Re: [netmod] backward compatibility requirements in draft-verdt-netmod-yang-versioning-reqs-00

On Mon, Jul 23, 2018 at 2:50 AM, Robert Wilton <rwilton@cisco.com> wrote:

> Hi Chris, Andy,
>
>
> On 21/07/2018 17:00, Christian Hopps wrote:
>
>> As I pointed out at the mic @102 this requirement derives directly from
>> the 1.x requirement of not changing the name of the module/namespace. If
>> you allow for changing the namespace/module name for "major" (i.e.,
>> incompatible) changes (i.e., like today) then this 3.1 requirement goes
>> away.
>>
> Not sure that I agree.
>
> I think that you have made an assumption here that the server will
> continue to support both old and new major revision (with different name)
> of the module at the same time.  However, these is nothing in the existing
> YANG upgrade rules that requires that.
>
> Ultimately, there is a choice whether supporting older module versions is
> the servers problem or the clients problem, or perhaps a combination of the
> two.
>
> The aim of requirement 3.1 is to ensure that there is a standard mechanism
> available so that server implementations that want the flexibility of
> supporting older client versions have a standard way of doing so.  My
> intention is that this part of the solution would be optional to implement
> and hence decided by the market, which is why the text in the requirement
> is "to allow servers" rather than "to require servers".
>
>

API versioning is usually done on the message exchanges.
Trying to do the same for datastore contents is not going to work.
You can write the word MUST in all caps as many times as you want,
but that will not change anything.

> Thanks,
> Rob
>

Andy

>
>
>
>> I think the plan is to reword some of these to get closer to the
>> intention which I believe is to allow for smoother transition from one
>> module to the next while making incompatible but mostly non-impacting
>> changes.
>>
>> Thanks,
>> Chris.
>>
>> Andy Bierman <andy@yumaworks.com> writes:
>>
>> Hi,
>>>
>>> I strongly object to requirement 3.1:
>>>
>>>
>>>     3.1  The solution MUST provide a mechanism to allow servers to
>>>             support existing clients in a backward compatible way.
>>>
>>>
>>>
>>> This is not what servers do today at all.
>>> They provide only one version of an implemented module, as specified in
>>> RFC
>>> 7950.
>>>
>>> It is a vendor and operator decision when to upgrade a server such that
>>> non-backward compatible changes are made. They must decide if/when it is
>>> ok
>>> based on the client applications in use.
>>>
>>> This requirement says you cannot make backward-incompatible changes
>>> which completely contradicts requirements 1.1 and 1.2.
>>>
>>> IMO requirement 3.1 should be removed, or change MUST to MAY
>>>
>>>
>>> Andy
>>> _______________________________________________
>>> netmod mailing list
>>> netmod@ietf.org
>>> https://www.ietf.org/mailman/listinfo/netmod
>>>
>>
>> _______________________________________________
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>> netmod@ietf.org
>> https://www.ietf.org/mailman/listinfo/netmod
>> .
>>
>>
>