[openstack-dev] [devstack][neutron] Eliminating the DevStack layer

Assaf Muller assaf at redhat.com
Fri Apr 8 17:16:28 UTC 2016

On Fri, Apr 8, 2016 at 11:57 AM, Sean M. Collins <sean at coreitpro.com> wrote:
> Edgar Magana wrote:
>> This is a very solid plan. Maybe to fair on the current state of the devstack with neutron functionality, what will be the disadvantage(s) of this change from your perspective?
> A user's local.conf will probably get a little bigger - and I think a
> lot of the issues about Neutron's inability to run out of the box will
> be exposed.
> I mean let's face it - Neutron, installed from source, with no
> configuration Does Not Work™. There are not enough settings that have
> defaults set, for it to actually run.
> This was made painfully obvious to me when I had to make new revisions
> to the Neutron DevStack refactor, where I had to add more inisets, in
> order for Neutron to finish stacking correctly.
> Did you know, for example, that we rely on DevStack[1] to set the list
> of mechanism_drivers? Without this, you'll get an empty mechanism_driver
> list and nothing will ever be wired up.

I don't want to detract from what you're saying Sean, and I largely
agree that we can be more opinionated in Neutron and rely less on
Devstack. I also never liked Devstack's "macros" and have always
preferred configuring everything myself via local.conf when that was
made an option, simply because I already know how to configure Neutron
and I didn't want to learn Devstack's options. I do want to say that
ML2's "mechanism_drivers" option probably does not have a default for
the same reason we do not have a default for the core_plugin value, we
don't want to play favorites. From Neutron's point of view, ignoring
the existence of Devstack and upstream CI, I think that makes sense.

> I'm sure there is an argument that can be made about why there is no
> default for mechanism_drivers in ML2, since there are lots of options.
> But, I think that we can at least enable the ones that we have in
> Neutron's main tree. Packagers who make packages for each mechanism
> driver (LB, OVS, etc..) already had to handle things like
> mechanism_drivers in the Ml2 configuration already, so it shouldn't
> really impact them since we're only setting a default if nothing is set,
> and their packages should explicitly set it.
> [1]: https://github.com/openstack-dev/devstack/blob/master/lib/neutron_plugins/ml2#L27
> --
> Sean M. Collins
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