| NETCONF | E. Voit |
| Internet-Draft | R. Rahman |
| Intended status: Standards Track | E. Nilsen-Nygaard |
| Expires: April 22, 2019 | Cisco Systems |
| A. Clemm | |
| Huawei | |
| A. Bierman | |
| YumaWorks | |
| October 19, 2018 |
Dynamic subscription to YANG Events and Datastores over RESTCONF
draft-ietf-netconf-restconf-notif-09
This document provides a RESTCONF binding to the dynamic subscription capability of both subscribed notifications and YANG-Push.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 22, 2019.
Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
Mechanisms to support event subscription and push are defined in [I-D.draft-ietf-netconf-subscribed-notifications]. Enhancements to [I-D.draft-ietf-netconf-subscribed-notifications] which enable YANG datastore subscription and push are defined in [I-D.ietf-netconf-yang-push]. This document provides a transport specification for dynamic subscriptions over RESTCONF [RFC8040]. Driving these requirements is [RFC7923].
The streaming of notifications encapsulating the resulting information push is done via the mechanism described in section 6.3 of [RFC8040].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.
The following terms use the definitions from [I-D.draft-ietf-netconf-subscribed-notifications]: dynamic subscription, event stream, notification message, publisher, receiver, subscriber, and subscription.
Other terms reused include datastore, which is defined in [RFC8342], and HTTP2 stream which maps to the definition of "stream" within [RFC7540], Section 2.
[ note to the RFC Editor - please replace XXXX within this document with the number of this document ]
This section provides specifics on how to establish and maintain dynamic subscriptions over RESTCONF [RFC8040]. Subscribing to event streams is accomplished in this way via RPCs defined within [I-D.draft-ietf-netconf-subscribed-notifications] Section 2.4, the RPCs are done via RESTCONF POSTs. YANG datastore subscription is accomplished via augmentations to [I-D.draft-ietf-netconf-subscribed-notifications] as described within [I-D.ietf-netconf-yang-push] Section 4.4.
As described in [RFC8040] Section 6.3, a GET needs to be made against a specific URI on the publisher. Subscribers cannot pre-determine the URI against which a subscription might exist on a publisher, as the URI will only exist after the "establish-subscription" RPC has been accepted. Therefore, the POST for the "establish-subscription" RPC replaces the GET request for the "location" leaf which is used in [RFC8040] to obtain the URI. The subscription URI will be determined and sent as part of the response to the "establish-subscription" RPC, and a subsequent GET to this URI will be done in order to start the flow of notification messages back to the subscriber. A subscription does not move to the active state as per Section 2.4.1. of [I-D.draft-ietf-netconf-subscribed-notifications] until the GET is received.
For a dynamic subscription, where a RESTCONF session doesn't already exist, a new RESTCONF session is initiated from the subscriber.
As stated in Section 2.1 of [RFC8040], a subscriber MUST establish the HTTP session over TLS [RFC5246] in order to secure the content in transit.
Without the involvement of additional protocols, HTTP sessions by themselves do not allow for a quick recognition of when the communication path has been lost with the publisher. Where quick recognition of the loss of a publisher is required, a subscriber SHOULD use a TLS heartbeat [RFC6520], just from receiver to publisher, to track HTTP session continuity.
Loss of the heartbeat MUST result in any subscription related TCP sessions between those endpoints being torn down. A subscriber can then attempt to re-establish the dynamic subscription by using the procedure described in Section 3.
Subscribers can learn what event streams a RESTCONF server supports by querying the "streams" container of ietf-subscribed-notification.yang in [I-D.draft-ietf-netconf-subscribed-notifications]. Support for the "streams" container of ietf-restconf-monitoring.yang in [RFC8040] is not required.
Subscribers can learn what datastores a RESTCONF server supports by following [I-D.draft-ietf-netconf-nmda-restconf].
Specific HTTP responses codes as defined in [RFC7231] section 6 will indicate the result of RESTCONF RPC requests with publisher. An HTTP status code of 200 is the proper response to any successful RPC defined within [I-D.draft-ietf-netconf-subscribed-notifications] or [I-D.ietf-netconf-yang-push].
If a publisher fails to serve the RPC request for one of the reasons indicated in [I-D.draft-ietf-netconf-subscribed-notifications] Section 2.4.6 or [I-D.ietf-netconf-yang-push] Appendix A, this will be indicated by "406" status code transported in the HTTP response.
