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On Fri, Dec 23, 2016 at 02:21:00PM +0000, Steven Hardy wrote:
> I commented on the bug, I'm not sure about this as it seems to overlap with
> our service_config_settings interface, which IIRC landed slightly after
> your previous patches for opstools things, and potentially provides a
> cleaner way to approach this.

I'm not sure I see how to apply that, but let me further describe the
use case and you can perhaps point me in the right direction.

> Perhaps you can point to some examples of this usage, then we can compare
> with the service_config_settings approach?
> 
> I suspect the main difference is you need to append data for each service
> to e.g the collectd configuration?

Let's take the existing Fluentd support as an example.  We want the
ability for every service to provide a logging source configuation for
Fluentd, which will get aggregated into a logging_sources
list and then ultimately used in puppet-tripleo to populate a series
of ::fluentd::config resources.

Currently, the aggregation happens in a combination of
puppet/services/services.yaml (which aggregates the logging_source
attribute from all the services in the service chain) and in
overcloud.j2.yaml (which actually instantiates the hiera data).

With the LateServiceChain I've proposed, this could all be isolated
inside the fluentd composable service: it would not be necessary to
expose any of this logic in either services.yaml or overcloud.j2.yaml,
leading.  Additionally, it would not require the fluentd service to
have any a priori knowledge of what services were in use; it would
simply aggregate any configuration information that is provided in the
primary service chain.  It would also allow us to get rid of the
"LoggingConfiguration" resource, which only exists as a way to expose
certain parameter_defaults inside services.yaml.

-- 
Lars Kellogg-Stedman <lars at redhat.com> | larsks @ {freenode,twitter,github}
Cloud Engineering / OpenStack          | http://blog.oddbit.com/

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