[openstack-dev] [keystone][congress][group-policy] Fetching policy from a remote source

Tim Hinrichs thinrichs at vmware.com
Mon Mar 16 18:59:33 UTC 2015

Hi Adam,

For the most part we've been looking at Congress policy as complementary to Oslo policy, so we haven’t yet tried to incorporate Oslo policy into Congress (though I did some experiments with that a while back).   But looking forward, it would definitely be convenient if there were some way to fetch Oslo policy from each of the components.

More inline...

> On Mar 16, 2015, at 8:10 AM, Adam Young <ayoung at redhat.com> wrote:
> 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.

I thought each service would provide an API endpoint that would allow us to fetch their policy.json.  Why would we go through Keystone?

> 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.

I’m guessing performance won’t be a problem.  Policy.json is small, and there are likely few services listening to updates.  

Is the *content* of policy.json something sensitive that needs high security?  Months ago there was a thread about building a tool for analyzing policy.json to tell people which groups they would need to execute a given API call.  Wouldn’t that mean we’re probably not too concerned about people seeing the contents of policy.json?   I’m not saying we should broadcast policy.json to everyone who wants it, but it’s not clear to me we need to worry about protecting policy.json any more than administrator-level data returned by today’s API calls.

> 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?

If there were an API call for fetching policy, I would expect it to be protected just like any other API call.  And sure we’d provide whatever credentials are necessary to make that call.


> 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?
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