[ClusterLabs] VirtualDomain & parallel shutdown

[Jan Pokorný]

On 27/11/18 12:29 +0200, Klecho wrote:
> Big thanks for the answer, but I in your ways around I don't see a solution
> for the following simple case:
> 
> I have a few VMs (VirtualDomain RA) and just want and to stop a few of them,
> not all.
> 
> While the first VM is shutting down (target-role=stopped), it starts some
> slow update, which could take hours (because of the possible update case,
> stop timeout is very big).
> 
> During these hours of update, no other VM can be stopped at all.
> 
> If this isn't avoidable, this could be a quite big flaw, because it blocks
> basic functionality.

It looks like having transition "leaves", i.e. particular executive
manipulations like stop/start operations, last in order of tens of
minutes and longer is not what's pacemaker design had in mind,
as opposed ot pushing asychronicity to the extreme (at the cost
of complexity of the "orthogonality/non-interference tests",
I think).

But the shutdown procedure can be shortcircuited with possible HA
compromises like this:
- put all the VMs you want to stop into an unmananged state
  (is-managed=false)
- trigger the shutdown independently of the cluster mananagement
- when they are indeed off (as also indicated by crm_mon if the
  monitor operation hasn't been disabled), they can be resurrected
  again when suitable (is-managed=true or dropping that property
  to designate an equivalent default)
can't it?

There is a couple of questions, though, like how to make it that
the particular VM won't be shut down in a standard way, which
would trigger the stated problem again (as mentioned, node
shutdown shall be OK).  Customizing resource agent to become
an active pacemaker observer/influencer beside a purposed
notification mechanism and customization through attributes
and rules feels terribly flawed.

-- 
Nazdar,
Jan (Poki)
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