[Pacemaker] Proposed new stonith topology syntax

[Dejan Muhamedagic]

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.

> Please keep in mind that the new topology section is optional and
> would only be defined if:
>  - you wanted to specify the order in which multiple devices were tried, or
>  - if multiple devices need to be triggered for the node to be
> considered fenced.

Triggered serially I guess? Is there a possibility to express
fencing nodes simultaneously?

> 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). 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.

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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