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On 10/16/2014 09:00 AM, Florian Haas wrote:
> On Thu, Oct 16, 2014 at 1:59 PM, Russell Bryant <rbryant at redhat.com> wrote:
>> On 10/16/2014 04:29 AM, Florian Haas wrote:
>>>>>>> (5) Let monitoring and orchestration services deal with these use
>>>>>>> cases and
>>>>>>> have Nova simply provide the primitive API calls that it already does
>>>>>>> (i.e.
>>>>>>> host evacuate).
>>>>>>
>>>>>> That would arguably lead to an incredible amount of wheel reinvention
>>>>>> for node failure detection, service failure detection, etc. etc.
>>>>>
>>>>> How so? (5) would use existing wheels for monitoring and orchestration
>>>>> instead of writing all new code paths inside Nova to do the same thing.
>>>>
>>>> Right, there may be some confusion here ... I thought you were both
>>>> agreeing that the use of an external toolset was a good approach for the
>>>> problem, but Florian's last message makes that not so clear ...
>>>
>>> While one of us (Jay or me) speaking for the other and saying we agree
>>> is a distributed consensus problem that dwarfs the complexity of
>>> Paxos, *I* for my part do think that an "external" toolset (i.e. one
>>> that lives outside the Nova codebase) is the better approach versus
>>> duplicating the functionality of said toolset in Nova.
>>>
>>> I just believe that the toolset that should be used here is
>>> Corosync/Pacemaker and not Ceilometer/Heat. And I believe the former
>>> approach leads to *much* fewer necessary code changes *in* Nova than
>>> the latter.
>>
>> Have you tried pacemaker_remote yet?  It seems like a better choice for
>> this particular case, as opposed to using corosync, due to the potential
>> number of compute nodes.
> 
> I'll assume that you are *not* referring to running Corosync/Pacemaker
> on the compute nodes plus pacemaker_remote in the VMs, because doing
> so would blow up the separation between the cloud operator and tenant
> space.

Correct.

> Running compute nodes as baremetal extensions of a different
> Corosync/Pacemaker cluster (presumably the one that manages the other
> Nova services)  would potentially be an option, although vendors would
> need to buy into this. Ubuntu, for example, currently only ships
> pacemaker-remote in universe.

Yes, this is what I had in mind.

-- 
Russell Bryant