[openstack-dev] Congress: an open policy framework

Flavio Percoco flavio at redhat.com
Thu Nov 14 14:05:46 UTC 2013

On 14/11/13 04:40 -0800, Morgan Fainberg wrote:
>On Wed, Nov 13, 2013 at 10:40 AM, Tim Hinrichs <thinrichs at vmware.com> wrote:
>> We're just getting started with Congress and understanding how it will integrate with the OS ecosystem, but here's our current thinking about how Congress relates to Oslo's policy engine and to Keystone.  Comments and suggestions are welcome.
>> Congress and Oslo
>> --------------------
>> Three dimensions for comparison: policy language, data sources, and policy engine.
>> We've always planned to make Congress compatible with existing policy languages like the one in oslo.  The plan is to build a front-end for a number of policy languages/formats, e.g. oslo-policy language, XACML, JSON, YAML, SQL, etc.  The idea being that the syntax/language you use is irrelevant as long as it can be mapped into Congress's native policy language.  As of now, Congress is using Datalog, which is a variant of SQL and is at least as expressive as all of the policy languages we've run across in the cloud domain, including the oslo-policy language.
>> In terms of the data sources you can reference in the policy, Congress is designed to enable policies that reference arbitrary data sources in the cloud.  For example, we could write a Nova authorization policy that permits a new VM to be created if that VM is connected to a network owned by a tenant (info stored in Neutron) where the VM owner (info in the request) is in the same group as the network owner (info stored in Keystone/LDAP).  Oslo's handles some of these data sources with its terminal rules, but it's not involved in data integration to the same extent Congress is.
>> In terms of policy engines, Congress is intended to enforce policies in 2 different ways: proactively (stopping policy violations before they occur) and reactively (acting to eliminate a violation after it occurs).  Ideally we wouldn't need reactive enforcement, but there will always be cases where proactive enforcement is not possible (e.g. a DOS attack brings app latencies out of compliance).  The oslo-engine does proactive enforcement only--stopping API calls before they violate the policy.
>Does this mean all policy decisions need to ask this new service?
>There are many policy checks that occur across even a given action (in
>some cases).  Could this have a significant performance implication on
>larger scale cloud deployments?  I like the idea of having reactive
>(DOS prevention) policy enforcement as well as external (arbitrary)
>data to help make policy decisions, I don't want to see Congress be
>limited in deployment because large scale clouds getting bottle-necked
>trying to communicate with it.

This is exactly what worries me about Congress. I mentioned in my last
email that some kind of 'local' cache managed by the Confress library
is a must to avoid the performance penalty.

>There might be some value  to seeing some work being done to provide
>more information to Keystone, but I think this will become more
>apparent as Congress develops.



Flavio Percoco

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