the same time?

>
>> >> Most people will /NOT/ need to add this section to their configuration.
>> >>
>> >> -- Andrew
>> >>
>> >> <fencing-topology>
>> >>   <!-- pcmk-0 requires the devices named disk + network to complete -->
>> >>   <fencing-rule id="f-p0" node="pcmk-0">
>> >>     <device id-ref="disk"/>
>> >>     <device id-ref="network"/>
>> >>   </fencing-rule>
>> >>
>> >>   <!-- pcmk-1 needs either the poison-pill or power device to complete
>> >> successfully -->
>> >>   <fencing-rule id="f-p1.1" node="pcmk-1" index="1" device="poison-pill"/>
>> >>   <fencing-rule id="f-p1.2" node="pcmk-1" index="2" device="power">
>> >>
>> >>   <!-- pcmk-1 needs either the disk and network devices to complete
>> >> successfully OR the device named power -->
>> >>   <fencing-rule id="f-p2.1" node="pcmk-2" index="1">
>> >>     <device id-ref="disk"/>
>> >>     <device id-ref="network"/>
>> >>   </fencing-rule>
>> >>   <fencing-rule id="f-p2.2" node="pcmk-2" index="2" device="power"/>
>> >>
>> >> </fencing-topology>
>> >>
>> >> Conforming to:
>> >>
>> >>   <define name="element-stonith">
>> >>     <element name="fencing-topology">
>> >>       <zeroOrMore>
>> >>       <ref name="element-fencing"/>
>> >>       </zeroOrMore>
>> >>     </element>
>> >>   </define>
>> >>
>> >>   <define name="element-fencing">
>> >>     <element name="fencing-rule">
>> >>       <attribute name="id"><data type="ID"/></attribute>
>> >>       <attribute name="node"><text/></attribute>
>> >>       <attribute name="index"><text/></attribute>
>> >>       <choice>
>> >>       <attribute name="device"><text/></attribute>
>> >>       <zeroOrMore>
>> >>         <element name="device">
>> >>           <attribute name="id-ref"><data type="IDREF"/></attribute>
>> >>         </element>
>> >>       </zeroOrMore>
>> >>       </choice>
>> >>     </element>
>> >>   </define>
>> >
>> > I'd rather use "stonith-resource" than "device", because what is
>> > referenced is a stonith resource (one device may be used in more
>> > than one stonith resource).
>>
>> Can you rephrase that? I don't follow.  Are you talking about a group
>> of fencing devices?
>
> No, just about naming. The element/attribute name "device"
> doesn't seem right to me, because it references a stonith
> resource. One (physical) device may be used by more than one
> stonith resource. Even though "device" certainly sounds nicer,
> it isn't precise.

Oh, I see what you mean.  I'll see what I can come up with.

> What I'm worried about is that it may be
> confusing (and we have enough confusion with stonith).
> (Or did I completely misunderstand the meaning of "device"?)
>
> Thanks,
>
> Dejan
>
>> > Or "stonith-rsc" if you're in the
>> > shortcuts mood. Or perhaps even "agent".
>> >
>> > "fencing-rule" for whatever reason doesn't sound just right, but
>> > I have no alternative suggestion.
>>
>> Agreed.
>>
>> >
>> > IMO, as I already said earlier, index is superfluous.
>> >
>> > It could also be helpful to consider multiple nodes in a single
>> > element.
>> >
>> > Otherwise, looks fine to me.
>> >
>> > Thanks,
>> >
>> > Dejan
>> >
>> >> </grammar>
>> >>
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