[Pacemaker] Proposed new stonith topology syntax

[Andrew Beekhof]

On Tue, Jan 24, 2012 at 7:20 AM, Dejan Muhamedagic <dejanmm at fastmail.fm> wrote:
> On Mon, Jan 23, 2012 at 08:55:02AM +1100, Andrew Beekhof wrote:
>> On Sat, Jan 21, 2012 at 12:18 AM, Dejan Muhamedagic <dejanmm at fastmail.fm> wrote:
>> > On Fri, Jan 20, 2012 at 01:09:56PM +1100, Andrew Beekhof wrote:
>> >> On Thu, Jan 19, 2012 at 12:15 AM, Dejan Muhamedagic <dejanmm at fastmail.fm> wrote:
>> >> > On Wed, Jan 18, 2012 at 06:58:20PM +1100, Andrew Beekhof wrote:
>> >> >> 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.
>> >> >
>> >> > OK.
>> >> >
>> >> > [...]
>> >> >
>> >> >> > Is there a possibility to express
>> >> >> > fencing nodes simultaneously?
>> >> >>
>> >> >> No.  Its regular boolean shortcut semantics.
>> >> >
>> >> > As digimer mentioned, it is one common use case, i.e. for hosts
>> >> > with multiple power supplies. So far, we recommended lights-out
>> >> > devices for such hardware configurations and if those are
>> >> > monitored and more or less reliable such a setup should be fine.
>> >> > It would still be good to have a way to express it if some day
>> >> > somebody actually implements it. I guess that the schema can be
>> >> > easily extended by adding a "simultaneous" attribute to the
>> >> > "fencing-rule" element.
>> >>
>> >> So in the example below, you'd want the ability to not just trigger
>> >> the 'disk' and 'network' devices, but the ability to trigger them at
>> >> the same time?
>> >
>> > Right.
>>
>> For any particular reason?  Or just in case?
>
> For nodes with multiple PSU and without (supported) management
> board.

That still doesn't explain why the 'off' commands would need to be
simultaneous though.
To turn the node off, both devices just need to turn the port off...
there's no requirement that this happens simultaneously.

> I think that one of our APC stonith agents can turn more
> than one port off simultaneously.

If they're for the same host and device, then you don't even need this.
Just specify two ports in the host_map.

If they're not for the same host, then they're not even covered by the
same fencing operation and will never be simultaneous.

If they're for the same host but different devices, then at most
you'll get the commands sent in parallel, guaranteeing simultaneous is
near impossible.