[openstack-dev] [packaging][neutron] --config-dir vs. --config-file

Ben Nemec openstack at nemebean.com
Fri Mar 13 18:53:36 UTC 2015

Hash: SHA1

On 03/13/2015 09:11 AM, Ihar Hrachyshka wrote:
> Hi all,
> (I'm starting a new [packaging] tag in this mailing list to reach
> out people who are packaging our software in distributions and
> whatnot.)
> Neutron vendor split [1] introduced situations where the set of 
> configuration files for L3/VPN agent is not stable and depends on 
> which packages are installed in the system. Specifically, 
> fwaas_driver.ini file is now shipped in neutron_fwaas tarball 
> (openstack-neutron-fwaas package in RDO), and so 
> --config-file=/etc/neutron/fwaas_driver.ini argument should be
> passed to L3/VPN agent *only* when the new package with the file is
> installed.
> In devstack, we solve the problem by dynamically generating CLI 
> arguments list based on which services are configured in
> local.conf [2]. It's not a viable approach in proper distribution
> packages though, where we usually hardcode arguments [3] in our
> service manifests (systemd unit files, in case of RDO).
> The immediate solution to solve the issue would be to use
> --config-dir argument that is also provided to us by oslo.config
> instead of --config-file, and put auxiliary files there [4] (those
> may be just symbolic links to actual files).
> I initially thought to put the directory under /etc/neutron/, but
> then realized we may be interested in keeping it out of user sight
> while it only references stock (upstream) configuration files.
> But then a question arises: whether it's useful just for this 
> particular case? Maybe there is value in using --config-dir outside
> of it? And in that case, maybe the approach should be replicated to
> other services?
> AFAIU --config-dir could actually be useful to configure services.
> Now instead of messing with configuration files that are shipped
> with packages (and handling .rpmnew files [5] that are generated on
> upgrade when local changes to those files are detected), users (or 
> deployment/installation tools) could instead drop a *.conf file in 
> that configuration directory, being sure their stock configuration 
> file is always current, and no .rpmnew files are there to manually 
> solve conflicts).
> We can also use two --config-dir arguments, one for stock/upstream 
> configuration files, located out of /etc/neutron/, and another one 
> available for population with user configuration files, under 
> /etc/neutron/. This is similar to how we put settings considered to
> be 'sane distro defaults' in neutron-dist.conf file that is not
> available for modification [6][7].
> Of course users would still be able to set up their deployment the
> old way. In that case, nothing will change for them. So the
> approach is backwards compatible.
> I wonder whether the idea seems reasonable and actually useful for 
> people. If so, we may want to come up with some packaging
> standards (on where to put those config-dir(s), how to name them,
> how to maintain symbolic links inside them) to avoid more work for
> deployment tools.

This is essentially what tripleo does as well, for similar reasons I
believe.  For example, nova-api is configured like this:

Maybe a little hard to parse if you're not familiar with
os-svc-daemon, but essentially it's starting nova-api with
"--config-dir /etc/nova --config-dir /etc/nova/api" so we can
configure nova-api without stepping on any other service, and still
have common configs in /etc/nova.

AFAIK it has worked well for us, and it does seem like a more flexible
way to handle configs so +1 to doing it elsewhere too.

- -Ben

> [1]: 
> https://blueprints.launchpad.net/neutron/+spec/core-vendor-decomposition
> http://git.openstack.org/cgit/openstack-dev/devstack/tree/lib/neutron#n393
> https://github.com/openstack-packages/neutron/blob/f20-master/neutron-l3-agent.service#L8
[4]: https://review.gerrithub.io/#/c/218562/
> [5]: 
> https://ask.fedoraproject.org/en/question/25722/what-are-rpmnew-files/
> https://github.com/openstack-packages/neutron/blob/f20-master/neutron-dist.conf
> https://github.com/openstack-packages/neutron/blob/f20-master/openstack-neutron.spec#L700
>  Regards, /Ihar
> /Ihar
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