Volume-backed flavors

Registered by Matt Riedemann on 2017-10-13

This is a blueprint for the short-term option described in this Queens PTG recap email:

http://lists.openstack.org/pipermail/openstack-dev/2017-September/122238.html

Related discussion from the Boston forum too:

http://lists.openstack.org/pipermail/openstack-dev/2017-May/117012.html

This proposes a new microversion to allow setting a volume_backed flag on flavors which will tell nova to auto-generate a volume-backed instance as long as there are no user or image-defined BDMs in the same request, as those take precedence.

This should simplify booting from volume for users and allow operators to configure all of their flavors to use persistent storage for the root disk.

Related efforts:

- https://gist.github.com/mgagne/161bd7eaeb4c747fa1ae97c0bc43c093
- https://specs.openstack.org/openstack/nova-specs/specs/newton/approved/flavor-root-disk-none.html
- https://blueprints.launchpad.net/nova/+spec/create-bdm-from-flavor-extra-specs
- https://blueprints.launchpad.net/nova/+spec/nova-ephemeral-cinder

Issues:

There will be discoverability issues with this given it's a new flavor attribute in a microversion. For example, an admin creates all of their flavors with volume_backed=True so Nova is going to create a volume-backed instance for all instances. However, if the user is only listing and showing flavor details at v2.1 (or any lower microversion than the one that added the new attribute), then they might be surprised why they have a volume-backed instance, and they might even delete it while it's being created (at the same time as the server create) which will actually make the server create fail. Hopefully the name of the flavor will be sufficient to explain it is a volume-backed flavor even if the attribute (or soon to be description field) doesn't get exposed to the user on v2.1.

Blueprint information

Status:
Not started
Approver:
None
Priority:
Medium
Drafter:
Matt Riedemann
Direction:
Needs approval
Assignee:
Matt Riedemann
Definition:
Drafting
Series goal:
None
Implementation:
Unknown
Milestone target:
None

Related branches

Sprints

Whiteboard

Gerrit topic: https://review.openstack.org/#q,topic:bp/volume-backed-flavors,n,z

Addressed by: https://review.openstack.org/511965
    Spec for volume-backed flavors

Spec wasn't approved in time for the Queens spec freeze, so deferring to Rocky. -- mriedem 20171102

(?)

Work Items

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