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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