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

Thierry Carrez thierry at openstack.org
Fri Jan 8 10:00:35 UTC 2016

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:


> 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...

Thierry Carrez (ttx)

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