[openstack-dev] [oslo] Can we stop global requirements update?

Doug Hellmann doug at doughellmann.com
Fri May 19 16:37:50 UTC 2017

Excerpts from Mehdi Abaakouk's message of 2017-05-19 10:23:09 +0200:
> On Thu, May 18, 2017 at 03:16:20PM -0400, Mike Bayer wrote:
> >
> >
> >On 05/18/2017 02:37 PM, Julien Danjou wrote:
> >>On Thu, May 18 2017, Mike Bayer wrote:
> >>
> >>>I'm not understanding this?  do you mean this?
> >>
> >>In the long run, yes. Unfortunately, we're not happy with the way Oslo
> >>libraries are managed and too OpenStack centric. I've tried for the last
> >>couple of years to move things on, but it's barely possible to deprecate
> >>anything and contribute, so I feel it's safer to start fresh and better
> >>alternative. Cotyledon by Mehdi is a good example of what can be
> >>achieved.
> >
> >
> >here's cotyledon:
> >
> >https://cotyledon.readthedocs.io/en/latest/
> >
> >
> >replaces oslo.service with a multiprocessing approach that doesn't use 
> >eventlet.  great!  any openstack service that rides on oslo.service 
> >would like to be able to transparently switch from eventlet to 
> >multiprocessing the same way they can more or less switch to mod_wsgi 
> >at the moment.   IMO this should be part of oslo.service itself.   
> I have quickly presented cotyledon some summit ago, we said we will wait
> to see if other projects want to get rid of eventlet before adopting
> such new lib (or merge it with oslo.service).
> But for now, the lib is still under telemetry umbrella.
> Keeping the current API and supporting both are (I think) impossible.
> The current API is too eventlet centric. And some applications rely
> on implicit internal contract/behavior/assumption.
> Dealing about concurrent/thread/signal safety in multithreading app or
> eventlet app is already hard enough. So having the lib that deals with
> both is even harder. We already have oslo.messaging that deals with
> 3 threads models, this is just an unending story of race conditions.
> Since a new API is needed, why not writing a new lib. Anyways when you
> get rid of eventlet you have so many thing to change to ensure your
> performance will not drop. Changing from oslo.service to cotyledon is
> really easy on the side.
> >Docs state: "oslo.service being impossible to fix and bringing an 
> >heavy dependency on eventlet, "  is there a discussion thread on that?
> Not really, I just put some comments on reviews and discus this on IRC.
> Since nobody except Telemetry have expressed/try to get rid of eventlet.
> For the story we first get rid of eventlet in Telemetry, fixes couple of
> performance issue due to using threading/process instead
> greenlet/greenthread.
> Then we fall into some weird issue due to oslo.service internal
> implementation. Process not exiting properly, signals not received,
> deadlock when signal are received, unkillable process,
> tooz/oslo.messaging heartbeat not scheduled correctly, worker not
> restarted when they are dead. All of what we expect from oslo.service
> was not working correctly anymore because we remove the line
> 'eventlet.monkeypatch()'.
> For example, when oslo.service receive a signal, it can arrive on any
> thread, this thread is paused, the callback is run in this thread
> context, but if the callback try to discus to your code in this thread,
> the process lockup, because your code is paused. Python
> offers tool to avoid that (signal.set_wakeup_fd), but oslo.service don't
> use it. I have tried to run callbacks only on the main thread with
> set_wakeup_fd, to avoid this kind of issue but I fail. The whole
> oslo.service code is clearly not designed to be threadsafe/signalsafe.
> Well, it works for eventlet because you have only one real thread.
> And this is just one example on complicated thing I have tried to fix,
> before starting cotyledon.
> >I'm finding it hard to believe that only a few years ago, everyone saw 
> >the wisdom of not re-implementing everything in their own projects and 
> >using a common layer like oslo, and already that whole situation is 
> >becoming forgotten - not just for consistency, but also when a bug is 
> >found, if fixed in oslo it gets fixed for everyone.
> Because the internal of cotyledon and oslo.service are so different.
> Having the code in oslo or not doesn't help for maintenance anymore.
> Cotyledon is a lib, code and bugs :) can already be shared between
> projects that doesn't want eventlet.

Yes, I remember discussing this some time ago and I agree that starting
a new library was the right approach. The changes needed to make
oslo.service work without eventlet are too big, and rather than have 2
separate implementations in the same library a second library makes

> >An increase in the scope of oslo is essential to dealing with the 
> >issue of "complexity" in openstack. 
> Increasing the scope of oslo works only if libs have maintainers. But
> most of them lack of people today. Most of oslo libs are in maintenance
> mode. But that another subject.
> > The state of openstack as dozens 
> >of individual software projects each with their own idiosyncratic 
> >quirks, CLIs, process and deployment models, and everything else that 
> >is visible to operators is ground zero for perceived operator 
> >complexity.
> Cotyledon have been written to be Openstack agnostic. But I have also
> write an optional module within the library to glue oslo.config and
> cotyledon. Mainly to mimic the oslo.config options/reload of
> oslo.service and make operators experience unchanged for Openstack
> people.

That sounds like a good approach.


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