[Pacemaker] Advisory ordering and "Cannot migrate"

[David Vossel]

----- Original Message -----
> From: "Vladislav Bogdanov" <bubble at hoster-ok.com>
> To: "The Pacemaker cluster resource manager" <pacemaker at oss.clusterlabs.org>
> Sent: Tuesday, May 29, 2012 7:27:12 AM
> Subject: [Pacemaker] Advisory ordering and "Cannot migrate"
> 
> Hi Andrew, David, all,
> 
> It seems that advisory ordering is honored when pengine wants to move
> two advisory-ordered resources in one transition, and one of
> resources
> (then) is migrateable.
> 
> I have advisory ordering configured for two resources, "mgs" and
> "drbd-testfs-stacked":
> 
> order drbd-testfs-stacked-after-mgs 0: mgs:start
> drbd-testfs-stacked:start
> 
> "mgs" is ordinary resource, "drbd-testfs-stacked" is migrateable.
> 
> If both that resources are located on one node, and I request
> shutdown
> of that node, I see:
> pengine[2069]:   notice: check_stack_element: Cannot migrate
> drbd-testfs-stacked due to dependency on mgs (order)
> 
> From what I understand, symmetrical advisory ordering should affect
> resources which are about to be both started or both stopped in one
> transition. That's fine.
> 
> But, should it be honored when one resource is to be moved with
> start/stop while another is to be migrated?

I would expect the constraint to be honored.  What else could we possibly do that would make sense?

If you have the following symmetrical order constraint,

start A then start B
stop B then stop A

, where B can be migrated but A can not.  I would expect B to be stopped before A is allowed to stop regardless if B has be ability to be migrated or not.  If both A and B were to be moved to a different node, and B was migrated instead of stop/started, that would invalidate both sides of the order constraint.

-- Vossel

> Best,
> Vladislav
> 
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