[openstack-dev] [all] re-introducing twisted to global-requirements

Doug Hellmann doug at doughellmann.com
Fri Jan 8 19:30:04 UTC 2016

Excerpts from Jim Rollenhagen's message of 2016-01-08 09:56:46 -0800:
> On Fri, Jan 08, 2016 at 11:00:35AM +0100, Thierry Carrez wrote:
> > Jim Rollenhagen wrote:
> > >[...]
> > >Here's the catch - mimic is built on twisted. I know twisted was
> > >previously removed from OpenStack (or at least people said "pls no", I
> > >don't know the full history). We didn't intend to stealth-introduce
> > >twisted back into g-r, but it was pointed out to me that it may appear
> > >this way, so here I am letting everyone know. lifeless pointed out that
> > >when tests are failing, people may end up digging into mimic or twisted
> > >code, which most people in this community aren't familiar with AFAIK,
> > >which is a valid point though I hope it isn't required often.
> > 
> > A bit of history with Twisted.
> > 
> > Back in 2010 we decided we could not afford asking OpenStack developers to
> > be familiar with multiple service architecture frameworks, and eventlet was
> > chosen as the simplest framework to learn and debug. The best reference I
> > found on this is still visible in the wiki:
> > 
> > https://wiki.openstack.org/wiki/UnifiedServiceArchitecture
> > 
> > >So, the primary question here is: do folks have a problem with adding
> > >twisted here? We're holding off on Ironic changes that depend on this
> > >until this discussion has happened, but aren't reverting the g-r change
> > >until we decide one way or another.
> > 
> > The only friction I see is how many developers would be expected to need to
> > learn Twisted in order to complete their jobs. My understanding is that
> > Twisted expertise could be needed to debug python-ironicclient functional
> > tests, which makes the cost relatively limited. So if Mimic brings in a
> > clear and significant benefit, I don't think its Twisted dependence should
> > play that much against it.
> > 
> > However, I agree with Sean and Jay that the benefit is unclear -- the few
> > features that Mimic brings seem to be outweighed by the increased risk of
> > introducing a delta between the implementation and the mock. If the main
> > benefit is that it's used in other Rackspace projects for testing (like Ben
> > said), I'm not sure that makes a compelling argument for the rest of the
> > community...
> No, that is not the main benefit, at all. Ben isn't involved in Ironic
> and until now has had nothing to do with this work to add mimic here, so
> I'm not sure where he got that impression from, or why he's speaking on
> our behalf as to the goals here.
> As pointed out before, the risk of a delta between the mocks in mimic
> and reality is identical to the risk of a delta between the mocks in a
> client's unit tests and reality, so I don't see a particular downside
> there.
> Again, I think "benefit is unclear" isn't a valid reason to block this,
> so unless someone posts a revert we're going to move forward with this.

I have not made a decision myself about whether it's right to go
ahead or not, but if we need to have a revert in place to continue
the conversation, I'll do that.  Please see
https://review.openstack.org/#/c/265416/ as the patch to revert
adding mimic.


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