Re: [netmod] Question on RFC8342 + RESTCONF extension (draft-ietf-netconf-nmda-restconf)

Robert Wilton <rwilton@cisco.com> Wed, 12 December 2018 15:10 UTC

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To: "Seehofer, Markus" <Markus.Seehofer@belden.com>, "netmod@ietf.org" <netmod@ietf.org>
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From: Robert Wilton <rwilton@cisco.com>
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Subject: Re: [netmod] Question on RFC8342 + RESTCONF extension (draft-ietf-netconf-nmda-restconf)
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Hi Markus,

On 12/12/2018 14:40, Seehofer, Markus wrote:
>
> Hello Robert,
>
> *Von:*Robert Wilton [mailto:rwilton@cisco.com]
> *Gesendet:* Mittwoch, 12. Dezember 2018 11:21
> *An:* Seehofer, Markus; netmod@ietf.org
> *Betreff:* [EXTERNAL] Re: AW: [netmod] Re: Question on RFC8342 + 
> RESTCONF extension (draft-ietf-netconf-nmda-restconf)
>
> **
>
> Hi Markus,
>
> On 11/12/2018 17:21, Seehofer, Markus wrote:
>
>     Hello Robert,
>
>     comments inline below.
>
>     BR
>
>       Markus
>
>     -----Ursprüngliche Nachricht-----
>
>     Von: Robert Wilton [mailto:rwilton@cisco.com]
>
>     Gesendet: Dienstag, 11. Dezember 2018 17:06
>
>     An: Seehofer, Markus
>
>     Cc:netmod@ietf.org  <mailto:netmod@ietf.org>
>
>     Betreff: Re: [netmod] [EXTERNAL] Re: Question on RFC8342 + RESTCONF extension (draft-ietf-netconf-nmda-restconf)
>
>     Hi Seehofer,
>
>     Please see inline ...
>
>     On 11/12/2018 14:55, Seehofer, Markus wrote:
>
>         Hello Juergen,
>
>         see my comments inline below. As being quite new to the topic, going through all the old and current RFCs and drafts is quite challenging.
>
>         So please apologize for "simple" questions or ones maybe already raised.
>
>         -----Ursprüngliche Nachricht-----
>
>         Von: Juergen Schoenwaelder
>
>         [mailto:j.schoenwaelder@jacobs-university.de]
>
>         Gesendet: Dienstag, 11. Dezember 2018 15:33
>
>         An: Seehofer, Markus
>
>         Cc:netmod@ietf.org  <mailto:netmod@ietf.org>
>
>         Betreff: [EXTERNAL] Re: [netmod] Question on RFC8342 + RESTCONF
>
>         extension (draft-ietf-netconf-nmda-restconf)
>
>         On Tue, Dec 11, 2018 at 02:17:07PM +0000, Seehofer, Markus wrote:
>
>             Hello,
>
>             Reading RFC 8342 along with draft-ietf-netconf-nmda-restconf-05 I've some questions or comprehension problems with the text.
>
>             1.       RFC 8342 (NMDA)
>
>             Chapter 5.3.  The Operational State Datastore (<operational>) says:
>
>             "The operational state datastore (<operational>) is a read-only datastore ...."
>
>             Chapter 6.2. Invocation of Actions and RPCs says:
>
>             "Actions are always invoked in the context of the operational state datastore. The node for which the action is invoked MUST exist in the operational state datastore."
>
>             Chapter 3.1 inhttps://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_pdf_draft-2Dietf-2Dnetconf-2Dnmda-2Drestconf-2D05&d=DwIBAg&c=Bg5XULDZR8GiOSSWNlpkCsRePnGDkKcI6oYL9xv1MnQ&r=2XEKVYkQjmLHi2TOJp1VSzieLZVqewIpj-RxmRgPfsM&m=CDK28X8kO2wRVDla97P_WqBIhF3OAzbWSGEmTeLdxwU&s=BSyY-GBuzzDry6oIhg-mgwMAySbhJEO9Im3Z4PD_c_4&e=  says:
>
>             "YANG actions can only be invoked in {+restconf}/ds/ietf-datastores:operational."
>
>             Question: How can one invoke an action in a as read-only defined datastore? Or am I missing something?
>
>         Why do you expect that a datastore has to be writable in order to
>
>         invoke an action? RFC 7950 has the example of a ping action tied to an
>
>         interface. (You ping a remote system from that specific interface.) In
>
>         general, actions are understood as being tied to real resources and
>
>         hence to the operational datastore. (For example, you can't ping from
>
>         an interface that is configured but not physically present.)
>
>         [MSEE]: I do not expect that a datastore has to be writeable to invoke an action, but I do expect that a "read-only" datastore is not writeable and RFC 8342 says clearly operational state datastore is "read-only".
>
>     RPCs and actions don't modify the operational state datastore as such, instead they modify the properties of the underlying system, and the operational state datastore provides a read-only view onto the state of the system.  So <operational> is only being updated as a side effect of reflecting the changes to the underlying system.
>
>     This contrasts with writable configuration datastores (e.g. <candidate> or <running>), where the client can modify the configuration in those datastores directly which will then attempt to change the behavior of the system as the config is applied.
>
>     [MSEE]: I agree but I'm still stuck with the following text.
>
>                     - draft-ietf-netconf-nmda-restconf-05 says in Chapter 3.1: "YANG actions can only be invoked in {+restconf}/ds/ietf-datastores:operational" with
>
>                        "The resource {+restconf}/ds/ietf-datastores:operational refers to the operational state datastore" and "The operational state datastore (<operational>) is a read-only datastore"
>
>                     - RFC 8040 says in Chapter 3.6 " Operation resources representing YANG actions are not identified in this subtree, since they are invoked using a URI within the '{+restconf}/data' subtree" and
>
>                       "An action is invoked as: POST {+restconf}/data/<data-resource-identifier>/<action>"
>
>                     So without NMDA it was clear, invoke an action using {+restconf}/data}. With NMDA what is the correct way to trigger an action as the draft says "YANG actions can only be invoked in {+restconf}/ds/ietf-datastores:operational"?
>
> So, you invoke it on the equivalent path using the operational datastore.
>
> E.g. to take the example from RFC 8040 3.6.2, the request pre NMDA is 
> this:
>
>        POST /restconf/data/example-actions:interfaces/\
>           interface=eth0/get-last-reset-time HTTP/1.1
>        Host: example.com
>        Accept: application/yang-data+json
>
> The equivalent path on a NMDA server is this:
>
>        POST /restconf/ds/ietf-datastores:operational/\
>           example-actions:interfaces/\
>           interface=eth0/get-last-reset-time HTTP/1.1
>        Host: example.com
>        Accept: application/yang-data+json
>
> I think that your concern might be: why is it right/OK to invoke a 
> action on what is defined as a read only structure?
>
> [MSEE]:  Exactly. By just reading "The operational state datastore 
> (<operational>) is a read-only datastore ...." may be confusing. I 
> still struggle with the text.
>
RW: I guess that you can think of <operational> just being a view on to 
the underlying system state.  I.e. you are allowed to use an action to 
modify the underlying state which, as a side effect, updates 
<operational> (because it always reflects the system state), but you 
cannot write to <operational> as an attempt to update the underlying 
system state.


