Open Stack

Oslo policy has been released as a stand alone library.  This is great, 
in that the rules engine is relatively non-applicaition specific, and I 
assume that all of the policy based project are planning to migrate over 
to using the policy library instead of the incubated version.

Part of the push toward a more dynamic policy mechanism is figuring out 
how to fetch and cache the policy files from Keystone.  I suspect that 
the other services have the same issue.

1.  How long should a service hold on to the cached version of the 
policy file?
2.  How can we avoid the stampeding herd if Keystone pushes out a 
notification change event?
3.  How do we securely cache the file and still make it possible to debug.

The PKI tokens have a lot of these same issues, and have a one-off 
mechanism for handling it.  We should probably look in to commonizing 
this function.

There general mechanism should be "fetch and cache" but I think it 
should not be tied to keystone token validation so much as capable of 
using it if necessary.  I'm guessing that access to policy rules are 
typically controlled by auth token validated services.  Is this correct?

Maybe the right level of abstraction is a callback function for fetching 
the file to be cached, with the default being something that uses 
python-requests, and then an  auth plugin based alternative for those 
that require Keystone tokens.

Before I go off and write a spec, I'd like to know what the prior art is 
here.  I'd also like to know if there oslo policy library is part of the 
plans for the other groups that are doing policy based work?