At the summit session last week for group-based policy, there were many 
concerns voiced about the approach being undertaken.  I think those concerns 
deserve a wider audience, and I'm going to highlight some of them here.

The primary concern seemed to be related to the complexity of the approach 
implemented for the POC.  A number of session participants voiced concern that 
the simpler approach documented in the original proposal [1] (described in the 
section titled 'Policies applied between groups') had not been implemented in 
addition to or instead of what appeared in the POC (described in the section 
titled 'Policies applied as a group API').  The simpler approach was considered 
by those participants as having the advantage of clarity and immediate 
usefulness, whereas the complex approach was deemed hard to understand and 
without immediate utility.

A secondary but no less important concern is related to the impact on Neutron 
of the approach implemented in the POC.  The POC was developed monolithically, 
without oversight through gerrit, and the resulting patches were excessive in 
size (~4700 [2] and ~1500 [3] lines).  Such large patches are effectively 
impossible to review.  Even broken down into reviewable chunks, though, it does 
not seem realistic to target juno-1 for merging this kind of complexity.  The 
impact on stability could be considerable, and it is questionable whether the 
necessary review effort should be devoted to fast-tracking group-based policy 
at all, let alone an approach that is considered by many to be unnecessarily 
complicated.  

The blueprint for group policy [4] is currently listed as a 'High' priority.  
With the above concerns in mind, does it make sense to continue prioritizing an 
effort that at present would seem to require considerably more resources than 
the benefit it appears to promise?


Maru

1: https://etherpad.openstack.org/p/group-based-policy
2: https://review.openstack.org/93853
3: https://review.openstack.org/93935
4: https://blueprints.launchpad.net/neutron/+spec/group-based-policy-abstraction

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