Hi Andy,
On 31/01/2018 09:22, Andy Bierman wrote:
On Wed, Jan 31, 2018 at 12:11 AM, Juergen Schoenwaelder
<j.schoenwael...@jacobs-university.de
<mailto:j.schoenwael...@jacobs-university.de>> wrote:
On Tue, Jan 30, 2018 at 12:35:33PM -0800, Andy Bierman wrote:
> Hi,
>
> I have some questions about these drafts.
>
> 1) what if datastore set to "conventional"?
> There are many places where a datastore-ref type is used.
> However, "conventional" is valid for base "datastore", even
though
> it is ambiguous as a datastore selector.
We can add explicit text that an identity that does not resolve to a
datastore implemented by the server results in an invalid value error.
OK
> 2) origin filter is limited to 1 source
> This filtering seems rather limited. A client must retrieve
> <with-origin> and check
> all the values in use, then make repeated requests for each
source as a
> different
> <origin-filter> leaf
If the client does <with-origin>, then it has all origin information
and it can filter locally. That said, we could make origin-filter a
leaf-list which is logically ORed so that one can retrieve
origin-filter=or:system or origin-filter=or:learned in one request.
OK
> 3) with-defaults broken
> The operational datastore does not support with-defaults.
> Instead, the client must use origin-filter=or:default or
with-origin
> and check all the origin attributes. Since a client needs
to use
> with-defaults for other datastores, this special handling of
> <operational>
> seems unhelpful.
I think the with-defaults semantics for conventional configuration
datastores are much more complicated than necessary for the
operational state datastore. Note that that the operational state
datastore reports in-use values not really defaults:
<leaf or:origin='default'>foo</leaf>
This reports that the value 'foo' is in use and that it originates
from a default value. Note that this could also be
<leaf or:origin='intended'>foo</leaf>
in case the intended configuration datastore configured the value
'foo' (despite this value matching the default). The with-defaults
solution is pretty complex because it tries to handle how different
systems deal with configuration defaults. The idea is to not carry
this complexity over to in-use values in the operational state
datastore.
Before NMDA, the client could decide if it wanted to retrieve default
nodes or not.
This client-choice has been removed from NMDA, which is a problem.
We tried to reach a sensible compromise on the data returned from
operational (defined in section 5.3 of the NMDA architecture):
- it should return explicit values for everything that is affecting
the actual running state of the device (regardless of whether the
operational value matches a schema default value).
- it does not need to, and should not, return operational values for
stuff that isn't actually in use, i.e. don't return needless and
unwanted data.
In particular, if no value is returned from a particular data node in
<operational> then, barring mgmt protocol errors, a client can assume
that any functionality associated with that data node is off (i.e. not
in use).
Some examples to illustrate the behavior:
(i) If a protocol, e.g. OSPF, is not enabled/running then <operational>
does not need to return any data for it. It would be reasonable to
return a flag to indicate that OSPF is not enabled/running.
(ii) If you have some funky widget on an interface that defaults to
being off and isn't being used then <operational> don't need to return
any data for it.
(iii) But, if you have some funky widget on an interface that defaults
to being on, then the server should return data for it. If it is
actually enabled, then it would indicate that it is on and return any
associated values with its operational state, or if it is disabled then
it should explicitly report that it is off.
(iv) I would regard that all applied configuration is "in use" by the
system, even if it matches the default value, and hence it should be
reported.
This behavior for <operational> is obviously slightly different from the
existing with-default handling that is supported for configuration
datastores. As I recall, there were a couple of reasons that we decided
to have a different behavior for <operational>:
(a) to have consistent semantics for all servers, rather than different
servers supporting different with-defaults behaviors (which makes life
harder for clients because they must cope with all variants).
(b) to remove any potential ambiguity if data isn't returned. I.e. with
the existing with-defaults semantics it is not clear to me that servers
will always return an explicit value to indicate that a particular
widget is off if the schema defines that the default it that is
enabled. If the server doesn't support a given widget at all, it is
quite plausible that it will just return no data for it. In theory
features/deviations should handle this, but those don't work so well if
different linecards have different capabilities. Hence being explicit
about stuff that is in use seems more robust.
Thanks,
Rob
/js
Andy
--
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/
<https://www.jacobs-university.de/>>
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