nova/releasenotes/notes/bug-1739646-enforce_volume_...

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---
security:
- |
A new policy rule, ``os_compute_api:servers:create:zero_disk_flavor``, has
been introduced which defaults to ``rule:admin_or_owner`` for backward
compatibility, but can be configured to make the compute
API enforce that server create requests using a flavor with zero root disk
must be volume-backed or fail with a ``403 HTTPForbidden`` error.
Allowing image-backed servers with a zero root disk flavor can be
potentially hazardous if users are allowed to upload their own images,
since an instance created with a zero root disk flavor gets its size
from the image, which can be unexpectedly large and exhaust local disk
on the compute host. See https://bugs.launchpad.net/nova/+bug/1739646 for
more details.
While this is introduced in a backward-compatible way, the default will
be changed to ``rule:admin_api`` in a subsequent release. It is advised
that you communicate this change to your users before turning on
enforcement since it will result in a compute API behavior change.