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Excerpts from Thomas Spatzier's message of 2013-11-19 23:35:40 -0800:
> Excerpts from Steve Baker's message on 19.11.2013 21:40:54:
> > From: Steve Baker <sbaker at redhat.com>
> > To: openstack-dev at lists.openstack.org,
> > Date: 19.11.2013 21:43
> > Subject: Re: [openstack-dev] [Heat] HOT software configuration
> > refined after design summit discussions
> >
> <snip>
> > I think there needs to a CM tool specific agent delivered to the server
> > which os-collect-config invokes. This agent will transform the config
> > data (input values, CM script, CM specific specialness) to a CM tool
> > invocation.
> >
> > How to define and deliver this agent is the challenge. Some options are:
> > 1) install it as part of the image customization/bootstrapping (golden
> > images or cloud-init)
> > 2) define a (mustache?) template in the SoftwareConfig which
> > os-collect-config transforms into the agent script, which
> > os-collect-config then executes
> > 3) a CM tool specific implementation of SoftwareApplier builds and
> > delivers a complete agent to os-collect-config which executes it
> >
> > I may be leaning towards 3) at the moment. Hopefully any agent can be
> > generated with a sufficiently sophisticated base SoftwareApplier type,
> > plus maybe some richer intrinsic functions.
> 
> This is good summary of options; about the same we had in mind. And we were
> also leaning towards 3. Probably the approach we would take is to get a
> SoftwareApplier running for one CM tool (e.g. Chef), then look at another
> tool (base shell scripts), and then see what the generic parts art that can
> be factored into a base class.
> 
> > >> The POC I'm working on is actually backed by a REST API which does
> dumb
> > >> (but structured) storage of SoftwareConfig and SoftwareApplier
> entities.
> > >> This has some interesting implications for managing SoftwareConfig
> > >> resources outside the context of the stack which uses them, but lets
> not
> > >> worry too much about that *yet*.
> > > Sounds good. We are also defining some blueprints to break down the
> overall
> > > software config topic. We plan to share them later this week, and then
> we
> > > can consolidate with your plans and see how we can best join forces.
> > >
> > >
> > At this point it would be very helpful to spec out how specific CM tools
> > are invoked with given inputs, script, and CM tool specific options.
> 
> That's our plan; and we would probably start with scripts and chef.
> 
> >
> > Maybe if you start with shell scripts, cfn-init and chef then we can all
> > contribute other CM tools like os-config-applier, puppet, ansible,
> > saltstack.
> >
> > Hopefully by then my POC will at least be able to create resources, if
> > not deliver some data to servers.
> 
> We've been thinking about getting metadata to the in-instance parts on the
> server and whether the resources you are building can serve the purpose.
> I.e. pass and endpoint to the SoftwareConfig resources to the instance and
> let the instance query the metadata from the resource. Sounds like this is
> what you had in mind, so that would be a good point for integrating the
> work. In the meantime, we can think of some shortcuts.
> 

Note that os-collect-config is intended to be a light-weight generic
in-instance agent to do exactly this. Watch for Metadata changes, and
feed them to an underlying tool in a predictable interface. I'd hope
that any of the appliers would mostly just configure os-collect-config
to run a wrapper that speaks os-collect-config's interface.

The interface is defined in the README:

https://pypi.python.org/pypi/os-collect-config

It is inevitable that we will extend os-collect-config to be able to
collect config data from whatever API these config applier resources
make available. I would suggest then that we not all go off and reinvent
os-collect-config for each applier, but rather enhance os-collect-config
as needed and write wrappers for the other config tools which implement
its interface.

os-apply-config already understands this interface for obvious reasons.

Bash scripts can use os-apply-config to extract individual values, as
you might see in some of the os-refresh-config scripts that are run as
part of tripleo. I don't think anything further is really needed there.

For chef, some kind of ohai plugin to read os-collect-config's collected
data would make sense.