NETCONF E. Voit Internet-Draft A. Gonzalez Prieto Intended status: Standards Track A. Tripathy Expires: September 14, 2017 E. Nilsen-Nygaard Cisco Systems A. Clemm Huawei A. Bierman YumaWorks March 13, 2017 Restconf and HTTP Transport for Event Notifications draft-ietf-netconf-restconf-notif-02 Abstract This document defines Restconf, HTTP2, and HTTP1.1 bindings for the transport of Subscription requests and corresponding push updates. Being subscribed may be either Event Notifications or objects or subtress of YANG Datastores. Status of This Memo 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 http://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 September 14, 2017. Copyright Notice Copyright (c) 2017 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents Voit, et al. Expires September 14, 2017 [Page 1] Internet-Draft Restconf-Notif March 2017 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Dynamic YANG Subscription with RESTCONF control . . . . . 3 3.2. Subscription Multiplexing . . . . . . . . . . . . . . . . 6 4. Encoded Subscription and Event Notification Examples . . . . 7 4.1. Restconf Subscription and Events over HTTP1.1 . . . . . . 7 4.2. Event Notification over HTTP2 . . . . . . . . . . . . . . 12 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.1. Normative References . . . . . . . . . . . . . . . . . . 13 7.2. Informative References . . . . . . . . . . . . . . . . . 14 Appendix A. End-to-End Deployment Guidance . . . . . . . . . . . 14 A.1. Call Home . . . . . . . . . . . . . . . . . . . . . . . . 14 A.2. TLS Heartbeat . . . . . . . . . . . . . . . . . . . . . . 15 Appendix B. Issues being worked and resolved . . . . . . . . . . 15 B.1. Unresolved Issues . . . . . . . . . . . . . . . . . . . . 15 Appendix C. Changes between revisions . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 1. Introduction Mechanisms to support Event subscription and push are defined in [sn]. Enhancements to [sn] which enable YANG Datastore subscription and push are defined in [yang-push]. This document provides a transport specification for these protocols over Restconf and HTTP. Driving these requirements is [RFC7923]. The streaming of Subscription Event Notifications has synergies with HTTP2 streams. Benefits which can be realized when transporting events directly HTTP2 [RFC7540] include: o Elimination of head-of-line blocking o Weighting and proportional dequeuing of Events from different subscriptions o Explicit precedence in subscriptions so that events from one subscription must be sent before another dequeues Voit, et al. Expires September 14, 2017 [Page 2] Internet-Draft Restconf-Notif March 2017 2. Terminology 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 [RFC2119]. The following terms use the defintions from [sn]: Configured Subscription, Dynamic Subscription, Event Notification, Publisher, Receiver, Subscriber, Subscription. 3. Solution Event subscription is defined in [sn], YANG Datastore subscription is defined in [yang-push]. This section specifies transport mechanisms applicable to both. 3.1. Dynamic YANG Subscription with RESTCONF control Dynamic Subscriptions for both [sn] and its [yang-push] augmentations are configured and managed via signaling messages transported over [RFC8040]. These interactions will be accomplished via a Restconf POST into RPCs located on the Publisher. HTTP responses codes will indicate the results of the interaction with the Publisher. An HTTP status code of 200 is the proper response to a successful RPC call. The successful will result in a HTTP message with returned subscription URI on a logically separate mechanism than was used for the original Restconf POST. This mechanism is via a parallel TCP connection in the case of HTTP 1.x, or in the case of HTTP2 via a separate HTTP stream within the HTTP connection. When a being returned by the Publisher, failure will be indicated by error codes transported in payload. Once established, the resulting stream of Event Notifications are then delivered via SSE for HTTP1.1 and via HTTP Data for HTTP2. 