Open Stack

On 03/17/2015 02:33 PM, Joe Gordon wrote:

> Digging up this old thread because I am working on getting multi node live
> migration testing working (https://review.openstack.org/#/c/165182/), and just
> ran into this issue (bug 1398999).
>
> And I am not sure I agree with this statement. I think there is a valid case for
> doing block migrate with a cinder volume attached to an instance:
>
>
> * Cloud isn't using a shared filesystem for ephemeral storage
> * Instance is booted from an image, and a volume is attached afterwards. An
> admin wants to take the box the instance is running on offline for maintanince
> with a minimal impact to the instances running on it.
>
> What is the recommended solution for that use case? If the admin disconnects and
> reconnects the volume themselves is there a risk of impacting whats running on
> the instance? etc.

Interesting bug.  I think I agree with you that there isn't a good solution 
currently for instances that have a mix of shared and not-shared storage.

I'm curious what Daniel meant by saying that marking the disk shareable is not 
as reliable as we would want.

I think there is definitely a risk if the admin disconnects the volume--whether 
or not that causes problems depends on whether the application can handle that 
cleanly.

I suspect the "proper" cloud-aware strategy would be to just kill it and have 
another instance take over.  But that's not very helpful for 
not-fully-cloud-aware applications.

Also, since you've been playing in this area...do you know if we currently 
properly support all variations on live/cold migration, resize, evacuate, etc. 
for the boot-from-volume case?

Chris