[openstack-dev] [Ironic] Manual scheduling nodes in maintenance mode

Robert Collins robertc at robertcollins.net
Tue Mar 18 19:24:37 UTC 2014

On 15 March 2014 13:07, Devananda van der Veen <devananda.vdv at gmail.com> wrote:
> +1 to the idea.
> However, I think we should discuss whether the rescue interface is the
> appropriate path. It's initial intention was to tie into Nova's rescue
> interface, allowing a user whose instance is non-responsive to boot into a
> recovery mode and access the data stored within their instance. I think
> there are two different use-cases here:
> Case A: a user of Nova who somehow breaks their instance, and wants to boot
> into a "rescue" or "recovery" mode, preserving instance data. This is useful
> if, eg, they lost network access or broke their grub config.
> Case B: an operator of the baremetal cloud whose hardware may be
> malfunctioning, who wishes to hide that hardware from users of Case A while
> they diagnose and fix the underlying problem.
> As I see it, Nova's rescue API (and by extension, the same API in Ironic) is
> intended for A, but not for B.  TripleO's use case includes both of these,
> and may be conflating them.

I agree.

> I believe Case A is addressed by the planned driver.rescue interface. As for
> Case B, I think the solution is to use different tenants and move the node
> between them. This is a more complex problem -- Ironic does not model
> tenants, and AFAIK Nova doesn't reserve unallocated compute resources on a
> per-tenant basis.
> That said, I think we will need a way to indicate "this bare metal node
> belongs to that tenant", regardless of the rescue use case.

I'm not sure Ironic should be involved in scheduling (and giving a
node to a tenant is a scheduling problem).

If I may sketch an alternative - when a node is put into maintenance
mode, keep publishing it to the scheduler, but add an extra spec to it
that won't match any request automatically.

Then 'deploy X to a maintenance node machine' is simple nove boot with
a scheduler hint to explicitly choose that machine, and all the
regular machinery will take place.


Robert Collins <rbtcollins at hp.com>
Distinguished Technologist
HP Converged Cloud

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