[Pacemaker] Proposed new stonith topology syntax

[Andrew Beekhof]

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.

>
>> 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?

Yes.

> Is there a possibility to express
> fencing nodes simultaneously?

No.  Its regular boolean shortcut semantics.

>> 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?

> 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>
>>
>> _______________________________________________
>> Pacemaker mailing list: Pacemaker at oss.clusterlabs.org
>> http://oss.clusterlabs.org/mailman/listinfo/pacemaker
>>
>> Project Home: http://www.clusterlabs.org
>> Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
>> Bugs: http://bugs.clusterlabs.org
>
> _______________________________________________
> Pacemaker mailing list: Pacemaker at oss.clusterlabs.org
> http://oss.clusterlabs.org/mailman/listinfo/pacemaker
>
> Project Home: http://www.clusterlabs.org
> Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
> Bugs: http://bugs.clusterlabs.org