When a "406" status code is returned, the RPC reply MUST include an "rpc-error" element per [RFC8040] Section 7.1 with the following parameter values:
RPC select an identity with a base
---------------------- ------------------------------
establish-subscription establish-subscription-error
modify-subscription modify-subscription-error
delete-subscription delete-subscription-error
kill-subscription kill-subscription-error
resynch-subscription resynch-subscription-error
Each error identity will be inserted as the "error-app-tag" using JSON encoding following the form <modulename>:<identityname>. An example of such as valid encoding would be "ietf-subscribed-notifications:no-such-subscription".
In case of error responses to an "establish-subscription" or "modify-subscription" request there is the option of including an "error-info" node. This node may contain hints for parameter settings that might lead to successful RPC requests in the future. Following are the yang-data structures which may be returned:
establish-subscription returns hints in yang-data structure
---------------------- ------------------------------------
target: event stream establish-subscription-stream-error-info
target: datastore establish-subscription-datastore-error-info
modify-subscription returns hints in yang-data structure
---------------------- ------------------------------------
target: event stream modify-subscription-stream-error-info
target: datastore modify-subscription-datastore-error-info
The yang-data included within "error-info" SHOULD NOT include the
optional leaf "error-reason", as such a leaf would be redundant
with information that is already placed within the
"error-app-tag".
In case of an rpc error as a result of a "delete-subscription", a
"kill-subscription", or a "resynch-subscription" request, no
"error-info" needs to be included, as the "subscription-id" is
the only RPC input parameter and no hints regarding this RPC input
parameters need to be provided.
Note that "error-path" [RFC8040] does not need to be included with the "rpc-error" element, as subscription errors are generally associated with the choice of RPC input parameters.
The call flow is defined in Figure 1. The logical connections denoted by (a) and (b) can be a TCP connection or an HTTP2 stream (multiple HTTP2 streams can be carried in one TCP connection). Requests to [I-D.draft-ietf-netconf-subscribed-notifications] or [I-D.ietf-netconf-yang-push] augmented RPCs are sent on a connection indicated by (a). A successful "establish-subscription" will result in an RPC response returned with both a subscription identifier which uniquely identifies a subscription, as well as a URI which uniquely identifies the location of subscription on the publisher (b). This URI is defined via the "uri" leaf the Data Model in Section 7.
An HTTP GET is then sent on a separate logical connection (b) to the URI on the publisher. This initiates the publisher to initiate the flow of notification messages which are sent in SSE [W3C-20150203] as a response to the GET.
+--------------+ +--------------+
| Subscriber | | Publisher |
| | | |
| Logical | | Logical |
| Connection | | Connection |
| (a) (b) | | (a) (b) |
+--------------+ +--------------+
| RESTCONF POST (RPC:establish-subscription) |
|--------------------------------------------->|
| HTTP 200 OK (ID,URI)|
|<---------------------------------------------|
| |HTTP GET (URI) |
| |--------------------------------------------->|
| | HTTP 200 OK|
| |<---------------------------------------------|
| | SSE (notif-message)|
| |<---------------------------------------------|
| RESTCONF POST (RPC:modify-subscription) | |
|--------------------------------------------->| |
| | HTTP 200 OK| |
|<---------------------------------------------| |
| | SSE (subscription-modified)|
| |<------------------------------------------(c)|
| | SSE (notif-message)|
| |<---------------------------------------------|
| RESTCONF POST (RPC:delete-subscription) | |
|--------------------------------------------->| |
| | HTTP 200 OK| |
|<---------------------------------------------| |
| | |
| |
Figure 1: Dynamic with server-sent events
Additional requirements for dynamic subscriptions over SSE include:
A publisher MUST terminate a subscription in the following cases:
A publisher MAY terminate a subscription at any time as stated in [I-D.draft-ietf-netconf-subscribed-notifications] Section 1.3
To meet subscription quality of service promises, the publisher MUST take any existing subscription "dscp" and apply it to the DSCP marking in the IP header.
In addition, where HTTP2 transport is available to a notification message queued for transport to a receiver, the publisher MUST:
Notification messages transported over RESTCONF will be encoded according to [RFC8040], section 6.4.
The YANG model defined in Section 7 has one leaf augmented into four places of [I-D.draft-ietf-netconf-subscribed-notifications], plus two identities. As the resulting full tree is large, it will only be inserted at later stages of this document.
This module references [I-D.draft-ietf-netconf-subscribed-notifications].
