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Jay,
That sound reasonable.
We will need to document in a guide for driver developers what to do when new option is added deprecated in conf file for a driver.
Expect that nothing extra will need to be done beyond what we are doing now when new functionality added/deprecated from scheduler/default driver and perculates into drivers a release later.

I can also comment directly on the patch if it make sense.
Thanks,
Arkady

-----Original Message-----
From: Jay S. Bryant [mailto:jsbryant at electronicjungle.net]
Sent: Friday, March 20, 2015 5:02 PM
To: OpenStack Development Mailing List (not for usage questions)
Subject: [openstack-dev] [oslo][cinder][nova][neutron] going forward to oslo-config-generator ...

All,

Let me start with the TLDR;

Cinder, Nova and Neutron have lots of configuration options that need to be processed by oslo-config-generator to create the .conf.sample file. There are a couple of different ways this could be done. I have one proposal out, which has raised concerns, there is a second approach that could be taken which I am proposing below. Please read on if you have a strong opinion on the precedent we will try to set in Cinder. :-)

We discussed in the oslo meeting a couple of weeks ago a plan for how Cinder was going to blaze a trail to the new oslo-config-generator. The result of that discussion and work is here: [1] It needs some more work but has the bare bones pieces there to move to using oslo-config-generator.

With the change I have written extensive hacking checks that ensure that any lists that are registered with register_opts() are included in the base cinder/opts.py file that is then a single entry point that pulls all of the options together to generate the cinder.conf.sample file.
This has raised concern, however, that whenever a developer adds a new list of configuration options, they are going to have to know to go back to cinder/opts.py and add their module and option list there. The hacking check should catch this before code is submitted, but we are possibly setting ourselves up for cases where the patch will fail in the gate because updates are not made in all the correct places and because
pep8 isn't run before the patch is pushed.

It is important to note, that this will not happen every time a configuration option is changed or added, as was the case with the old check-uptodate.sh script. Only when a new list of configuration options is added which is a much less likely occurrence. To avoid this happening at all it was proposed by the Cinder team that we use the code I wrote for the hacking checks to dynamically go through the files and create cinder/opts.py whenever 'tox -egenconfig' is run. Doing this makes me uncomfortable as it is not consistent with anything else I am familiar with in OpenStack and is not consistent with what other projects are doing to handle this problem. In discussion with Doug Hellman, the approach also seemed to cause him concern. So, I don't believe that is the right solution.

An alternative that may be a better solution was proposed by Doug:

We could even further reduce the occurrence of such issues by moving the
list_opts() function down into each driver and have an entry point for oslo.config.opts in setup.cfg for each of the drivers. As with the currently proposed solution, the developer doesn't have to edit a top level file for a new configuration option. This solution adds that the developer doesn't have to edit a top level file to add a new configuration item list to their driver. With this approach the change would happen in the driver's list_opts() function, rather than in cinder/opts.py . The only time that setup.cfg would needed to edited is when a new package is added or when a new driver is added. This would reduce some of the already minimal burden on the developer. We, however, would need to agree upon some method for aggregating together the options lists on a per package (i.e. cinder.scheduler, cinder.api) level. This approach, however, also has the advantage of providing a better indication in the sample config file of where the options are coming from. That is an improvement over what I have currently proposed.

Does Doug's proposal sound more agreeable to everyone? It is important to note that the fact that some manual intervention is required to 'plumb' in the new configuration options was done by design. There is a little more work required to make options available to oslo-config-generator but the ability to use different namespaces, different sample configs, etc were added with the new generator. These additional capabilities were requested by other projects. So, moving to this design does have the potential for more long-term gain.

Thanks for taking the time to consider this!

Jay

[1] https://review.openstack.org/#/c/165431/


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