Re: [netmod] WG Last Call: draft-ietf-netmod-yang-instance-file-format-06

[Schönwälder, Jürgen <[e-mail]>]

On Tue, Jan 07, 2020 at 12:41:23PM +0000, Kent Watsen wrote:
> 
> This begins a two-week Working Group Last Call (WGLC) on draft-ietf-netmod-yang-instance-file-format-06.  The WGLC ends on Jan 21.  Please send your comments to the working group mailing list.
> 
> Positive comments, e.g., "I've reviewed this document and believe it is ready for publication", are welcome!  This is useful and important, even from authors.  Objections, concerns, and suggestions are also welcomed at this time.
>

I have reviewed draft-ietf-netmod-yang-instance-file-format-06. I
believe this is an important document but not quite ready yet. Most of
the points I am raising below should, however, be easy to resolve,
many concern terminology and writing consolidation and do not affect
the technical solution.

/js

* Abstract

  I think we should avoid referring to some <get> operation. Here is a
  proposal of a rewrite:

OLD

   running server available.  This document specifies a standard file
   format for YANG instance data (which follows the syntax and semantic
   from existing YANG models, re-using the same format as the reply to a
   <get> operation/request) and annotates it with metadata.

NEW

   running server available.  This document specifies a standard file
   format for YANG instance data, which follows the syntax and semantic
   of existing YANG models, and annotates it with metadata.

* Terminology

  - Add missing dots (full stops) at the end of sentences

  - I fail to see the difference between 'content-schema' and 'content
    defining YANG module(s)'. The 'content-schema' is already a set of
    YANG modules. I suggest to remove 'Content defining YANG module(s)
    as it is not a necessary term. Rewrite all places where the phrase
    'content defining YANG modules' is used.

  - Is "YANG Instance Data" a newly defined term? It's introduction
    does not follow the colon style. I also wonder why we need this
    term. Why is YANG in there? I would prefer to have this defined in
    RFC 7950 terms. Is 'instance data' a collection of instantiated
    'data nodes'? Perhaps then we should do the following and move
    this up to the first definition, so we define instance data first,
    then instance data set, and finally instance data file.

    OLD

   YANG Instance Data, or just instance data for short, is data that
   could be stored in a datastore and whose syntax and semantics is
   defined by YANG models.

    NEW

   Instance Data: A collection of instantiated data nodes.

* Introduction

  - It seems UC5 subsumes UC4.

  - One could add UCx: Storing instance data used as test cases but
    then this list of use cases does not need to be exhaustive (means
    I do not care much).

  - Is it necessary to describe P2 in terms of (presumably) NETCONF
    operations? I would prefer to have the document written in a
    protocol agnostic style. Perhaps simply drop "similar to the
    response of a <get> operation/request".

  - P4: What is 'many'? Or did you want to use 'multiple'?

* Instance Data File Format

  - Replace "real data" with instance data

  OLD

    "real data" that we want to document/provide.

  NEW

    instance data that we want to document/provide.

  - I do not understand that text about the default attribute. Section
    4.8.9 defines a query parameter, not an attribute. And I do not
    know how that fits into content data.

  - Similarly, I do not understand why implementation specific
    metadata may be included in the content-data. This seems to be the
    wrong place, no? Should metadata not go into the header?

  - Why MUST XML attributes be ignored, why is there no text about
    unknown JSON data, 'attributes' (or annotations)? What should
    implementations generally do about unknown elements, attributes,
    objects, arrays, ...)? Why are we specific about only one specific
    case?

  - References may be helpful in this sentence since <get-data> is not
    part of the original NETCONF specification:

   The content-data part will be very similar to the result returned for
   a NETCONF <get-data> or for a RESTCONF get operation.

    It is unclear what "will be very similar" really means but perhaps
    this is clarified later. If not, this sentence says nothing in
    terms of a technical specification.

  - Does the following sentence imply that any additional data in an
    instance file renders the instance file useless?

   The content-data part MUST conform to the content-schema.

