How to use hosts with no storage disks

James Penick jpenick at
Fri Oct 15 18:18:02 UTC 2021

You are correct, I meant you would use Ironic to provision the compute
node, which Nova would then use to provision VMs.

On Fri, Oct 15, 2021 at 11:16 AM A Monster <amonster369 at> wrote:

> As far as I know, ironic aims to provision bare metal machines instead of
> virtual machines, in my case, what I want to accomplish is to boot the
> host's operating system through network, and then use either a remote disk
> in which the image service copies the vm's image to, and then boot from
> that image, or if it's possible, use the ram instead of a disk for that
> task, and that would allow me to use diskless computer nodes (hosts).
> On Fri, 15 Oct 2021 at 18:06, James Penick <jpenick at> wrote:
>> This is something we've talked about doing at Yahoo some day. There are
>> three separate problems to solve:
>> 1. Diskless booting the compute node off the network. Mechanically this
>> is possible via a number of approaches. You'd have a ramdisk with the
>> necessary components baked in, so once the ramdisk loaded you'd be in the
>> OS. I'm not sure if this can be fully accomplished via Ironic as yet. I'd
>> need to ask an Ironic expert to weigh in.
>> 2. Configuration of the compute node. Either a CI job which is aware of
>> the compute node coming up and pushing configuration via something like
>> Ansible, or perhaps using cloud-init with the necessary pieces loaded into
>> a config-drive image which is provided as a part of the boot process. If we
>> can have Ironic manage diskless booting systems then this would be a solved
>> problem with user data.
>> 3. VM storage could either be "local" via a large ramdisk partition
>> (assuming you have a sufficient quantity of ram in your compute nodes), an
>> NFS share which is mounted to the compute node, or volume backed instances.
>> We were investigating this earlier this year and got stuck on the third
>> problem. Local storage via ramdisk isn't really an option for us, since we
>> already pack our compute nodes with a lot of ram, and we need that memory
>> for the instances. NFS has issues with security, since we don't want one
>> giant volume exported to all compute nodes due to security concerns, and a
>> per-compute node export would need to be orchestrated. Volume backed
>> instances seemed ideal, however we ran into some issues there, which are
>> partially related to the block storage product we use. I'm hopeful we'll
>> get back to this next year, a class of instance flavors booted on diskless
>> compute nodes would allow us to offer even more cost-effective options for
>> our customers.
>> -James
>> On Fri, Oct 15, 2021 at 3:54 AM A Monster <amonster369 at> wrote:
>>> In Openstack, is it possible to create compute nodes with no hard
>>> drives and use PXE in order to boot the host's system and therefore launch
>>> instances with no local drive which is needed to boot the VM's image.
>>> If not, what's the minimum storage needed to be given to hosts in order
>>> to get a fully functional system.
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