3.1.1. Call Flow for HTTP2 Requests to [yang-push] augmented RPCs are sent on one or more HTTP2 streams indicated by (a) in Figure 2. Event Notifications related to a single subscription are pushed on a unique logical channel (b). In the case below, a newly established subscription has its events pushed over HTTP2 stream (7). Voit, et al. Expires September 14, 2017 [Page 3] Internet-Draft Restconf-Notif March 2017 +------------+ +------------+ | Subscriber | | Publisher | |HTTP2 Stream| |HTTP2 Stream| | (a) (b) | | (a) (b) | +------------+ +------------+ | Restconf POST (RPC:establish-subscription) | |--------------------------------------------->| | HTTP 200 OK (URI)| |<---------------------------------------------| | (7)HTTP POST (URI) (7) | |--------------------------------------------->| | | HTTP 200 OK| | |<---------------------------------------------| | | HTTP Data (event-notif)| | |<---------------------------------------------| | Restconf POST (RPC:modify-subscription) | | |--------------------------------------------->| | | | HTTP 200 OK| | |<---------------------------------------------| | | | HTTP Data (subscription-modified)| | |<---------------------------------------------| | | HTTP Data (event-notif)| | |<---------------------------------------------| | Restconf POST (RPC:delete-subscription) | | |--------------------------------------------->| | | | HTTP 200 OK| | |<---------------------------------------------| | | | HTTP Headers (end of stream)| | (/7)<-----------------------------------------(/7) | Figure 1: Dynamic with HTTP2 3.1.2. Call flow for HTTP1.1 Requests to [yang-push] RPCs are sent on the TCP connection indicated by (a). Event Notifications are pushed on a separate connection (b). This connection (b) will be used for all Event Notifications across all subscriptions. Voit, et al. Expires September 14, 2017 [Page 4] Internet-Draft Restconf-Notif March 2017 +--------------+ +--------------+ | Subscriber | | Publisher | |TCP connection| |TCP connection| | (a) (b) | | (a) (b) | +--------------+ +--------------+ | Restconf POST (RPC:establish-subscription) | |--------------------------------------------->| | HTTP 200 OK (URI)| |<---------------------------------------------| | |HTTP GET (URI) | | |--------------------------------------------->| | | HTTP 200 OK| | |<---------------------------------------------| | | SSE (event-notif)| | |<---------------------------------------------| | Restconf POST (RPC:modify-subscription) | | |--------------------------------------------->| | | | HTTP 200 OK| | |<---------------------------------------------| | | | SSE (subscription-modified)| | |<---------------------------------------------| | | SSE (event-notif)| | |<---------------------------------------------| | Restconf POST (RPC:delete-subscription) | | |--------------------------------------------->| | | | HTTP 200 OK| | |<---------------------------------------------| | | | | | | Figure 2: Dynamic with HTTP1.1 3.1.3. Configured Subscription over HTTP2 With a Configured Subscription, all information needed to establish a secure relationship with that Receiver is available on the Publisher. With this information, the Publisher will establish a secure transport connection with the Receiver and then begin pushing the Event Notifications to the Receiver. Since Restconf might not exist on the Receiver, it is not desirable to require that such Event Notifications be pushed with any dependency on Restconf. Nor is there value which Restconf provides on top of HTTP. Therefore in place of Restconf, a TLS secured HTTP2 Client connection must be established with an HTTP2 Server located on the Receiver. Event Notifications will then be sent as part of an extended HTTP POST to the Receiver. Voit, et al. Expires September 14, 2017 [Page 5] Internet-Draft Restconf-Notif March 2017 POST messages will be addressed to HTTP augmentation code on the Receiver capable of accepting and responding to Event Notifications. The first POST message must be a subscription-started notification. Push update notifications must not be sent until the receipt of an HTTP 200 OK for this initial notification. The 200 OK will indicate that the Receiver is ready for Event Notifications. At this point a Subscription must be allocated its own HTTP2 stream. Figure 4 depicts this message flow. +------------+ +------------+ | Receiver | | Publisher | |HTTP2 Stream| |HTTP2 Stream| | (a) (b) | | (a) (b) | +------------+ +------------+ | HTTP Post Headers, Data (sub-start, SubID)| |<---------------------------------------------| | HTTP 200 OK | |--------------------------------------------->| | | HTTP Post Headers, Data (event-notif)| | |<---------------------------------------------| | | HTTP Data (event-notif)| | |<---------------------------------------------| | | HTTP Data (sub-terminate)| | |<---------------------------------------------| | |HTTP 200 OK | | |--------------------------------------------->| Figure 3: Configured over HTTP2 As the HTTP2 transport is available to the Receiver, the Publisher should: o take any subscription-priority and copy it into the HTTP2 stream priority, and o take a subscription-dependency if it has been provided and map the HTTP2 stream for the parent subscription into the HTTP2 stream dependency. 