[openstack-dev] [Heat] HOT software configuration refined after design summit discussions

Clint Byrum clint at fewbar.com
Tue Nov 19 21:28:31 UTC 2013

Excerpts from Steve Baker's message of 2013-11-19 13:06:21 -0800:
> On 11/20/2013 09:50 AM, Clint Byrum wrote:
> > Excerpts from Steve Baker's message of 2013-11-18 12:52:04 -0800:
> >> Regarding apply_config/remove_config, if a SoftwareApplier resource is
> >> deleted it should trigger any remove_config and wait for the server to
> >> acknowledge when that is complete. This allows for any
> >> evacuation/deregistering workloads to be executed.
> >>
> > I'm a little worried about the road that leads us down. Most configuration
> > software defines forward progress only. Meaning, if you want something
> > not there, you don't remove it from your assertions, you assert that it
> > is not there.
> >
> > The reason this is different than the way we operate with resources is
> > that resources are all under Heat's direct control via well defined
> > APIs. In-instance things, however, will be indirectly controlled. So I
> > feel like focusing on a "diff" mechanism for user-deployed tools may be
> > unnecessary and might confuse. I'd much rather have a "converge"
> > mechanism for the users to focus on.
> >
> >
> A specific use-case I'm trying to address here is tripleo doing an
> update-replace on a nova compute node. The remove_config contains the
> workload to evacuate VMs and signal heat when the node is ready to be
> shut down. This is more involved than just "uninstall the things".
> Could you outline in some more detail how you think this could be done?

So for that we would not remove the software configuration for the
nova-compute, we would assert that the machine needs vms evacuated.
We want evacuation to be something we explicitly do, not a side effect
of deleting things. Perhaps having delete hooks for starting delete
work-flows is right, but it set off a red flag for me so I want to make
sure we think it through.

Also IIRC, evacuation is not necessarily an in-instance thing. It looks
more like the weird thing we've been talking about lately which is
"how do we orchestrate tenant API's":


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