>
> The answer to this is that the action isn't acting on <operational>, 
> it is acting on the underlying system and has the remit to change any 
> of the system behavior.
>
> However, before the action can be processed, the system must validate 
> that the data node that it is acting on exists, and the parameters are 
> valid.  This validation is performed against the systems operational 
> state, and hence is validated against <operational>.
>
> [MSEE]: I agree, this of course makes sense as only the <operational> 
> datastore has the informations which nodes are in use and therefore 
> are available for usage.
>
> Again, considering the example above, it wouldn't make sense to get 
> the last reset time of an interface that existed in configuration, and 
> hence was present in <running>/<intended>, but was not in <operational>.
>
> [MSEE]: Yes, I agree.
>
> In future we may need actions that are validated against other 
> datastores, but when the authors were discussing this it was unclear 
> whether proper use cases for such actions exist, and hence we decided 
> that this could be deferred to future work, which would presumably 
> come along with a concrete use case.
>
> [MSEE]: OK.
>
> [MSEE]: Along with the above questions and answers/statements (thanks 
> for this) I probably still have more questions than answers from 
> reading the RFCs and drafts.
>
> -Draft draft-ietf-netconf-nmda-restconf-05 says:
> “An NMDA-compliant server MUST implement 
> {+restconf}/ds/ietf-datastores:operational.  Other datastore resources 
> MAY be implemented”.
> Does this mean a GET to {+restconf}/data} (which is still valid) 
> returns the same data as a GET to 
> {+restconf}/ds/ietf-datastores:operational if it is NMDA compliant?
>
RW: The definition of {+restconf}/data} has not changed in any way.  So, 
the contents/behavior of {+restconf}/data} should match what is 
specified by RFC 8040.

