[Pacemaker] Proposed new stonith topology syntax

Dejan Muhamedagic dejanmm at fastmail.fm
Fri Jan 20 13:18:25 UTC 2012 

On Fri, Jan 20, 2012 at 01:09:56PM +1100, Andrew Beekhof wrote:
> 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?

Right.

> >> >> 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.

OK.

Cheers,

Dejan

> > 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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