[i2rs] Review of draft-ietf-i2rs-ephemeral-state-11

[Robert Wilton <[e-mail]>]

Hi,

I've reviewed draft-ietf-i2rs-ephemeral-state-11 and given a few minor 
comments below.  Generally I think that I understand the requirements 
stated in this document.

Minors comments:

1) Ephemeral-REQ-01 (page 5):

    Ephemeral-REQ-01: I2RS requires ephemeral state; i.e. state that does
    not persist across reboots.  If state must be restored, it should be
    done solely by replay actions from the I2RS client via the I2RS
    agent.

The architecture document indicates that the ephemeral state would (or 
is that may) also be lost on other circumstances such as process restart 
of the I2RS agent.  Does this need to be clarified in the requirement?  E.g.

    Ephemeral-REQ-01: I2RS requires ephemeral state; i.e. state that MUST
    NOT persist across reboots of the device or I2RS Agent subsystem. If
    state must be restored, it should be done solely by replay actions
    from the I2RS client via the I2RS agent.


2) Hierarchy: (page 5)
Based on the previous description, I would possibly split 
Ephemeral-REQ-06 up into the following requirements:

Old (from ephemeral-state:10):

    Ephemeral-REQ-06: The ability to augment an object with appropriate
    YANG structures that have the property of being ephemeral.  An object
    defined as any one of the following: yang module, submodule or
    components of submodule, or schema node.

Old (from ephemeral-state-11):

    Ephemeral-REQ-06: The ability to augment Yang schema nodes with
    additional Yang Schema nodes that have the property of being
    ephemeral.

Proposed:

    Ephemeral-REQ-06:
  
    1. The ability to define a YANG module or submodule schema that
    only contains data nodes with the property of being ephemeral.

    2. The ability to augment a YANG data model with additional YANG
    schema nodes that have the property of being ephemeral.


3) Ephemeral-REQ-07: (page 6):

    Ephemeral-REQ-07: Ephemeral configuration state could override
    overlapping local configuration state, or vice-versa.
    Implementations MUST provide a mechanism to choose which takes
    precedence.  This mechanism MUST include local configuration (policy)
    and MAY be provided via the I2RS protocol mechanisms.

I note that this requirement doesn't specify the scope of whether the 
override mechanism should operate globally or on a per data node basis.  
I'm not sure whether this needs to be clarified - since the text in the 
architecture document makes it pretty clear that a global level 
resolution is sufficient.


4) Ephemeral-REQ-08: (page 6):
Similar to Juergen's comments, I'm concerned about the 
writable/non-writable requirement.


    Ephemeral-REQ-08: Yang MUST have a way to indicate in a data model
    that schema nodes have the following properties: ephemeral, writable/
    not-writable, and status/configuration.

I'm somewhat adverse to writable operational state, and hence I would 
prefer if this requirement was watered down to something like:

    Ephemeral-REQ-08: In addition to config true/false, there MUST be a
    way to indicate that YANG schema nodes represent ephemeral state.
    It is desirable to allow for, and have to way to indicate, config
    false YANG schema nodes that are writable operational state.


5) Ephemeral-Req-12, page 7:
Presumably the requirement is that the notification must indicate the 
node that we involved in the collision?  I.e. it isn't sufficient to 
just signal to the client that there has been a collision with some of 
their configuration?

    Ephemeral-REQ-12: When a collision occurs as two clients are trying
    to write the same data node, this collision is considered an error
    and priorities were created to give a deterministic result.  When
    there is a collision, a notification MUST BE sent to the original
    client to give the original client a chance to deal with the issues
    surrounding the collision.  The original client may need to fix their
    state.

Should this be made explicit?  E.g. perhaps:

    Ephemeral-REQ-12: When a collision occurs as two clients are trying
    to write the same data node, this collision is considered an error
    and priorities were created to give a deterministic result.  When
    there is a collision, a notification (indicating which data node the
    collision occurred on) MUST BE sent to the original client to give
    the original client a chance to deal with the issues surrounding
    the collision.  The original client may need to fix their state.


