[Pacemaker] crm shell and collocating sets

[Dejan Muhamedagic]

On Mon, Jan 24, 2011 at 10:56:40AM -0500, Vadym Chepkov wrote:
> On Mon, Jan 24, 2011 at 10:41 AM, Dejan Muhamedagic <dejanmm at fastmail.fm> wrote:
> > Hi,
> >
> > On Sat, Jan 22, 2011 at 01:38:12PM -0500, Vadym Chepkov wrote:
> >> Hi,
> >>
> >> It seems crm shell can't express sequential="true" in  collocating sets, which is strange, since, I assume, it's a default.
> >>
> >> If you load an example using cibadmin from "Configuration explained"
> >>
> >> Example 6.16. Using colocation sets to specify a common peer.
> >>   <constraints>
> >>     <rsc_colocation id="coloc-1" score="INFINITY" >
> >>       <resource_set id="collocated-set-1" sequential="false">
> >>         <resource_ref id="A"/>
> >>         <resource_ref id="B"/>
> >>         <resource_ref id="C"/>
> >>       </resource_set>
> >>       <resource_set id="collocated-set-2" sequential="true">
> >>         <resource_ref id="D"/>
> >>       </resource_set>
> >>     </rsc_colocation>
> >>   </constraints>
> >>
> >>
> >> It will look like this in crm configure show output:
> >>
> >> xml <rsc_colocation id="coloc-1" score="INFINITY"> \
> >>       <resource_set id="collocated-set-1" sequential="false"> \
> >>               <resource_ref id="A"/> \
> >>               <resource_ref id="B"/> \
> >>               <resource_ref id="C"/> \
> >>       </resource_set> \
> >>       <resource_set id="collocated-set-2" sequential="true"> \
> >>               <resource_ref id="D"/> \
> >>       </resource_set> \
> >> </rsc_colocation>
> >>
> >> Not exactly a "simplification"
> >>
> >> Am I missing something? How one would express the same constraint using shell?
> >
> > By omitting sequential="true". The problem is that two XML
> > representation have the same meaning, but look slightly
> > different, which again makes shell think that it could've done
> > something wrong while rendering XML from the CLI presentation.
> >
> > Anyway, that should be fixed somehow.
> >
> > Thanks,
> >
> > Dejan
> 
> If you ever consider do something about it, here is another thing that
> can be lived with, but is non-intuitive.
> 
> 1) colocation c1 inf: A B
> 
> the most significant is B (if B is stopped nothing else will be running)
> 
> 2) colocation c2 inf: A B C
> 
> most significant - A
> 
> 3) colocation c3 inf: ( A B ) C
> 
> most significant - C
> 
> 4) colocation c4 inf: ( A B ) C D
> 
> most significant - C again
> 
> I am trying to find a logic to remember this, but fails so far :)

No wonder. I have a patch ready to fix this, but have never been
happy with it.

Resources within a resource set have opposite semantics to 2-rsc
collocations. But two adjacent resource sets are again as 2-rsc
collocations, i.e. the left set follows the right set. Now,
just to add to the confusion, in the example 4) above it is not
very obvious that there are two sets, and that the second set is
"C D". So, 4) should be equivalent to these 5 2-rsc collocations:

A C
B C
A D
B D
D C

What is the difference (if any) of the above to

A D
B D
D C

Well, we leave that to the interested as an exercise ;-)

Thanks,

Dejan

> Thanks,
> Vadym
> 
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