[Pacemaker] Proposed new stonith topology syntax

[Dejan Muhamedagic]

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.

> >> 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. 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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