All-

tl;dr

* Group Based Policy API is the kind of experimentation we be should attempting.
* Experiments should be able to fail fast.
* The master branch does not fail fast.
* StackForge is the proper home to conduct this experiment.


Why this email?
---------------
Our community has been discussing and working on Group Based Policy (GBP) for 
many months.  I think the discussion has reached a point where we need to 
openly discuss a few issues before moving forward.  I recognize that this 
discussion could create frustration for those who have invested significant 
time and energy, but the reality is we need ensure we are making decisions that 
benefit all members of our community (users, operators, developers and vendors).

Experimentation
----------------
I like that as a community we are exploring alternate APIs.  The process of 
exploring via real user experimentation can produce valuable results.  A good 
experiment should be designed to fail fast to enable further trials via rapid 
iteration.

Merging large changes into the master branch is the exact opposite of failing 
fast.

The master branch deliberately favors small iterative changes over time.  
Releasing a new version of the proposed API every six months limits our ability 
to learn and make adjustments.

In the past, we’ve released LBaaS, FWaaS, and VPNaaS as experimental APIs.  The 
results have been very mixed as operators either shy away from testing/offering 
the API or embrace the API with the expectation that the community will provide 
full API support and migration.  In both cases, the experiment fails because we 
either could not get the data we need or are unable to make significant changes 
without accepting a non-trivial amount of technical debt via migrations or 
draft API support.

Next Steps
----------
Previously, the GPB subteam used a Github account to host the development, but 
the workflows and tooling do not align with OpenStack's development model. I’d 
like to see us create a group based policy project in StackForge.  StackForge 
will host the code and enable us to follow the same open review and QA 
processes we use in the main project while we are developing and testing the 
API. The infrastructure there will benefit us as we will have a separate review 
velocity and can frequently publish libraries to PyPI.  From a technical 
perspective, the 13 new entities in GPB [1] do not require any changes to 
internal Neutron data structures.  The docs[2] also suggest that an external 
plugin or service would work to make it easier to speed development.

End State
---------
APIs require time to fully bake and right now it is too early to know the final 
outcome.  Using StackForge will allow the team to retain all of its options 
including: merging the code into Neutron, adopting the repository as 
sub-project of the Network Program, leaving the project in StackForge project 
or learning that users want something completely different.  I would expect 
that we'll revisit the status of the repo during the L or M cycles since the 
Kilo development cycle does not leave enough time to experiment and iterate.


mark

[1] 
http://git.openstack.org/cgit/openstack/neutron-specs/tree/specs/juno/group-based-policy-abstraction.rst#n370
[2] 
https://docs.google.com/presentation/d/1Nn1HjghAvk2RTPwvltSrnCUJkidWKWY2ckU7OYAVNpo/edit#slide=id.g12c5a79d7_4078
[3]
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