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On 8/27/2018 1:53 PM, Matt Riedemann wrote:
> On 8/27/2018 12:11 PM, Miguel Lavalle wrote:
>> Isn't multiple port binding what we need in the case of ports? In my 
>> mind, the big motivator for multiple port binding is the ability to 
>> change a port's backend
> 
> Hmm, yes maybe. Nova's usage of multiple port bindings today is 
> restricted to live migration which isn't what we're supporting with the 
> initial cross-cell (cold) migration support, but it could be a 
> dependency if that's what we need.
> 
> What I was wondering is if there is a concept like a port spanning or 
> migrating across networks? I'm assuming there isn't, and I'm not even 
> sure if that would be required here. But it would mean there is an 
> implicit requirement that for cross-cell migration to work, neutron 
> networks need to span cells (similarly storage backends would need to 
> span cells).

In thinking about this again (sleepless at 3am of course), port bindings 
doesn't help us here if we're orchestrating the cross-cell move using 
shelve offload, because in that case the port is unbound from the source 
host - while the instance is shelved offloaded, it has no host. When we 
unshelve in the new cell, we'd update the port binding. So there isn't 
really a use in this flow for multiple port bindings on multiple hosts 
(assuming we stick with using the shelve/unshelve idea here).

-- 

Thanks,

Matt