Subject: [Nfvrg] draft-irtf-nfvrg-nfv-policy-arch-03 - comments and suggestions

From: Andrew Veitch <[email-masked]>
Date: Tue, 3 May 2016 16:32:20 +0000

Hi,

I have read through the latest draft of Policy Architecture and Framework for NFV Infrastructures, and I have a number of comments and suggestions.  I hope these are found useful.  Please send feedback, if you have it.

Thanks

Andy

Andrew Veitch |Senior Architect | International Mobile: +1 (781) 366-7763 | www.Netcracker.com<http://www.netcracker.com/> | Focused Forward

Page 3.
For my first point, I think I have given it much more time than it is probably worth.  But having done so, here are my recommendations and notes on the subject.
The text includes the statement:
”… policies are used to enforce business rules and to specify resource constraints, e.g. energy, in a number of subsystems, e.g. compute, …”
I think in a typical description of policy instances, it is the sets of business rules that enforce policies, and not the other way around.
Also, the text states that the policies are used to enforce business rules and to specify resource constraints.  In this context, how is there a difference between business rules and resource constraints?  Isn’t it in the policy (business) rules that any constraints on resources are defined?
After thinking about this a bit, I think what is needed is a better description of a policy - a section with some definition of terms or a reference to one should be included.
I do think there is a generally agreed upon definition of policy, and that it is something like:
A policy is a set of (business) rules that are used to define the desired state of a system or service, where the rules may direct actions to control and maintain the system or service to ensure it is in a state compliant with the policy.
This definition could continue, to be more explicit about the impact these rules may have on resources, e.g. energy and the compute, network and other subsystems.
In ensuring systems or services are compliant with a policy, the (business) rules may describe constraints on resources, e.g. energy constraints, and for a number of subsystems, e.g. compute, storage, and network, and across the subsystems
Here is a sampling of definitions of policy:

•       In his Focale paper, Strassner says that a Policy is “A set of rules that are used to manage and control the changing and/or maintaining of the state of one or more managed objects.”

•       The SUPA WG charter states, “Policies are a set of rules that define how services are designed, delivered, and operated within an operator's networking environment. As such, policies play a critical role in the automated service delivery and operational procedures.”

•       The Openstack Congress wiki page includes this text:

“The policy language for Congress …. [is a] declarative language … The core grammar is given below.

<policy> ::= <rule>*

….

“

This shows policy is defined in terms of a set of (business) rules, and the language is declarative.

This is a long-winded way of recommending that the document be updated to provide a definition for policy before using the term, and further, to define it to align with other work, and not to describe policies as enforcing business rules.

Page 3.
“[24] is an open source project proposal  …”
This is in reference to Congress, and Congress is now more than a proposal.  I recommend changing the text to remove the word “proposal”.

Page 4.
 I do not understand the concepts of static vs. dynamic vs. autonomic policies.  These are included in the top paragraph.  I have more comments and questions on these later.

Page 4. Section 2.
“Policies define which states of deployment are in compliance, and, by logical negation, which are not.”
 I think this is unclear, “in compliance” with what?  If the definition of policy is made clearer, then I thing text like, A policy’s rules describe whether or not a deployment state is considered to be compliant with the policy, and by logical negation, when it is not.

Page 4. Section 2, continued.
“The compliance statement in a policy…
There is not definition of the term “compliance statement”, nor is it, as far as I can tell, a commonly used term.  I would recommend dropping this.  Given the context of this paragraph, I would recommend simply using the term “policy rule” or “rules of a policy”.
 "
This text could then be
The rules of a policy may describe specific actions, e.g. “…”

Having said that, I am not sure the term “action” should be used.  The example given,
“a given customer is [not allowed to deploy VNF X]”,  Q: Why the brackets?

is not a description of an action, but a declaration of when a state is or is not in compliance with the policy.  “Action” also is used in the definition of an ECA policy, where an action to be executed is included in the policy.
I would recommend simply saying a rule may reference specific resources, or quasi-specific (aka abstract) concepts.
The sum of my recommendation then, is to change the text to something like:
The rules of a policy may reference specific resources or more abstract concepts.  For example, “a given customer is not allowed to deploy VNF X”, where “VNF X” is a specific reference to a VNF instance.  The rule, “a given customer must be given platinum treatment”, includes “platinum treatment” as an abstract concept. While the first rule requires no additional translation, for the second, the implications of “platinum treatment” must be derived from additional information.

Page 4. Section 2 (3rd paragraph)
 This paragraph begins with “The actions defined in a policy…”
 Based on my earlier comments, I would recommend changing this to something like
The compliance conditions defined in a policy’s rules may be translated …

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