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Hi Tony,

Have you considered doing a “Tech Refresh” process? The companies I’ve worked at consider VMs ephemeral. When we need to replace a cluster, we build the new one, notify the users to create new VMs there, and then delete the old ones and take down the old cluster. We give them tools like Forklift to help migrate, but we make it their responsibility to create the new VM and move their data over.

From: Tony Pearce <tony.pearce at cinglevue.com>
Sent: Thursday, January 30, 2020 1:58 AM
To: Tobias Urdin <tobias.urdin at binero.se>
Cc: OpenStack Discuss ML <openstack-discuss at lists.openstack.org>
Subject: Re: [cinder][nova] Migrating servers' root block devices from a cinder backend to another

Thanks Tobias - thats my last resort. I'd still need to upload that image to the new openstack and then build an instance from the image. I'd also need to use metadata to make sure the instance was built with the same components (IP address etc).



Tony Pearce   |  Senior Network Engineer / Infrastructure Lead
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On Thu, 30 Jan 2020 at 17:55, Tobias Urdin <tobias.urdin at binero.se<mailto:tobias.urdin at binero.se>> wrote:
Another approach would be to export the data to Glance and download then you can upload it somewhere.

There is no ready thing that I know about. We used the openstacksdk to simply recreate the steps we did on CLI.
Create all the neccesary resources on the other side, create new instances from the migrated volume and set a fixedIP on the neutron port to get same IP address.
On 1/30/20 9:43 AM, Tony Pearce wrote:
I want to do something similar soon and don't want to touch the db (I experimented with cloning the "controller" and it did not achieve any desired outcome).

Is there a way to export an instance from Openstack in terms of something like a script that could re-create it on another openstack as a like-for-like? I guess this is assuming that the instance is linux-based and has cloud-init enabled.



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On Thu, 30 Jan 2020 at 16:39, Tobias Urdin <tobias.urdin at binero.se<mailto:tobias.urdin at binero.se>> wrote:
We did this something similar recently, we booted all instances from Cinder volume (with "Delete on terminate" set) in an old platform.

So we added our new Ceph storage to the old platform, removed instances (updated delete_on_terminate to 0 in Nova DB).
Then we issued a retype so cinder-volume performed a `dd` of the volume from the old to the new storage.

We then synced network/subnet/sg and started instances with same fixed IP and moved floating IPs to the new platform.

Since you only have to swap storage you should experiment with powering off the instances and try doing a migrate of the volume
but I suspect you need to either remove the instance or do some really nasty database operations.

I would suggest always going through the API and recreate the instance from the migrated volume instead of changing in the DB.
We had to update delete_on_terminate in DB but that was pretty trivial (and I even think there is a spec that is not implemented yet that will allow that from API).
On 1/29/20 9:54 PM, Jean-Philippe Méthot wrote:
Hi,

We have a several hundred VMs which were built on cinder block devices as root drives which use a SAN backend. Now we want to change their backend from the SAN to Ceph.
We can shutdown the VMs but we will not destroy them. I am aware that there is a cinder migrate volume command to change a volume’s backend, but it requires that the volume be completely detached. Forcing a detached state on
that volume does let the volume migration take place, but the volume’s path in Nova block_device_mapping doesn’t update, for obvious reasons.

So, I am considering forcing the volumes to a detached status in Cinder and then manually updating the nova db block_device_mapping entry for each volume so that the VM can boot back up afterwards.
However, before I start toying with the database and accidentally break stuff, has anyone else ever done something similar? Got any tips or hints on how best to proceed?

Jean-Philippe Méthot
Openstack system administrator
Administrateur système Openstack
PlanetHoster inc.






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