On 6/6/2018 7:55 AM, Jay Pipes wrote:
I'd love to know who is actually using the swap_volume() functionality,
actually. I'd especially like to know who is using swap_volume() with
multiattach.
The swap volume API in nova only exists as a callback routine during
volume live migration or retype operations. It's admin-only by default
on the nova side, and shouldn't be called directly (similar to
guest-assisted volume snapshots for NFS and GlusterFS volumes - totally
just a callback from Cinder). So during volume retype, cinder will call
swap volume in nova and then nova will call another admin-only API in
Cinder to tell Cinder, yup we did it or we failed, rollback.
The cinder API reference on retype mentions the restrictions about
multiattach volumes:
https://developer.openstack.org/api-ref/block-storage/v3/#retype-a-volume
"Retyping an in-use volume from a multiattach-capable type to a
non-multiattach-capable type, or vice-versa, is not supported. It is
generally not recommended to retype an in-use multiattach volume if that
volume has more than one active read/write attachment."
There is no API reference for volume live migration, but it should
generally be the same idea.
The Tempest test for swap volume with multiattach volumes was written
before we realized we needed to put restrictions in place *on the cinder
side* to limit the behavior. The Tempest test just hits the compute API
to verify the plumbing in nova works properly, it doesn't initiate the
flow via an actual retype (or volume live migration).
--
Thanks,
Matt
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