3.2. Subscription Multiplexing It is possible that updates might be delivered in a different sequence than generated. Reasons for this might include (but are not limited to): o replay of pushed updates Voit, et al. Expires September 14, 2017 [Page 6] Internet-Draft Restconf-Notif March 2017 o temporary loss of transport connectivity, with update buffering and different dequeuing priorities per Subscription o population, marshalling and bundling of independent Subscription Updates, and Therefore each Event Notification will include a timestamp to ensure that a Receiver understands the time when a that update was generated. Use of this timestamp can give an indication of the state of objects at a Publisher when state-entangled information is received across different subscriptions. The use of the latest Event Notification timestamp for a particular object update can introduce errors. So when state-entangled updates have inconsistent object values and temporally close timestamps, a Receiver might consider performing a GET to validate the current state of a Publisher. 4. Encoded Subscription and Event Notification Examples Transported updates will contain context data for one or more Event Notifications. Each transported Event Notification will contain several parameters: 4.1. Restconf Subscription and Events over HTTP1.1 Subscribers can dynamically learn whether a RESTCONF server supports various types of Event or Yang datastore subscription capabilities. This is done by issuing an HTTP request OPTIONS, HEAD, or GET on the stream. Some examples building upon the Call flow for HTTP1.1 from Section 3.2.2 are: GET /restconf/data/ietf-restconf-monitoring:restconf-state/ streams/stream=yang-push HTTP/1.1 Host: example.com Accept: application/yang.data+xml If the server supports it, it may respond Voit, et al. Expires September 14, 2017 [Page 7] Internet-Draft Restconf-Notif March 2017 HTTP/1.1 200 OK Content-Type: application/yang.api+xml yang-push Yang push stream xml https://example.com/streams/yang-push-xml json https://example.com/streams/yang-push-json If the server does not support any form of subscription, it may respond HTTP/1.1 404 Not Found Date: Mon, 25 Apr 2012 11:10:30 GMT Server: example-server Subscribers can determine the URL to receive updates by sending an HTTP GET as a request for the "location" leaf with the stream list entry. The stream to use for may be selected from the Event Stream list provided in the capabilities exchange. Note that different encodings are supporting using different Event Stream locations. For example, the Subscriber might send the following request: GET /restconf/data/ietf-restconf-monitoring:restconf-state/ streams/stream=yang-push/access=xml/location HTTP/1.1 Host: example.com Accept: application/yang.data+xml The Publisher might send the following response: HTTP/1.1 200 OK Content-Type: application/yang.api+xml https://example.com/streams/yang-push-xml To subscribe and start receiving updates, the subscriber can then send an HTTP GET request for the URL returned by the Publisher in the request above. The accept header must be "text/event-stream". The Voit, et al. Expires September 14, 2017 [Page 8] Internet-Draft Restconf-Notif March 2017 Publisher uses the Server Sent Events [W3C-20150203] transport strategy to push filtered Event Notifications from the Event stream. The Publisher MUST support individual parameters within the POST request body for all the parameters of a subscription. The only exception is the encoding, which is embedded in the URI. An example of this is: // subtree filter = /foo // periodic updates, every 5 seconds POST /restconf/operations/ietf-event-notifications: establish-subscription HTTP/1.1 Host: example.com Content-Type: application/yang-data+json { "ietf-event-notifications:input" : { ?stream?: ?push-data" ?period" : 5, "xpath-filter" : ?