But this is tricky (because /data mixes intended configuration with 
operational state).

Hence, I wouldn't be surprised if some implementations either:
(1) don't implement /data at all, or
(2) handle DELETE/POST/PATCH/PUT operations as if the operation was made 
against {+restconf}/ds/ietf-datastores:running, handle GET requests as 
if they the operation was made against on 
{+restconf}/ds/ietf-datastores:operational.  This would be non-standard 
behavior though ....

A future version of RESTCONF, as opposed to an extension (i.e. 
draft-ietf-netconf-nmda-restconf-05), may remove support for 
{+restconf}/data}.


>
> -If such a NMDA compliant RESTCONF server has e.g. “example-jukebox” 
> implemented, are both of the following statements correct?
>
>      PATCH /restconf/data/example-jukebox:jukebox/\
>          library/artist=Foo%20Fighters/album=Wasting%20Light HTTP/1.1
>      Host: example.com
>      If-Match: "b8389233a4c"
>      Content-Type: application/yang-data+xml
>      <album xmlns="http://example.com/ns/example-jukebox">
>       <year>2011</year>
>      </album>
>
> and
>
> PATCH /restconf/ds/ietf-datastores:operational/example-jukebox:jukebox/\
>    library/artist=Foo%20Fighters/album=Wasting%20Light HTTP/1.1
> Host: example.com
> If-Match: "b8389233a4c"
> Content-Type: application/yang-data+xml
> <album xmlns="http://example.com/ns/example-jukebox">
> <year>2011</year>
> </album>
>
>         -        Draft draft-ietf-netconf-nmda-restconf-05 says:
>                   “ YANG actions can only be invoked in
>         {+restconf}/ds/ietf-datastores:operational”
>                   In such a NMDA compliant RESTCONF server, is
>         {+restconf}/operations (RFC8040 - 3.6 Operation Resource
>         )still valid? Because the above statement says “…can only…” or
>         does one have to use:
>
RW:

No, you can't PATCH against <operational>.  PATCH is not a YANG action, 
it is a RESTCONF method.

It is covered by draft-ietf-netconf-nmda-restconf-05, section 3.2:

    o  Some datastores are read-only by nature (e.g., <intended>), and
       hence any attempt to modify these datastores will fail.  A server
       MUST return a response with a "405 Method Not Allowed" status-line
       and error-tag value "operation-not-supported".


>         POST {+restconf}/ds/ietf-datastores:operational /<operation>
>         and
>         POST {+restconf}/ds/ietf-datastores:operational
>         /<data-resource-identifier>/<action>
>         on a NMDA compliant server only?
>
You can only POST against editable configuration datastores, e.g. 
<candidate>, <running>,<startup>, and only then if the server allows this.

