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Steve,
The problem with the support of live-migrate would still exist even if we decide to manage only one cluster from a compute node, unless one is ok with only live-migrate functionality between clusters.  The main debate started with supporting the live-migrate between the ESX Hosts in the same cluster.

Thanks,
Divakar

-----Original Message-----
From: Steve Gordon [mailto:sgordon at redhat.com] 
Sent: Wednesday, April 09, 2014 8:38 PM
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [OpenStack-Dev][Nova][VMWare] Enable live migration with one nova compute
Importance: High

----- Original Message -----
> I'm not writing off vCenter or its capabilities. I am arguing that the 
> bar for modifying a fundamental design decision in Nova -- that of 
> being horizontally scalable by having a single nova-compute worker 
> responsible for managing a single provider of compute resources -- was 
> WAY too low, and that this decision should be revisited in the future 
> (and possibly as part of the vmware driver refactoring efforts 
> currently underway by the good folks at RH and VMWare).

+1, This is my main concern about having more than one ESX cluster under a single nova-compute agent as well. Currently it works, but it doesn't seem particularly advisable as on face value as such an architecture seems to break a number of the Nova design guidelines around high availability and fault tolerance. To me it seems like such an architecture effectively elevates nova-compute into being part of the control plane where it needs to have high availability (when discussing on IRC yesterday it seemed like this *may* be possible today but more testing is required to shake out any bugs).

Now may well be the right approach *is* to make some changes to these expectations about Nova, but I think it's disingenuous to suggest that what is being suggested here isn't a significant re-architecting to resolve issues resulting from earlier hacks that allowed this functionality to work in the first place. Should be an interesting summit session.

-Steve

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