[Pacemaker] Handling multiple attribute sets (cs#26435fdfd488)

[Dejan Muhamedagic]

Hi,

On Wed, Mar 10, 2010 at 04:24:16PM +0100, Lars Marowsky-Bree wrote:
> Hi all, Dejan,
> 
> the above changeset aims to improve the behaviour with multiple
> attribute sets - right now, the crm_resource et al complain that they
> can't figure out which one to set, so the changeset simply
> clears/updates all of them.
> 
> I disagree, for the following reasons:
> 
> First, I frequently have a "stop" attribute set on a specific resource
> within a group to make the group start up only to that point; I don't
> want that overwritten automatically. In fact, I might just want to
> modify the group target-role, regardless of the value of its children.

Yes, you might, but why don't then just modify the target-role
attribute. I have been thinking about this too and to me

# crm resource start g

seems to express clear intent to start the whole group g. Don't
forget that our minds are plagued by all the technical details
about how the CIB is implemented.

> Second, the instance attribute sets might be subject to different rules;
> overwriting the attribute in all of them would be wrong.

I'd agree on this one in general, though it would probably be
safe in most cases. Unfortunately, there's no way for the shell
to know which particular attribute set may be currently in use
and if they are intended to be used at different times or under
different circumstances. Now, if the administrator has such a
setup, perhaps they should pay due attention.

> I fear if the admin has created the situation of conflicting attribute
> sets, it is the admins responsibility to a) remove them, or b) select
> the specific attribute set they want modified.

True. It's just that the recent stampede of people running into
this issue indicated that something may not exactly be right
here.

> I can see that a) would be supportable by a special command to clear the
> target-role (or possibly any attribute) of children.
> 
> And both a) or b) might be offered as choices in the shell's interactive
> mode.
> 
> But always automatically chosing 'a' seems wrong, and at least took me
> by surprise.

Sorry about that. I hate making software surprise people.

OK, probably a better and more correct way is to offer a choice
in case there are multiple target-roles found. Though that would
probably make quite a narative of a single question ;-) Another
solution could be to keep the old behaviour and introduce a new
option/command form to do a "stop regardless of multiple sets and
what have you". BTW, it is interesting (and funny) that most
admins have no idea about multiple attribute sets :)

Cheers,

Dejan

> Any comments?
> 
> 
> Regards,
>     Lars
> 
> -- 
> Architect Storage/HA, OPS Engineering, Novell, Inc.
> SUSE LINUX Products GmbH, GF: Markus Rex, HRB 16746 (AG Nürnberg)
> "Experience is the name everyone gives to their mistakes." -- Oscar Wilde
> 
> 
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