  - You first write that instance data MUST conform to the schema and
    two paragraphs later you state that instance data MAY be partial,
    i.e., it MAY NOT conform to the content-schema. Perhaps I have an
    idea what you wanted to say but the text that is written here is
    a contradiction.

  - The introduction contains several MAYs and MUSTS that are not
    understandable yet and they do not seem to belong into an
    'Introduction' in the first place.

  - Why is EXTERNAL in all caps but Inline in capitalized form?  In
    the YANG definitions, EXTERNAL seems to be uri. I think we reduce
    ambiguity by being consistent with how we name things.

  - What is a 'real-life YANG module'?

  - 3.1.1 How are the details specified in the anydata? Perhaps a
    forward reference might help. What are 'version labels'?

  - 3.1.2 What is a 'list of content'? Which revision is used? What
    about these 'version labels' here?

  - 3.2 I do not understand the example. Has this been validated?  As
    far as I can tell, the ietf-yang-library defines modules-state and
    not module-state. This inconsistency shows up multiple times.

  - I like to understand why we need several methods to specify the
    schema. Having N solution is always bad for interoperability and
    also for maintainability. Perhaps the WG failed to reach consensus
    on a single solution.  Or there are strong technical reasons - but
    then they should be clearly stated. What are implementations
    expected to support, all methods? Or whatever the implementer
    prefers? How do we achieve interoperability across tools?

* Data Life Cycle

  - I am not sure the first paragraph is needed.

  - In the second paragraph, I like to see some discussion of snapshot
    consistency.  How much consistency can be expected? Are there
    indicators for the level of consistency? I would remove the
    sentence about "valid values can be retrieved at run-time" as this
    is obvious but then I am not sure why 'valid' values? Perhaps the
    authors meant 'current' values?

  - How do I implement the "SHOULD be described"? The default is that
    data can change, only in rare cases data is static. But how does a
    tool creating instance data know 'when and how' data changes in the
    future? I suggest to remove the SHOULD. The text saying that instance
    data is a snapshot is in my view sufficient.

  - This section talks about YANG instance data but it likely should
    talk about YANG instance data sets.

* Delivery of Instance Data

  - Why do we need this SHOULD? I do not think we should use RFC 2119
    keywords to define how organizations may use the instance data
    format. My proposal is to delete this entire section.

* Backwards Compatibility

  - I do not think 'managed entity' is a YANG term.

  - I think this text is use case specific and the items are kind of
    conflicting with each other (2nd says changing the semantics of a
    list should lead to a change of the key while the 1st suggests
    that changing keys may lead to misinterpretation of something
    being new).

  - My proposal is to simply drop this entire section. If use case
    specific text is needed, add it to the use cases in the appendix.

* YANG Model

  - How is the inline-content-schema feature used? Which component
    does indicate that inline content-schema is supported? Do all
    implementations have to support simplified-inline? If
    inline-schema is used, how do I find out which schema formats are
    supported? The more formats there are, the more interoperability
    issues will arise.

* Security Considerations

  - "is designed as a wrapper" - what does this tell me? I suggest to
    rewrite the first paragraph and to remove this phrase or to explain
    what it means.

  - Why is the header part not security sensitive? Almost all data is
    security sensitive in certain situations.

  - I would prefer if the text would not use the phrase "result of a
    <get> operation". As stated before, I like to see things written
    in protocol neutral forms.

  - Since instance data files may require protection, is there any
    recommendation how to do this, e.g., by wrapping everything into a
    cryptographic message syntax or so? It would be important in
    certain use cases to be able to verify that instance data is
    authentic (i.e., it is signed by the original source). In other
    cases, it may be crucial to protect the instance data itself
    against occasional readers.

  - It may be useful to explain that data in instance data sets may
    have been filtered by access control rules like NACM and that data
    in instance data sets itself won't be filtered anymore by access
    control rules like NACM. In other words, if I take snapshots and
    stored them as instance data files, these snapshots may leak
    information that is otherwise protected. Hence it is important
    that NACM rules and file access control rules are consistent.

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
Fax:   [phone]         <https://www.jacobs-university.de/>