[Pacemaker] Migration of "lower" resource causes dependent resources to restart

[Andrew Beekhof]

On Fri, Mar 30, 2012 at 7:10 PM, Florian Haas <florian at hastexo.com> wrote:
> On Thu, Mar 29, 2012 at 8:35 AM, Andrew Beekhof <andrew at beekhof.net> wrote:
>> On Thu, Mar 29, 2012 at 5:28 PM, Vladislav Bogdanov
>> <bubble at hoster-ok.com> wrote:
>>> Hi Andrew, all,
>>>
>>> Pacemaker restarts resources when resource they depend on (ordering
>>> only, no colocation) is migrated.
>>>
>>> I mean that when I do crm resource migrate lustre, I get
>>>
>>> LogActions: Migrate lustre#011(Started lustre03-left -> lustre04-left)
>>> LogActions: Restart mgs#011(Started lustre01-left)
>>>
>>> I only have one ordering constraint for these two resources:
>>>
>>> order mgs-after-lustre inf: lustre:start mgs:start
>>>
>>> This reminds me what have been with reload in a past (dependent resource
>>> restart when "lower" resource is reloaded).
>>>
>>> Shouldn't this be changed? Migration usually means that service is not
>>> interrupted...
>>
>> Is that strictly true?  Always?
>
> No. Few things are always true. :) However, see below.
>
>> My understanding was although A thinks the migration happens
>> instantaneously, it is in fact more likely to be pause+migrate+resume
>> and during that time anyone trying to talk to A during that time is
>> going to be disappointed.
>
> I tend to be with Vladislav on this one. The thing that most people
> would expect from a "live migration" is that it's interruption free.
> And what allow-migrate was first implemented for (iirc), live
> migrations for Xen, does fulfill that expectation. Same thing is true
> for live migrations in libvirt/KVM, and I think anyone would expect
> essentially the same thing from checkpoint/restore migrations where
> they're available.
>
> So I guess it's reasonable to assume that if one resource migrates,
> dependent resources need not be restarted.

Ok, could someone file a bug requesting the new behaviour please?

> But since Pacemaker now
> does restart them, you might need to figure out a way to preserve the
> existing functionality for users who rely on that. Not sure if any do,
> though.
>
> Cheers,
> Florian
>
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