Open Stack

On 06/08/14 13:30, Robert Collins wrote:
> On 6 August 2014 17:27, Tom Fifield <tom at openstack.org> wrote:
>> On 06/08/14 13:24, Robert Collins wrote:
>
>>> What happened to your DB migrations then? :)
>>
>>
>> Sorry if I misunderstood, I thought we were talking about running VM
>> downtime here?
>
> While DB migrations are running things like the nova metadata service
> can/will misbehave - and user code within instances will be affected.
> Thats arguably VM downtime.
>
> OTOH you could define it more narrowly as 'VMs are not powered off' or
> 'VMs are not stalled for more than 2s without a time slice' etc etc -
> my sense is that most users are going to be particularly concerned
> about things for which they have to *do something* - e.g. VMs being
> powered off or rebooted - but having no network for a short period
> while vifs are replugged and the overlay network re-establishes itself
> would be much less concerning.

I think you've got it there, Rob - nicely put :)

In many cases the users I've spoken to who are looking for a live path 
out of nova-network on to neutron are actually completely OK with some 
"API service" downtime (metadata service is an API service by their 
definition). A little 'glitch' in the network is also OK for many of them.

Contrast that with the original proposal in this thread ("snapshot VMs 
in old nova-network deployment, store in Swift or something, then launch 
VM from a snapshot in new Neutron deployment") - it is completely 
unacceptable and is not considered a migration path for these users.


Regards,


Tom