On 12/11/2013 11:47 PM, Mike Perez wrote:
On 10:06 Thu 12 Dec , Christopher Yeoh wrote:
On Thu, Dec 12, 2013 at 8:59 AM, Doug Hellmann
<doug.hellm...@dreamhost.com
<mailto:doug.hellm...@dreamhost.com>>wrote:
On Wed, Dec 11, 2013 at 3:41 PM, Ryan Petrello <
ryan.petre...@dreamhost.com
<mailto:ryan.petre...@dreamhost.com>>
wrote:
Hello,
I’ve spent the past week experimenting with using Pecan for
Nova’s
API,
and have opened an experimental review:
https://review.openstack.org/#/c/61303/6
…which implements the `versions` v3 endpoint using pecan (and
paves the
way for other extensions to use pecan). This is a *potential*
approach
I've considered for gradually moving the V3 API, but I’m open
to other suggestions (and feedback on this approach). I’ve
also got a few open questions/general observations:
1. It looks like the Nova v3 API is composed *entirely* of
extensions (including “core” API calls), and that extensions
and their routes are discoverable and extensible via installed
software that registers
itself
via stevedore. This seems to lead to an API that’s composed of
installed
software, which in my opinion, makes it fairly hard to map out
the
API (as
opposed to how routes are manually defined in other WSGI
frameworks). I
assume at this time, this design decision has already been
solidified for
v3?
Yeah, I brought this up at the summit. I am still having some
trouble understanding how we are going to express a stable core
API for compatibility testing if the behavior of the API can be
varied so significantly by deployment decisions. Will we just
list each
"required"
extension, and forbid any extras for a compliant cloud?
Maybe the issue is caused by me misunderstanding the term
"extension," which (to me) implies an optional component but is
perhaps reflecting a technical implementation detail instead?
Yes and no :-) As Ryan mentions, all API code is a plugin in the V3
API. However, some must be loaded or the V3 API refuses to start
up. In nova/api/openstack/__init__.py we have
API_V3_CORE_EXTENSIONS which hard codes which extensions must be
loaded and there is no config option to override this (blacklisting
a core plugin will result in the V3 API not starting up).
So for compatibility testing I think what will probably happen is
that we'll be defining a minimum set (API_V3_CORE_EXTENSIONS) that
must be implemented and clients can rely on that always being
present
on a compliant cloud. But clients can also then query through
/extensions what other functionality (which is backwards compatible
with respect to core) may also be present on that specific cloud.
This really seems similar to the idea of having a router class, some
controllers and you map them. From my observation at the summit,
calling everything an extension creates confusion. An extension
"extends" something. For example, Chrome has extensions, and they
extend the idea of the core features of a browser. If you want to do
more than back/forward, go to an address, stop, etc, that's an
extension. If you want it to play an audio clip "stop, hammer time"
after clicking the stop button, that's an example of an extension.
In OpenStack, we use extensions to extend core. Core are the
essential feature(s) of the project. In Cinder for example, core is
volume. In core you can create a volume, delete a volume, attach a
volume, detach a volume, etc. If you want to go beyond that, that's
an extension. If you want to do volume encryption, that's an example
of an extension.
I'm worried by the discrepancies this will create among the programs.
You mentioned maintainability being a plus for this. I don't think
it'll be great from the deployers perspective when you have one
program that thinks everything is an extension and some of them have
to be enabled that the deployer has to be mindful of, while the rest
of the programs consider all extensions to be optional.
+1. I agree with most of what Mike says above. The idea that there are
core "extensions" in Nova's v3 API doesn't make a whole lot of sense to me.
Best,
-jay
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