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Hi Ryan,

Yes it is a little bit weird,  I think the reasons its doing this is likely due to it being the most generic solution to the resizing problem. I believe there is a flag like 'resize_same_host' but I haven't used it that might help.

I think your concern is valid though and could/should(?) be fixed.

You could imagine the scheduler 'preferring' the origin compute and the origin compute node in this case doing a 'fast path' resize path that would trigger the compute manager to just move some folders around (instead of invoking the ssh sequence you talked about). This would seem to make sense to me and would avoid the 'slow path' of actually moving the instance (and disks and so on) to a new node since the origin node doesn't have enough space/cpu/memory… That would make sense to me and likely with beefy enough compute nodes the 'fast path' would be the common case.

-Josh

From: Ryan Lane <rlane at wikimedia.org<mailto:rlane at wikimedia.org>>
Date: Tuesday, May 21, 2013 2:25 PM
To: Juan José Pavlik Salles <jjpavlik at gmail.com<mailto:jjpavlik at gmail.com>>
Cc: "openstack-operators at lists.openstack.org<mailto:openstack-operators at lists.openstack.org>" <openstack-operators at lists.openstack.org<mailto:openstack-operators at lists.openstack.org>>
Subject: Re: [Openstack-operators] resizing an instance

On Tue, May 21, 2013 at 2:20 PM, Juan José Pavlik Salles <jjpavlik at gmail.com<mailto:jjpavlik at gmail.com>> wrote:
I'm not sure about your deployment, but i noticed that when i try to resize a vm nova also tries to move the vm to another compute-node, so if you don't have a shared storage for the VMs this is not possible (unless your compute-node can ssh to the other compute-node ofcourse). I found in my logs thigs like "ssh root at node2 mkdir -p /var/lib/nova/instances/instances_dir" when trying to resize a VM. Tomorrow i'll trying resizing with shared storage and i'll let you know.


Yes. This is the weirdest behavior. Why in the world is it necessary to move the instance to another compute node just to do a resize? It requires ssh between instances, makes the process *much* slower and also makes it way more error prone. I don't get it. This seems like a really convoluted way of handling resizes.

Is there some really great reasoning behind this?

- Ryan
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