Thanks,
Rob


>             2.       The NMDA is a huge step forward for NC and RC,
>             thanks for that. NMDA in combination with the new RESTCONF
>             extensions let one now select one of the named datastores
>
>             in RFC 8342. Reading the RFC and draft I'm still missing (or even more overlook I guess) the following. RFC 8040 Chapter 4.5 says:
>
>             "A PUT on the datastore resource is used to replace the entire
>
>             contents of the datastore...". So does this mean one can have the same behavior as in NETCONF where you can copy the "running" config to "startup" or "candidate" config to "running" if a RESTCONF server would support them? Is there any example how this would look like if it is allowed?
>
>         A PUT does not really get you there, to copy a datastore to another you want an operation on the server.
>
>         [MSEE]: Exactly this is what I want. NETCONF specifies this clearly in the RFCs with <copy-config> but how does one trigger this with RESTCONF? I had the hope with NMDA + RESTCONF extensions this would
>
>                          be possible too. Or do I still miss something?
>
>     I think that it is theoretically possible to invoke the NETCONF RPCs (e.g. the copy-config RPC defined in ietf-netconf.yang, RFC 6241) from RESTCONF (e.g. section 3.6 of RFC 8040).
>
>     Whether this is actually a good thing to do/encourage I'm not so sure.
>
>     [MSEE]: OK. But what is the preferred way for someone implementing RESTCONF on a device who would like to have the support of <candidate>, <startup>, <running> and the new ones defined in NMDA.
>
>                     How does one copy the data from <running> to e.g. <startup> using the mechanisms RESTCONF has defined in RFC 8040? From reading the RFC it seems is out of scope of RFC 8040 but is this really intended?
>
>                     Implementing ietf-netconf.yang of course could be an option.
>
> I agree that this isn't really specified.
>
> IIRC our initial focus was to effectively get parity with RFC 8040.  
> I.e. my working assumption is that <candidate> (if present) would be 
> handled automatically and similarly updates to <startup> would be 
> handled automatically. E.g. broadly equivalent to the /data resource 
> in RESTCONF.  So in essence this boils down to clients interacting 
> with /ds/ietf-datastores:running, /ds/ietf-datastores:operational and 
> /ds/ietf-datastores:intended.  No new RESTCONF operations should be 
> necessary here.
>
> I'm also not really convinced that independently controllable 
> <startup> and <candidate> is really a great idea.
>
> Given that <running> is meant to represent persistent configuration, 
> then automatically updating <startup> as a side effect of updating 
> <running> seems like the most sensible behavior.  If the desire is for 
> some ephemeral type configuration then that would be better modeled 
> via an explicit dynamic configuration datastore (e.g. a bit like what 
> I2RS were trying to do).
>
> Similarly, instead of a shared candidate datastore, there is some work 
> investigating private candidate datastores. 
> draft-lhotka-netconf-restconf-transactions-00 gives some ideas of what 
> this could look like, but further work is required.
>
> If there is a strong requirement to allow full explicit manipulation 
> of configuration datastores then I think that we should probably 
> define explicit RPCs for these operations (modeled on the NETCONF 
> ones).  Ideally, these could be defined in a protocol neutral format 
> so that they can work with any YANG based management protocols.  In 
> the interim, using the NETCONF RPCs from RESTCONF seems like a 
> reasonable stopgap measure.
>
> [MSEE]: I agree, this would be helpful.
>
> BR
> Markus
>
> Thanks,
> Rob
>
>     Thanks,
>
>     Rob
>
>             3.       Typo inhttps://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_pdf_draft-2Dietf-2Dnetconf-2Dnmda-2Drestconf-2D05&d=DwIBAg&c=Bg5XULDZR8GiOSSWNlpkCsRePnGDkKcI6oYL9xv1MnQ&r=2XEKVYkQjmLHi2TOJp1VSzieLZVqewIpj-RxmRgPfsM&m=CDK28X8kO2wRVDla97P_WqBIhF3OAzbWSGEmTeLdxwU&s=BSyY-GBuzzDry6oIhg-mgwMAySbhJEO9Im3Z4PD_c_4&e=  Chapter 3.1 "the server would implement the resource {+restconf}/ds/example- ds-ephemeral:ds-ephemeral."
>
>             There is a space in between "example-" and "ds-ephemeral:ds-ephemeral".
>
>         Lets hope we get this fixed with the help of the RFC editor.
>
>         /js
>
>         --
>
>         Juergen Schoenwaelder           Jacobs University Bremen gGmbH
>
>         Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
>
>         Fax:   +49 421 200 3103<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.jacobs-2Duniversity.de_&d=DwIBAg&c=Bg5XULDZR8GiOSSWNlpkCsRePnGDkKcI6oYL9xv1MnQ&r=2XEKVYkQjmLHi2TOJp1VSzieLZVqewIpj-RxmRgPfsM&m=CDK28X8kO2wRVDla97P_WqBIhF3OAzbWSGEmTeLdxwU&s=w38seWi6FN48OjPfJn92--emi3rEzEiDTHsKLxEnsrg&e=>  <https://urldefense.proofpoint.com/v2/url?u=https-3A__www.jacobs-2Duniversity.de_&d=DwIBAg&c=Bg5XULDZR8GiOSSWNlpkCsRePnGDkKcI6oYL9xv1MnQ&r=2XEKVYkQjmLHi2TOJp1VSzieLZVqewIpj-RxmRgPfsM&m=CDK28X8kO2wRVDla97P_WqBIhF3OAzbWSGEmTeLdxwU&s=w38seWi6FN48OjPfJn92--emi3rEzEiDTHsKLxEnsrg&e=>
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> destroy the message and kindly notify the sender by reply e-mail. It 
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