[openstack-dev] [nova] Placement API WSGI code -- let's just use flask

Sean Dague sean at dague.net
Tue Jun 21 12:00:50 UTC 2016

On 06/21/2016 07:39 AM, Jay Pipes wrote:
> On 06/21/2016 05:43 AM, Sylvain Bauza wrote:
>> Le 21/06/2016 10:04, Chris Dent a écrit :
>>> On Mon, 20 Jun 2016, Jay Pipes wrote:
>>>> Flask seems to be the most widely used and known WSGI framework so
>>>> for consistency's sake, I'm recommending we just use it and not rock
>>>> this boat. There are more important things to get hung up on than
>>>> this battle right now.
>>> That seems perfectly reasonable. My main goal in starting the
>>> discussion was to ensure that we reach some kind of consensus,
>>> whatever it might be[1]. It won't be too much of an ordeal to
>>> turn the existing pure WSGI stuff into Flask stuff.
>>> From my standpoint doing the initial development in straight WSGI
>>> was a win as it allowed for a lot of clarity from the inside out.
>>> Now that that development has shown the shape of the API we can
>>> do what we need to do to make it clear from outside in.
>>> Next question: There's some support for not using Paste and
>>> paste.ini. Is anyone opposed to that?
>> Given Flask is not something we support yet in Nova, could we discuss on
>> that during either a Nova meeting, or maybe wait for the midcycle ?
> I really don't want to wait for the mid-cycle. Happy to discuss in the
> Nova meeting, but my preference is to have Chris just modify his patch
> series to use Flask now and review it.
>> To be honest, Chris and you were saying that you don't like Flask, and
>> I'm a bit agreeing with you. Why now it's a good possibility ?
> Because Doug persuaded me that the benefits of being consistent with
> what the community is using outweigh my (and Chris') personal misgivings
> about the particular framework.

Just to be clear....


Flask is used by 2 (relatively new) projects in OpenStack

If we look at the iaas base layer:

Keystone - custom WSGI with Routes / Paste
Glance - WSME + Routes / Paste
Cinder - custom WSGI with Routes / Paste
Neutron - pecan + Routes / Paste
Nova - custom WSGI with Routes / Paste

I honestly don't think raw WSGI is a bad choice here. People are going
to be pretty familiar with it in related projects at this level.

Using selector instead of Routes makes things different for unclear
gain. Sticking with Routes seems more prudent.

Doing Flask is fine, but do it because we think that's the way things
should be done, not because it's a common in our community, which it
clearly is not. The common pattern is custom WSGI + Routes / Paste (at
least at this layer in the stack).


Sean Dague

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