Re: [netmod] instance data new backward compatibility text

Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> Mon, 25 March 2019 23:22 UTC

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Date: Tue, 26 Mar 2019 00:22:40 +0100
From: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>
To: =?utf-8?Q?Bal=C3=A1zs?= Lengyel <balazs.lengyel@ericsson.com>
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Subject: Re: [netmod] instance data new backward compatibility text
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Your rules are use case specific and I am not convinced they are
applying to all use cases. It should be a perfectly valid use case to
store snapshots of <running> in instance data files. Your rules do not
make sense here and I do not think this is a valid usage of the SHOULD
mechanism.

/js

On Mon, Mar 25, 2019 at 11:01:52PM +0000, Balázs Lengyel wrote:
>    Hello Jurgen,
> 
>    I don't think these rules are Ericsson specific. In some of our most
>    important use-cases (UC1, UC2, UC6) changing the keys would lead to
>    problems.
> 
>    UC1: If you document server capabilities using ietf-yang-library the name
>    of the module sets may be/should be meaningful. It might be used by the
>    NMS to compare the capabilities of different versions of the YANG server;
>    changing keys without a reason will mislead the NMS into assuming the
>    server capabilities changed..
> 
>    UC2: Preloading default configuration data. E.g. If you change the
>    identifier of NACM ruleset, then during upgrade it might be loaded again
>    as the server can not detect, that this is the same ruleset that is
>    already in the datastore.
> 
>    UC6:Â Storing diagnostics data. If you change the keys used in diagnostic
>    data, comparing values before and after the key change will be difficult.
> 
>    And yes as we were using instance data for the last then years, we did
>    have a lot of problem with people changing the keys without considering
>    compatibility effects.
>    I agree that this is not always a problem, so I only used SHOULDÂ (and not
>    MUST) in the text.
> 
>    regards Balazs
> 
> 
>    On 2019. 03. 25. 23:16, Juergen Schoenwaelder wrote:
> 
>  On Mon, Mar 25, 2019 at 09:59:43PM +0000, Balázs Lengyel wrote:
> 
>  Hello Jurgen,
> 
>  You are right that this is important mostly for instance data prepared as a
>  design/implementation activity; while not relevant for data coming from the
>  node.
>  I will add it.
> 
>  However in the first case it is vital!
> 
>  For config files, and also for file documenting server capabilities we have
>  had MANY problems with people changing the key values/identities of list
>  entries.
>  They think it is a nice idea to provide better, more meaningful key values;
>  however the NMS designers use these key values to detect changes; also
>  during an upgrade process if a default configuration file is loaded again
>  with slightly changed key values, then e.g. access control rules become
>  duplicated.
> 
> 
>  The conditions under which it is meaningful to change keys and when it
>  is not appropriate are very application specific.  You may have
>  specific use cases at Ericsson where you want internal regulations but
>  I do not think this leads to meaningful rules outside your specific
>  application scenario.
> 
>  /js
> 
> 
>  --
>  Balazs Lengyel                       Ericsson Hungary Ltd.
>  Senior Specialist
>  Mobile: +36-70-330-7909              email: [1]Balazs.Lengyel@ericsson.com
> 
> References
> 
>    Visible links
>    1. mailto:Balazs.Lengyel@ericsson.com



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-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
Fax:   +49 421 200 3103         <https://www.jacobs-university.de/>