<CODE BEGINS> file "ietf-restconf-subscribed-notifications@2018-10-19.yang"
module ietf-restconf-subscribed-notifications {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-restconf-subscribed-notifications";
prefix rsn;
import ietf-subscribed-notifications {
prefix sn;
}
import ietf-inet-types {
prefix inet;
}
organization "IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: <http:/tools.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
Editor: Eric Voit
<mailto:evoit@cisco.com>
Editor: Alexander Clemm
<mailto:ludwig@clemm.org>
Editor: Reshad Rahman
<mailto:rrahman@cisco.com>";
description
"Defines RESTCONF as a supported transport for subscribed
event notifications.
Copyright (c) 2018 IETF Trust and the persons identified as authors
of the code. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, is permitted pursuant to, and subject to the license
terms contained in, the Simplified BSD License set forth in Section
4.c of the IETF Trust's Legal Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see the RFC
itself for full legal notices.";
revision 2018-10-19 {
description
"Initial version";
reference
"RFC XXXX: RESTCONF Transport for Event Notifications";
}
grouping uri {
description
"Provides a reusable description of a URI.";
leaf uri {
type inet:uri;
config false;
description
"Location of a subscription specific URI on the publisher.";
}
}
augment "/sn:establish-subscription/sn:output" {
description
"This augmentation allows RESTCONF specific parameters for a
response to a publisher's subscription request.";
uses uri;
}
augment "/sn:subscriptions/sn:subscription" {
description
"This augmentation allows RESTCONF specific parameters to be
exposed for a subscription.";
uses uri;
}
augment "/sn:subscription-modified" {
description
"This augmentation allows RESTCONF specific parameters to be included
part of the notification that a subscription has been modified.";
uses uri;
}
}
<CODE ENDS>
This document registers the following namespace URI in the "IETF XML Registry" [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:ietf-restconf-subscribed-notifications
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.
This document registers the following YANG module in the "YANG Module Names" registry [RFC6020]:
Name: ietf-restconf-subscribed-notifications
Namespace: urn:ietf:params:xml:ns:yang:ietf-restconf-subscribed-notifications
Prefix: rsn
Reference: RFC XXXX: RESTCONF Transport for Event Notifications
The YANG module specified in this document defines a schema for data that is designed to be accessed via network management transports such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC5246].
The one new data node introduced in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control read access (e.g., via get, get-config, or notification) to this data nodes. These are the subtrees and data nodes and their sensitivity/vulnerability:
Container: "/subscriptions"
We wish to acknowledge the helpful contributions, comments, and suggestions that were received from: Ambika Prasad Tripathy, Alberto Gonzalez Prieto, Susan Hares, Tim Jenkins, Balazs Lengyel, Kent Watsen, Michael Scharf, Guangying Zheng, Martin Bjorklund and Qin Wu.
| [I-D.draft-ietf-netconf-netconf-event-notifications] | Clemm, Alexander., Voit, Eric., Gonzalez Prieto, Alberto., Nilsen-Nygaard, E. and A. Tripathy, "NETCONF support for event notifications", May 2018. |
| [I-D.draft-ietf-netconf-nmda-restconf] | Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K. and R. Wilton, "RESTCONF Extensions to Support the Network Management Datastore Architecture", April 2018. |
| [RFC7231] | Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 10.17487/RFC7231, June 2014. |
| [RFC7923] | Voit, E., Clemm, A. and A. Gonzalez Prieto, "Requirements for Subscription to YANG Datastores", RFC 7923, DOI 10.17487/RFC7923, June 2016. |
| [RFC8347] | Liu, X., Kyparlis, A., Parikh, R., Lindem, A. and M. Zhang, "A YANG Data Model for the Virtual Router Redundancy Protocol (VRRP)", RFC 8347, DOI 10.17487/RFC8347, March 2018. |
| [XPATH] | Clark, J. and S. DeRose, "XML Path Language (XPath) Version 1.0", November 1999. |
This section is non-normative. To allow easy comparison, this section mirrors the functional examples shown with NETCONF over XML within [I-D.draft-ietf-netconf-netconf-event-notifications]. In addition, HTTP2 vs HTTP1.1 headers are not shown as the contents of the JSON encoded objects are identical within.
The following figure shows two successful "establish-subscription" RPC requests as per [I-D.draft-ietf-netconf-subscribed-notifications]. The first request is given a subscription identifier of 22, the second, an identifier of 23.
