EmilienM
commented
3 months ago Awesome inputs @stephenfin , thanks for looking at it.
I see two things here:
- When providing additional block devices, we should get the total size of them and make sure the
OpenStackMachineflavour can support that size inOS-FLV-EXT-DATA:ephemeral. Send an error before creating the Machine. - When not providing additional block devices, we should validate that the flavor doesn't have a > 0 size value in
OS-FLV-EXT-DATA:ephemeral. Maybe send a warning and not an error? since it won't cause reconciliation issue.
stephenfin
k8s-triage-robot
/kind feature
Describe the solution you'd like
(Heads up: this is speculative based on code inspection. I have not yet attempted to reproduce the scenarios described here to prove things work the way I've said. I will though...unless someone beats me to it)
additionalBlockDevicesis expected to represent all non-root block devices attached to the instance. As of #1692, we are able to indicate the type of block device by setting thetypeproperty of the given block device, which allows us to create Nova-provisioned (a.k.a. "ephemeral") disk as well as the Cinder-provisioned disks previously supported. However, there are two nuances with Nova-provisioned disks that I don't think are accounted for. Firstly, while you can create multiple Nova-provisioned disks, the total capacity of those disks cannot exceed the GB value given in theOS-FLV-EXT-DATA:ephemeralproperty of the flavour. This will presumably cause non-obvious reconciler issue if a user tries to create e.g. twolocaltype BDMs of 10GB but the flavor hasOS-FLV-EXT-DATA:ephemeral = 15. Secondly, if no block device mapping is given but your flavor specifies a non-zero property forOS-FLV-EXT-DATA:ephemeral, you will still get a single volume corresponding to that property. This won't cause any reconciliation issues, but will lead to a situation where k8s' view of the server resource diverges from OpenStack's, which sounds like a Bad Thing :tm:Anything else you would like to add:
I recently wrote a blog about block devices in OpenStack to jot down my own understanding of BDMs in OpenStack. It may or may not be helpful. In any case, it can be found here https://that.guru/blog/block-devices-in-openstack/. Nova's own docs on the matter are spread out but the most important pieces (IMO) can be found here and here.