6) Ephemeral-REQ-14, page 7:
I would suggest potentially rewording this to make the requirement and 
leeway on the solution more explicit.

    Ephemeral-REQ-14: If two clients have the same priority, the
    architecture says the first one wins.  The I2RS protocol has this
    requirement to prevent oscillations between clients.  If one uses the
    last wins scenario, you may oscillate.  That was our opinion, but a
    design which prevents oscillation is the key point.

Proposed alternative text:

    Ephemeral-REQ-14: A deterministic conflict resolution mechanism MUST
    be provided to handle the error scenario that two clients, with
    the same priority, update the same configuration data node.  The I2RS
    architecture gives one way that this could be achieved, by
    specifying that the first update wins.  Other solutions, that prevent
    oscillation of the config data node, are also acceptable.


Cosmetic comments:

7) Section 1. Introduction.  The requirements are no longer version 
specific, hence perhaps update the following text from:


    1.  select features from YANG, NETCONF, and RESTCONF per version of
        the I2RS protocol (See sections 4, 5, and 6)

    2.  propose additions to YANG, NETCONF, and RESTCONF per version of
        the I2RS protocol for key functions (ephemeral state, protocol
        security, publication/subscription service, traceability),

to:

    1.  select features from YANG, NETCONF, and RESTCONF for the initial
        I2RS protocol version (See sections 4, 5, and 6).

    2.  propose additions to YANG, NETCONF, and RESTCONF for the initial
        I2RS protocol version for key functions (ephemeral state, protocol
        security, publication/subscription service, traceability).


8) Section 1. introduction.  I'm not sure that this 3rd bullet is 
relevant, and possibly could be removed, although equally it doesn't 
seem to do any harm:

    3.  suggest protocol strawman as ideas for the NETCONF, RESTCONF, and
        YANG changes.



9) The document uses a mix of "Yang" and "YANG", probably should just 
use "YANG".


10) Section 3. Ephemeral State Requirements:

The document refers to "ephemeral configured state" here, but elsewhere 
(e.g. 3.4) "ephemeral configuration" or "ephemeral configuration state" 
is used.  It might be helpful for use of these terms to be consistent, I 
would suggest "ephemeral configuration" is sufficient.


11) Ephemeral-REQ-13, page 7:

Minor omission in the last sentence.

   Ephemeral-REQ-13: The requirement to support multi-headed control is
    required for collisions and the priority resolution of collisions.
    Multi-headed control is not tied to ephemeral state.  I2RS is not
    mandating how AAA supports priority.  Mechanisms which prevent
    collisions of two clients trying the same node of data are the focus.

Proposed:

   Ephemeral-REQ-13: The requirement to support multi-headed control is
    required for collisions and the priority resolution of collisions.
    Multi-headed control is not tied to ephemeral state.  I2RS is not
    mandating how AAA supports priority.  Mechanisms which prevent
    collisions of two clients trying to modify the same node of data
    are the focus.


12) Ephemeral-REQ-15, page 7:
I would suggest that it might be better to refer to "Ephemeral state" 
rather than the I2RS ephemeral data-store.

    Ephemeral-REQ-15: Section 7.9 of the [I-D.ietf-i2rs-architecture]
    states the I2RS architecture does not include multi-message atomicity
    and roll-back mechanisms.  I2RS notes multiple operations in one or
    more messages handling can handle errors within the set of operations
    in many ways.  No multi-message commands SHOULD cause errors to be
    inserted into the I2RS ephemeral data-store.

Proposed:

    Ephemeral-REQ-15: Section 7.9 of the [I-D.ietf-i2rs-architecture]
    states the I2RS architecture does not include multi-message atomicity
    and roll-back mechanisms.  I2RS notes multiple operations in one or
    more messages handling can handle errors within the set of operations
    in many ways.  No multi-message commands SHOULD cause errors to be
    inserted into the ephemeral state.


Thanks,
Rob