+------------+ +-----------+
| Subscriber | | Publisher |
+------------+ +-----------+
| |
|establish-subscription |
|------------------------------>| (a)
| HTTP 200 OK, id#22, URI#1 |
|<------------------------------| (b)
|GET (URI#1) |
|------------------------------>| (c)
| HTTP 200 OK,notif-mesg (id#22)|
|<------------------------------|
| |
| |
|establish-subscription |
|------------------------------>|
| HTTP 200 OK, id#23, URI#2|
|<------------------------------|
|GET (URI#2) |
|------------------------------>|
| |
| |
| notif-mesg (id#22)|
|<------------------------------|
| HTTP 200 OK,notif-mesg (id#23)|
|<------------------------------|
| |
Figure 2: Multiple subscriptions over RESTCONF/HTTP
To provide examples of the information being transported, example messages for interactions in Figure 2 are detailed below:
POST /restconf/operations/ietf-subscribed-notifications:establish-subscription
{
"ietf-subscribed-notifications:input": {
"stream": "NETCONF",
"stream-xpath-filter": "/example-module:foo/",
"dscp": "10"
}
}
Figure 3: establish-subscription request (a)
As publisher was able to fully satisfy the request, the publisher sends the subscription identifier of the accepted subscription, and the URI:
HTTP status code - 200
{
"id": "22",
"uri": "https://example.com/restconf/subscriptions/22"
}
Figure 4: establish-subscription success (b)
Upon receipt of the successful response, the subscriber does a GET the provided URI to start the flow of notification messages. When the publisher receives this, the subscription is moved to the active state (c).
GET /restconf/subscriptions/22
Figure 5: establish-subscription subsequent POST
While not shown in Figure 2, if the publisher had not been able to fully satisfy the request, or subscriber has no authorization to establish the subscription, the publisher would have sent an RPC error response. For instance, if the "dscp" value of 10 asserted by the subscriber in Figure 3 proved unacceptable, the publisher may have returned:
HTTP status code - 406
{ "ietf-restconf:errors" : {
"error" : [
{
"error-type": "application",
"error-tag": "operation-failed",
"error-severity": "error",
"error-app-tag":
"ietf-subscribed-notifications:dscp-unavailable"
}
]
}
}
Figure 6: an unsuccessful establish subscription
The subscriber can use this information in future attempts to establish a subscription.
An existing subscription may be modified. The following exchange shows a negotiation of such a modification via several exchanges between a subscriber and a publisher. This negotiation consists of a failed RPC modification request/response, followed by a successful one.
+------------+ +-----------+
| Subscriber | | Publisher |
+------------+ +-----------+
| |
| notification message (id#23)|
|<-----------------------------|
| |
|modify-subscription (id#23) |
|----------------------------->| (d)
| HTTP 406 error (with hint)|
|<-----------------------------| (e)
| |
|modify-subscription (id#23) |
|----------------------------->|
| HTTP 200 OK |
|<-----------------------------|
| |
| notif-mesg (id#23)|
|<-----------------------------|
| |
Figure 7: Interaction model for successful subscription modification
If the subscription being modified in Figure 7 is a datastore subscription as per [I-D.ietf-netconf-yang-push], the modification request made in (d) may look like that shown in Figure 8. As can be seen, the modifications being attempted are the application of a new xpath filter as well as the setting of a new periodic time interval.
POST /restconf/operations/ietf-subscribed-notifications:modify-subscription
{
"ietf-subscribed-notifications:input": {
"id": "23",
"ietf-yang-push:datastore-xpath-filter": "/example-module:foo/example-module:bar",
"ietf-yang-push:periodic": {
"ietf-yang-push:period": "500"
}
}
}
Figure 8: Subscription modification request (c)
If the publisher can satisfy both changes, the publisher sends a positive result for the RPC. If the publisher cannot satisfy either of the proposed changes, the publisher sends an RPC error response (e). The following is an example RPC error response for (e) which includes a hint. This hint is an alternative time period value which might have resulted in a successful modification:
HTTP status code - 406
{ "ietf-restconf:errors" : {
"error" : [
"error-type": "application",
"error-tag": "operation-failed",
"error-severity": "error",
"error-app-tag": "ietf-yang-push:period-unsupported",
"error-info": {
"ietf-yang-push":
"modify-subscription-datastore-error-info": {
"period-hint": "3000"
}
}
]
}
}
Figure 9: Modify subscription failure with Hint (e)
The following demonstrates deleting a subscription. This subscription may have been to either a stream or a datastore.
