On 12/11/2017 12:16 PM, Robert Wilton wrote:
Hi Vladimir,
On 09/12/2017 11:49, Vladimir Vassilev wrote:
On 12/08/2017 07:01 PM, Andy Bierman wrote:
Hi,
A library per datastore sounds too complicated.
I am not proposing that.
I'm slightly lost, because I thought that was exactly what you were
proposing! ;-)
I propose a solution that keeps ietf-yang-library a data model of a single
YANG context specification doing the datastore specific modeling in
ietf-datastores model instead. The solution can be both flexible
(independent yang-library data instances per datastore as my example was
focused on) or constrained ('not-implemented-in' modules leaf-list). Here is
everything that is needed:
module: ietf-datastores
+--ro datastores-state
+--ro datastore* [name]
+--ro (model)?
+--:(same-as-operational)
+--:(constrained-to-operational)
| +--ro not-implemented-in* ->
/yanglib:module-state/module/name
+--:(unconstrained)
+--ro yang-library-datastore? identityref
YANG:
...
container datastores-state {
config false;
list datastore {
key name;
}
choice model {
case same-as-operational {
}
case constrained-to-operational {
leaf-list not-implemented-in {
type leafref {
path "/yanglib:module-state/yanglib:module/yanglib:name";
}
}
}
case unconstrained {
leaf yang-library-datastore {
type identityref {
base ds:datastore;
}
}
}
}
}
...
IMO ietf-yang-library as defined in rfc7895 is modular and reusable. I do
not see why this has to be compromised.
The fundamental point proposed is that the datastore relevant bits
are kept in the ietf-datastores module instead of merging everything
in a new ietf-yang-library entangled monster module. If needed
ietf-datastores can augment ietf-yang-library but ietf-yang-library
should be usable on its own without ietf-datastores. The solution is
coherent and modular and addresses the problem statement.
The issue with this is that datastore augmentations to YANG library
would end up changing the meaning of the existing YANG library nodes.
E.g. an old client that ignores the datastore augmentations is going to
get a nasty surprise when the server does not behave how it expects.
E.g. because the configuration node that it thinks should be there isn't
there because it only supported in <operational>.
This was one of the reasons for changing YANG library.
A well written client that finds out unsupported newer versions of
ietf-yang-library (which is reported in the capabilities) or any of the NMDA
modules is deployed should not do any damage. How exactly did you solve the
problem for the bad clients by changing the structure of yang-library in a
incompatible way is something I do not understand.
In terms of the idea of just re-using YANG library but export a separate
copy for each datastore I think that this has its own problems:
- I don't like the idea of returning meta-data along with configuration
for a <get-data> on any of the configuration datastores.
There is no meta data. The datastores contain only the config false;
/modules-state tree. I think I explained that very clearly.
- How does a client know whether the YANG library for <running> applies
to the whole server (as it does today) vs just applies to the <running>
datastore (as it would for an NMDA server)?
All datastore models are "case same-as-operational" for such systems.
- It requires more handshaking between the client and server to get the
schema, since a separate request would be required for each datastore
that is supported.
Correct. Flexibility and modularity come at a price. IMO modularity is more
important in this case. And there are solutions for the problem e.g. send
all <get-data> requests before waiting for replies. NETCONF supports this.
So, for me, I think that the only way that this solution works, would be
to define a new <get-server-metadata> RPC, but even then I think that it
would make sense to combine the data together into a new YANG library
structure.
As I said my focus is on keeping ietf-yang-library modular (single YANG
model context). <get-server-metadata> or just adding datastore identities
allowing the client to use <get-data> to achieve the retrieval of the data
is of little importance to me.
At the end of the day, I don't think that a new YANG library is going to
be were the real cost for supporting NMDA comes from. I think that the
real work is supporting <operational> independently from <running> both
in the client and servers. But I also think that once servers start
implementing this properly that it will simplify automation, because
rather than a client having to guess what state a server is in, it can
actually querey, or be notified of it, without having to write a lot of
model specific code.
+1
Vladimir
Thanks,
Rob
I prefer the proposal that was made at the IETF meeting that had
a 'not-implemented-in' leaf-list and a single module list.
This constraint is already specified in the text of the revised
datastores draft. Clients conforming to the draft can expect servers
to comply with the MUST requirement even if there is a separate
yang-library data tree for each datastore the constraint of
configuration stores mapping to 'operational' should be enforced
according to the draft. There is no contradiction here.
That said I would be also be OK with ietf-datastores augmenting
ietf-yang-library with such a leaf-list ('not-implemented-in'
leaf-list) as a more constrained flavor of the same approach instead
of going for independent copies of yang-library data. For any of
that to happen change in ietf-datastores.yang is needed and change
in the original rfc7895 ietf-yang-library is not needed at all.
Vladimir
Why is it interesting to have a separate module list for regular
modules and imported modules?
I prefer to keep the conformance leaf and not change the module list.
NMDA needs to be possible to implement with a single schema tree
such that a module
is implemented in all datastores, or a subset of all
datastores. Otherwise it probably won't
get supported in clients.
Andy
On Fri, Dec 8, 2017 at 9:21 AM, Kent Watsen <kwat...@juniper.net
<mailto:kwat...@juniper.net>> wrote:
CC-ing NETCONF, where the draft is being worked on.
Kent
On Fri, 2017-12-08 at 16:34 +0100, Juergen Schoenwaelder wrote:
> On Fri, Dec 08, 2017 at 04:19:28PM +0100, Vladimir
Vassilev wrote:
> >
> > Yes. The default value for yang-library-datastore leaf is
ds:operational
> > (the only possible one for the ds:operational datastore). This
is backward
> > compatible. If one needs different model for 'running', etc.
then a new
> > datastore identity has to be defined and set in place of the
default value.
> > Then this identity can be used to read the yang-library
data with
> > <get-data>.
> >
>
> Sorry, but I have to ask this: How do I obtain the schema for the
> datastore (lets call it <running-library>) that reports the
schema for
> <running>? Is there another <running-library-library> datastore?
Will
> the recursion end? Perhaps it does since
<running-library-library>
> might have itself listed as the schema defining datastore.
I guess
> Lada will like these kind of meta and meta-meta datastores.
Not really. Metadata needn't be in datastores.
Lada
>
> /js
>
--
Ladislav Lhotka
Head, CZ.NIC Labs
PGP Key ID: 0xB8F92B08A9F76C67
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