How to use hosts with no storage disks

James Penick jpenick at
Fri Oct 15 17:06:21 UTC 2021

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.


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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