POST /restconf/operations/ietf-subscribed-notifications:delete-subscription
{
"delete-subscription": {
"id": "22"
}
}
Figure 10: Delete subscription
If the publisher can satisfy the request, the publisher replies with success to the RPC request.
If the publisher cannot satisfy the request, the publisher sends an error-rpc element indicating the modification didn't work. Figure 11 shows a valid response for existing valid subscription identifier, but that subscription identifier was created on a different transport session:
HTTP status code - 406
{
"ietf-restconf:errors" : {
"error" : [
"error-type": "application",
"error-tag": "operation-failed",
"error-severity": "error",
"error-app-tag":
"ietf-subscribed-notifications:no-such-subscription"
]
}
}
Figure 11: Unsuccessful delete subscription
A publisher will send subscription state notifications according to the definitions within [I-D.draft-ietf-netconf-subscribed-notifications]).
A "subscription-modified" encoded in JSON would look like:
{
"ietf-restconf:notification" : {
"eventTime": "2007-09-01T10:00:00Z",
"ietf-subscribed-notifications:subscription-modified": {
"id": "39",
"uri": "https://example.com/restconf/subscriptions/22"
"stream-xpath-filter": "/example-module:foo",
"stream": {
"ietf-netconf-subscribed-notifications" : "NETCONF"
}
}
}
}
Figure 12: subscription-modified subscription state notification
A "subscription-completed" would look like:
{
"ietf-restconf:notification" : {
"eventTime": "2007-09-01T10:00:00Z",
"ietf-subscribed-notifications:subscription-completed": {
"id": "39",
}
}
}
Figure 13: subscription-completed notification in JSON
The "subscription-resumed" and "replay-complete" are virtually identical, with "subscription-completed" simply being replaced by "subscription-resumed" and "replay-complete".
A "subscription-terminated" would look like:
{
"ietf-restconf:notification" : {
"eventTime": "2007-09-01T10:00:00Z",
"ietf-subscribed-notifications:subscription-terminated": {
"id": "39",
"error-id": "suspension-timeout"
}
}
}
Figure 14: subscription-terminated subscription state notification
The "subscription-suspended" is virtually identical, with "subscription-terminated" simply being replaced by "subscription-suspended".
This section provides an example which illustrate the method of filtering event record contents. The example is based on the YANG notification "vrrp-protocol-error-event" as defined per the ietf-vrrp.yang module within [RFC8347]. Event records based on this specification which are generated by the publisher might appear as:
data: {
data: "ietf-restconf:notification" : {
data: "eventTime" : "2018-09-14T08:22:33.44Z",
data: "ietf-vrrp:vrrp-protocol-error-event" : {
data: "protocol-error-reason" : "checksum-error"
data: }
data: }
data: }
Figure 15: RFC 8347 (VRRP) - Example Notification
Suppose a subscriber wanted to establish a subscription which only passes instances of event records where there is a "checksum-error" as part of a VRRP protocol event. Also assume the publisher places such event records into the NETCONF stream. To get a continuous series of matching event records, the subscriber might request the application of an XPath filter against the NETCONF stream. An "establish-subscription" RPC to meet this objective might be:
POST /restconf/operations/ietf-subscribed-notifications:establish-subscription
{
"ietf-subscribed-notifications:input": {
"stream": "NETCONF",
"stream-xpath-filter": "/ietf-vrrp:vrrp-protocol-error-event[protocol-error-reason='checksum-error']/",
}
}
Figure 16: Establishing a subscription error reason via XPath
For more examples of XPath filters, see [XPATH].
Suppose the "establish-subscription" in Figure 16 was accepted. And suppose later a subscriber decided they wanted to broaden this subscription cover to all VRRP protocol events (i.e., not just those with a "checksum error"). The subscriber might attempt to modify the subscription in a way which replaces the XPath filter with a subtree filter which sends all VRRP protocol events to a subscriber. Such a "modify-subscription" RPC might look like:
POST /restconf/operations/ietf-subscribed-notifications:modify-subscription
{
"ietf-subscribed-notifications:input": {
"stream": "NETCONF",
"stream-subtree-filter": {
"/ietf-vrrp:vrrp-protocol-error-event" : {}
}
}
}
Figure 17
For more examples of subtree filters, see [RFC6241], section 6.4.
(To be removed by RFC editor prior to publication)
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