Hi Prabhakar,
Thanks for the feedback. I'd be interested to hear what other policy types you
have in mind.
To answer your questions...
We're planning on extending our policy language in such a way that you can use
Python functions as conditions ("<atom>" in the grammar) in rules. That's on my
todo-list but didn't mention it yesterday as we were short on time. There will
be some syntactic restrictions so that we can properly execute those Python
functions (i.e. we need to always be able to compute the inputs to the
function). I had thought it was just an implementation detail I hadn't gotten
around to (all Datalog implementations I've seen have such things), but it
sounds like it's worth writing up a proposal and sending it around before
implementing. If that's a pressing concern for you, let me know and I'll bump
it up the stack (a little). If you'd like, feel free to draft a proposal (or
remind me to do it once in a while).
As for actions, I typically think of them as API calls to other OS components
like Nova. But they could just as easily be Python functions. But I would want
to avoid an action that changes Congress's internal data structures directly
(e.g. adding a new policy statement). Such actions have caused trouble in the
past for policy languages (though for declarative programming languages like
Prolog they are less problematic). I don't think there's anyway we can stop
people from creating such actions, but I think we should advocate against them.
Tim
----- Original Message -----
From: "prabhakar Kudva" <[email protected]>
To: "OpenStack Development Mailing List (not for usage questions)"
<[email protected]>
Sent: Wednesday, March 12, 2014 11:34:04 AM
Subject: Re: [openstack-dev] [Congress] Policy types
Hi Tim, All,
I was in the discussion yesterday (kudva), and would like to start gradually
contributing to the code base.
So, this discussion below is based on my limited exploration of Congress
code, running it. I am trying some small pieces to implement to familiarize.
Please view it as such. As I start adding code, I am sure, my thoughts will
be more evolved.
I agree with the three types you outline. I also agree that these will grow.
We are already thinking of expanding congress for various other types of
policies. But those would be a manageable start.
Regarding the comment below. I was wondering if all conditions, and actions
could be both:
1. python functions (for conditions they eval
2. policy primitives.
The advantage of 1, is that it is just executed and a True or False returned
by Python for conditions. For actions, python functions are executed to respond
to conditions.
This controls the growth of policies and adding more primitives, and makes it
flexible (say
to use alarms, monitors, os clients, nova actions etc).
The advantage of 2, is the ability to use unification (as in unify.py) and do
some logic reduction. This gives us the full strength of extensive and mature
logic reasoning and reduction methods.
One possibility is that it checks which one the two it is and does the
appropriate
evaluation for condition and action.
>There are drawbacks to this proposal as well.
>- We will have 3 separate policies that are conceptually very similar. As the
>policies grow larger, it will become >increasingly difficult to keep the
>policies synchronized. This problem can be mitigated to some extent by having
>>all 3 share a library of policy statements that they all apply in different
>ways (and such a library mechanism is >already implemented).
>- As cloud services change their behavior, policies may need to be re-written.
>For example, right now Nova does >not consult Congress before creating a VM;
>thus, to enforce policy surrounding VMs, the best we could do is >write a
>Condition-Action policy that adjusts VM configuration when it learns about new
>VMs being created. If we >later make Nova consult with Congress before
>creating a VM, we need to write an Access-control policy that puts >the proper
>controls in place.
Thanks,
Prabhakar Kudva
Date: Wed, 12 Mar 2014 10:05:23 -0700
From: [email protected]
To: [email protected]
Subject: [openstack-dev] [Congress] Policy types
Hi all,
We started a discussion on IRC yesterday that I'd like to continue. The main
question is what kind of policy does a Congress user actually write? I can see
three options. The first two focus on actions (API calls that make changes to
the state of the cloud) and the last focuses on just the cloud state. (By
"state of the cloud" I mean all the information Congress can see about all the
cloud services it is managing, e.g. all the information we can get through API
calls to Nova, Neutron, Cinder, Heat, ...).
1) Access Control (e.g. Linux, XACML, AD): which *actions* can be performed by
other cloud services (for each state of the cloud)
2) Condition Action: which *actions* Congress should execute (for each state of
the cloud)
3) Classification (currently supported in Congress): which *states* violate
real-world policy. [For those of you who have read docs/white-papers/etc. I'm
using "Classification" in this note to mean the combination of the current
"Classification" and "Action Description" policies.]
The important observation is that each of these policies could contain
different information from each of the others.
- Access Control vs Condition Action. The Access Control policy tells *other
cloud services* which actions they are *allowed* to execute. The Condition
Action policy tells *Congress* which actions it *must* execute. These policies
differ because they constrain different sets of cloud services.
- Access Control vs. Classification. The Access Control policy might permit
some users to violate the Classification policy in some situations (e.g. to fix
violation A, we might need to cause violation B before eliminating both). These
policies differ because a violation in one policy might be be a violation in
the other.
- Classification vs. Condition Action. The Classification policy might imply
which actions *could* eliminate a given violation, but the Condition Action
policy would dictate which of those actions *should* be executed (e.g. the
Classification policy might tell us that disconnecting a network and deleting a
VM would both eliminate a particular violation, but the Condition Action policy
would tell us which to choose). And the Condition Action policy need not
eliminate all the violations present in the Classification policy. Again these
policies differ because a violation in one policy might not be a violation in
the other.
I'm proposing that for the first release of Congress we support all 3 of these
policies. When a user inserts/deletes a policy statement, she chooses which
policy it belongs to. All would be written in basically the same syntax but
would be used in 3 different scenarios:
- Prevention: If a component wants to consult Congress before taking action to
see if that action is allowed, Congress checks the Access Control policy.
- Reaction: When Congress learns of a change in the cloud's state, it checks
the Condition Action policy to see which actions should be executed (if any).
- Monitoring: If a user wants to simply check if the cloud's state is in
compliance and monitor compliance over time, she writes and queries the
Classification policy.
There are several benefits to this proposal.
- It allows users to choose any of the policy types, if they only want one of
them. From our discussions with potential users, most seem to want one of these
3 policy types (and are uninterested in the others).
- It makes the introduction to Congress relatively simple. We describe 3
different uses of policy (Prevention, Reaction, Monitoring) and then explain
which policy to use in which case.
- This allows us to focus on implementing a single policy-engine technology (a
Datalog policy language and evaluation algorithms), which gives us the
opportunity to make it solid.
There are drawbacks to this proposal as well.
- We will have 3 separate policies that are conceptually very similar. As the
policies grow larger, it will become increasingly difficult to keep the
policies synchronized. This problem can be mitigated to some extent by having
all 3 share a library of policy statements that they all apply in different
ways (and such a library mechanism is already implemented).
- As cloud services change their behavior, policies may need to be re-written.
For example, right now Nova does not consult Congress before creating a VM;
thus, to enforce policy surrounding VMs, the best we could do is write a
Condition-Action policy that adjusts VM configuration when it learns about new
VMs being created. If we later make Nova consult with Congress before creating
a VM, we need to write an Access-control policy that puts the proper controls
in place.
These drawbacks were the original motivation for supporting only the
Classification policy and attempting to derive the Access Control and Condition
Action policies from it. But given that we can't always derive the proper
Access Control and Condition Action policies from the Classification policy, we
will eventually need support for all 3. In addition, the technical complexity
of supporting all 3 is much lower than supporting just the Classification
policy and deriving the others.
I'll stop there for now.
Comments, thoughts, questions?
Tim
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