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Thanks Jay and Chris for the comments!

@Jay Pipes, I think that we still need to enable "one nova compute live
migration" as one nova compute can manage multiple clusters and VMs can be
migrated between those clusters managed by one nova compute. For cell,
IMHO, each "cell" can be treated as a small "cloud" but not a "compute",
each "cell cloud" should be able to handle VM operations in the small cloud
itself. Please correct me if I am wrong.

@Chris, "OS-EXT-SRV-ATTR:host" is the host where nova compute is running
and "OS-EXT-SRV-ATTR:hypervisor_hostname" is the hypervisor host where the
VM is running. Live migration is now using "host" for live migration. What
I want to do is enable migration with one "host" and the "host" managing
multiple "hyperviosrs".

I'm planning to draft a bp for review which depend on
https://blueprints.launchpad.net/nova/+spec/vmware-auto-inventory

Thanks!


2014-04-04 8:03 GMT+08:00 Chris Friesen <chris.friesen at windriver.com>:

> On 04/03/2014 05:48 PM, Jay Pipes wrote:
>
>> On Mon, 2014-03-31 at 17:11 +0800, Jay Lau wrote:
>>
>>> Hi,
>>>
>>> Currently with VMWare VCDriver, one nova compute can manage multiple
>>> clusters/RPs, this caused cluster admin cannot do live migration
>>> between clusters/PRs if those clusters/PRs managed by one nova compute
>>> as the current live migration logic request at least two nova
>>> computes.
>>>
>>>
>>> A bug [1] was also filed to trace VMWare live migration issue.
>>>
>>> I'm now trying the following solution to see if it is acceptable for a
>>> fix, the fix wants enable live migration with one nova compute:
>>> 1) When live migration check if host are same, check both host and
>>> node for the VM instance.
>>> 2) When nova scheduler select destination for live migration, the live
>>> migration task should put (host, node) to attempted hosts.
>>> 3) Nova scheduler needs to be enhanced to support ignored_nodes.
>>> 4) nova compute need to be enhanced to check host and node when doing
>>> live migration.
>>>
>>
>> What precisely is the point of "live migrating" an instance to the exact
>> same host as it is already on? The failure domain is the host, so moving
>> the instance from one "cluster" to another, but on the same host is kind
>> of a silly use case IMO.
>>
>
> Here is where precise definitions of "compute node",
> "OS-EXT-SRV-ATTR:host", and "OS-EXT-SRV-ATTR:hypervisor_hostname", and
> "host" as understood by novaclient would be nice.
>
> Currently the "nova live-migration" command takes a "host" argument. It's
> not clear which of the above this corresponds to.
>
> My understanding is that one nova-compute process can manage multiple
> VMWare physical hosts.  So it could make sense to support live migration
> between separate VMWare hosts even if they're managed by a single
> nova-compute process.
>
> Chris
>
>
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-- 
Thanks,

Jay
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