[Openstack-operators] How to handle updates of public images?

Kris G. Lindgren klindgren at godaddy.com
Thu Feb 5 19:16:19 UTC 2015

In the case of a raw backed qcow2 image (pretty sure that¹s the default)
the instances root disk as seen inside the vm is made up of changes made
on the instance disk (qcow2 layer) + the base image (raw).  Also, remember
that as currently coded a resize migration will almost always be a
migrate.  However, since the vm is successfully running on the old compute
node it *should* be a trivial change that if the backing image is no
longer available via glance - copy that over to the new host as well.
Kris Lindgren
Senior Linux Systems Engineer
GoDaddy, LLC.

On 2/5/15, 11:55 AM, "Clint Byrum" <clint at fewbar.com> wrote:

>Excerpts from George Shuklin's message of 2015-02-05 05:09:51 -0800:
>> Hello everyone.
>> We are updating our public images regularly (to provide them to
>> customers in up-to-date state). But there is a problem: If some
>> starts from image it becomes 'used'. That means:
>> * That image is used as _base for nova
>> * If instance is reverted this image is used to recreate instance's disk
>> * If instance is rescued this image is used as rescue base
>> * It is redownloaded during resize/migration (on a new compute node)
>Some thoughts:
>* All of the operations described should be operating on an image ID. So
>the other suggestions of renaming seems the right way to go. "Ubuntu
>14.04" becomes "Ubuntu 14.04 02052015" and the ID remains in the system
>for a while. If something inside Nova doesn't work with IDs, it seems
>like a bug.
>* rebuild, revert, rescue, and resize, are all very _not_ cloud things
>that increase the complexity of Nova. Perhaps we should all reconsider
>their usefulness and encourage our users to spin up new resources, use
>volumes and/or backup/restore methods, and then tear down old instances.
>One way to encourage them is to make it clear that these operations will
>only work for X amount of time before old versions images will be removed.
>So if you spin up Ubuntu 14.04 today, reverts and resizes and rescues
>are only guaranteed to work for 6 months. Then aggressively clean up >
>6 month old image ids. To make this practical, you might even require
>a role, something like "reverter", "rescuer", "resizer" and only allow
>those roles to do these operations, and then before purging images,
>notify those users in those roles of instances they won't be able to
>resize/rescue/revert anymore.
>It also makes no sense to me why migrating an instance requires its
>original image. The instance root disk is all that should matter.
>OpenStack-operators mailing list
>OpenStack-operators at lists.openstack.org

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