Got it!

By quota, do you mean reserved_host_disk_mb in nova.conf? I could make the /var/lib/nova/instances RO but I am not sure how that would impact config drive that are created locally (since I dont have ceph)

Just to be clear on the behavior, this means that boot-from-image requests would fail?

Looking at nova.conf, I can disable the number of local-disks supported, but this doesn't act as a behavior change when the requests are made.

I assume, from what I now know, that there is no mechanism to default/transform a request to BFV.

# A negative number means unlimited. Setting max_local_block_devices
# to 0 means that any request that attempts to create a local disk
# will fail. This option is meant to limit the number of local discs
# (so root local disc that is the result of --image being used, and
# any other ephemeral and swap disks). 0 does not mean that images
# will be automatically converted to volumes and boot instances from
# volumes - it just means that all requests that attempt to create a
# local disk will fail.
#
# Possible values:
#
# * 0: Creating a local disk is not allowed.
# * Negative number: Allows unlimited number of local discs.
# * Positive number: Allows only these many number of local discs.
#                        (Default value is 3).
#  (integer value)
#max_local_block_devices = 3

On Sun, Apr 3, 2022 at 5:54 AM Radosław Piliszek <radoslaw.piliszek@gmail.com> wrote:
On Sun, 3 Apr 2022 at 11:47, Radosław Piliszek
<radoslaw.piliszek@gmail.com> wrote:
>
> On Sat, 2 Apr 2022 at 16:00, Laurent Dumont <laurentfdumont@gmail.com> wrote:
> >
> > Hey folks,
>
> Hi Laurent,
>
> > I am trying to see if there are any ways to instruct Openstack to prevent the usage of local storage/ephemeral disks.
> >
> > There are cases where :
> >
> > I don't want the added complexity of Ceph.
> > I don't want the added hassle of using local volumes/nfs/shared storage on the computes directly.
> >
> > In an ideal world, creating a VM would mean that you always have a boot-from-volume with the volume being in your chosen backend.
> >
> > I've seen this spec : https://blueprints.launchpad.net/nova/+spec/flavor-root-disk-none
> >
> > But it doesn't seem to have survived the Ocata cycle.
> >
> > Any thoughts?
>
> You can set the root and ephemeral disk sizes to 0 which means the
> flavor is not usable without a volume.

Sorry, I somehow forgot to write the actual workaround.
There should be this sentence in here:
And then, make the nova's local disk store readonly / with a small quota.

> This way you are forced to use Cinder and what it offers.
>
> -yoctozepto