[Pacemaker] [pacemaker][patch 3/4] Simple changes for "Pacemaker Explained", Chapter 6 CH_Constraints.xml

[Tim Serong]

On 3/21/2011 at 08:20 PM, Andrew Beekhof <andrew at beekhof.net> wrote: 
>  
> Small improvement to: 
> +	The only thing that matters is that in order for any member of a set 
> to be active, all the members of the previous set must also be active 
> (and naturally on the same node). When a set has 
> <literal>sequential="true"</literal>, then in order for any member to 
> be active, the previous members must also be active. 
>  
> +	The only thing that matters is that in order for any member of a set 
> to be active, all the members of the previous set<footnote><para>as 
> determined by the display order in the configuration</para></footnote> 
> must also be active (and naturally on the same node). 
> + When a set has <literal>sequential="true"</literal>, then in order 
> for any member to be active, the previous members must also be active. 

This isn't quite correct.

For members within a set (sequential=true), it is true that for a given
member to be active, the previous members must also be active.

Between sets however, it's the other way around - a given set depends on
the subsequent set.

The example colocation chain in Pacemaker Explained right now should thus
be changed as follows in order to match the diagram:

  <constraints>
    <rsc_colocation id="coloc-1" score="INFINITY" >
       <resource_set id="collocated-set-1" sequential="true">
-        <resource_ref id="A"/>
-        <resource_ref id="B"/>
+        <resource_ref id="F"/>
+        <resource_ref id="G"/>
      </resource_set>
      <resource_set id="collocated-set-2" sequential="false">
        <resource_ref id="C"/>
        <resource_ref id="D"/>
        <resource_ref id="E"/>
      </resource_set>
      <resource_set id="collocated-set-2" sequential="true" role="Master">
-        <resource_ref id="F"/>
-        <resource_ref id="G"/>
+        <resource_ref id="A"/>
+        <resource_ref id="B"/>
      </resource_set>
    </rsc_colocation>
  </constraints>

Regards,

Tim


-- 
Tim Serong <tserong at novell.com>
Senior Clustering Engineer, OPS Engineering, Novell Inc.