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:


"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).




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