Hi All!
We have users who use 'rebuild' on volume booted servers before nova microversion 2.93, relying on the behavior that it keeps the volume as is. And they would like to keep doing this even after the openstack distro moves to a(n at least) zed base (sometime in the future).
As a naive user, it seems to me both behaviors make sense. I can easily imagine use cases for rebuild with and without reimaging. However since the implementation of https://specs.openstack.org/openstack/nova-specs/specs/zed/implemented/volum... rebuild without reimaging is only possible using an old microversion (<2.93). With that change merged, rebuild without reimaging seems to be a somewhat less than fully supported feature. A few examples of what I mean by that:
First, there's this warning: https://opendev.org/openstack/python-openstackclient/src/commit/5eb89e4ca1ce...
In which it is unclear to me what exactly will become an error in a future release. Rebuild with a different image? Or any rebuild with microversion <2.93?
Then old nova microversions may get dropped. Though what I heard from nova folks, this is unlikely to happen.
Then there are a few hypothetical situations like: a) Rebuild gets a new api feature (in a new microversion) which can never be combined with the do-not-reimage behavior. b) Rebuild may have a bug, whose fix requires a microversion bump. This again can never be combined with the old behavior.
What do you think, are these concerns purely theoretical or real? If we would like to keep having rebuild without reimaging, can we rely on the old microversion indefinitely? Alternatively shall we propose and implement a nova spec to explicitly expose the choice in the rebuild api (just to express the idea: osc server rebuild --reimage|--no-reimage)?
If the topic is worth further discussion beyond the ML, I can also bring it to the nova ptg.
Thanks in advance, Bence Romsics (rubasov)
ps: I'll be afk for a few days, but I'll follow up next Tuesday.