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Re: Twisted or Eventlet?


If we are going to go through a major rewrite, I would suggest that we spend
some serious time improving our test coverage, especially
integration/smoketests. We need to know when our changes are breaking
things.  Any manpower that we can devote to this now will dramatically
decrease the pain of switching over components in the future.  I think
switching one component at a time is probably the right way to go as well.


On Wed, Aug 4, 2010 at 9:03 AM, Michael Gundlach <
michael.gundlach@xxxxxxxxxxxxx> wrote:

> All,
> I propose that we go ahead and decide to use Eventlet.  We've all had a
> chance to talk, the decision isn't going to make itself, and it seems like
> we're coalescing around Eventlet:
>    - In a long discussion about how to keep our code loosely coupled and
>    easy to maintain (see Architecture For Shared Components on the openstack
>    list), we concluded that WSGI would be a great solution, and eday has
>    prototyped an Eventlet-powered WSGI app talking AMQP to Rabbit.  The Twisted
>    WSGI approach apparently isn't stable or standard, but WSGI works just as
>    you'd expect in Eventlet.
>    - As hazmat points out in the "twisted v. eventlet" thread, you can't
>    use pdb with Twisted, while pdb works just as you'd hope in Eventlet.
>    - hazmat's experience during his lightning talk (see the same thread)
>    is a good datapoint verifying that people unfamiliar with either project
>    will probably prefer to work with Eventlet over Twisted: good for
>    recruiting.
>    - It's a weaker argument, but it's really hard to find any comparisons
>    between Twisted and Eventlet on the web that say Twisted is preferable (has
>    anyone found any?)
> And as always, there's the argument that Eventlet code is easier to read
> and understand, and therefore to maintain.
> I'm going to be working on adding the RS API to Nova, and I'm going to
> proceed in Eventlet.  If anyone feels strongly that we must use Twisted
> instead, speak up; otherwise, shall we call this decision made?
> trying-to-build-consensus-ly yrs,
> Michael
> On Tue, Aug 3, 2010 at 8:13 AM, Soren Hansen <soren.hansen@xxxxxxxxxxxxx>wrote:
>> On Mon, Aug 02, 2010 at 05:21:23PM -0500, Eric Day wrote:
>> > I took a closer look at the inner workings of how Twisted is currently
>> > being used, and I think there is still a good chunk of work to be done
>> > to make things work properly. For example, both Redis and AMQP modules
>> > are not using the Twisted I/O event loop. Both are still issuing sync
>> > socket calls in their own libs which could block the entire
>> > application.
>> Yup, this definitely needs fixing.
>> > These things are very doable in Twisted, it will just require using
>> > the txRedis and txAMQP modules. It will also introduce more deferreds
>> > into the mix since we'll have non-blocking connections dependent on
>> > each other. From this perspective, Eventlet may be easier since we
>> > could still use the current libraries by patching
>> > (http://eventlet.net/doc/patching.html).
>> Yes, both python-redis and python-amqplib use Python's standard socket
>> module, so they can be patched.
>> Does anyone know how eventlet would deal with libvirt calls?
>> python-libvirt just calls into libvirt obviously doesn't use Python's
>> socket module.
>> --
>> Soren Hansen
>> Systems Architect
>> The Rackspace Cloud
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