/ex:foo[starts-with(?bar?.?some']" } } Should the publisher not support the requested subscription, it may reply: Voit, et al. Expires September 14, 2017 [Page 9] Internet-Draft Restconf-Notif March 2017 HTTP/1.1 501 Not Implemented Date: Mon, 23 Apr 2012 17:11:00 GMT Server: example-server Content-Type: application/yang.errors+xml application operation-not-supported error Xpath filters not supported with an equivalent JSON encoding representation of: HTTP/1.1 501 Not Implemented Date: Mon, 23 Apr 2012 17:11:00 GMT Server: example-server Content-Type: application/yang.errors+json { "ietf-restconf:errors": { "error": { "error-type": "protocol", "error-tag": "operation-not-supported", "error-message": "Xpath filters not supported." "error-info": { "datastore-push:supported-subscription": { "subtree-filter": [null] } } } } } The following is an example of a pushed Event Notification data for the Subscription above. It contains a subtree with root foo that contains a leaf called bar: Voit, et al. Expires September 14, 2017 [Page 10] Internet-Draft Restconf-Notif March 2017 XML encoding representation: my-sub 2015-03-09T19:14:56.233Z some_string Or with the equivalent YANG over JSON encoding representation as defined in [RFC7951]: { "ietf-restconf:notification": { "datastore-push:subscription-id": "my-sub", "eventTime": "2015-03-09T19:14:56.233Z", "datastore-push:datastore-contents": { "example-mod:foo": { "bar": "some_string" } } } } To modify a Subscription, the subscriber issues another POST request on the provided URI using the same subscription-id as in the original request. For example, to modify the update period to 10 seconds, the subscriber may send: POST /restconf/operations/ietf-event-notifications: modify-subscription HTTP/1.1 Host: example.com Content-Type: application/yang-data+json { "ietf-event-notifications:input" : { ?subscription-id?: 100, ?period" : 10 } } Voit, et al. Expires September 14, 2017 [Page 11] Internet-Draft Restconf-Notif March 2017 To delete a Subscription, the Subscriber issues a DELETE request on the provided URI using the same subscription-id as in the original request 4.2. Event Notification over HTTP2 The basic encoding will look as below. It will consists of a JSON representation wrapped in an HTTP2 header. HyperText Transfer Protocol 2 Stream: HEADERS, Stream ID: 5 Header: :method: POST Stream: HEADERS, Stream ID: 5 { "ietf-yangpush:notification": { "datastore-push:subscription-id": "my-sub", "eventTime": "2015-03-09T19:14:56.233Z", "datastore-push:datastore-contents": { "foo": { "bar": "some_string" } } } } 5. Security Considerations Subscriptions could be used to intentionally or accidentally overload the resources of a Publisher. For this reason, it is important that the Publisher has the ability to prioritize the establishment and push of Event Notifications where there might be resource exhaust potential. In addition, a server needs to be able to suspend existing Subscriptions when needed. When this occurs, the subscription status must be updated accordingly and the Receivers notified. A Subscription could be used to attempt retrieve information for which a Receiver has no authorized access. Therefore it is important that data pushed via a Subscription is authorized equivalently with regular data retrieval operations. Data being pushed to a Receiver needs therefore to be filtered accordingly, just like if the data were being retrieved on-demand. The Netconf Authorization Control Model [RFC6536] applies even though the transport is not NETCONF. One or more Publishers of Configured Subscriptions could be used to overwhelm a Receiver which doesn't even support Subscriptions. There are two protections here. First Event Notifications for Configured Subscriptions MUST only be transmittable over Encrypted transports. Clients which do not want pushed Event Notifications need only Voit, et al. Expires September 14, 2017 [Page 12] Internet-Draft Restconf-Notif March 2017 terminate or refuse any transport sessions from the Publisher. Second, the HTTP transport augmentation on the Receiver must send an HTTP 200 OK to a subscription started notification before the Publisher starts streaming any events. One or more Publishers could overwhelm a Receiver which is unable to control or handle the volume of Event Notifications received. In deployments where this might be a concern, HTTP2 transport such as HTTP2) should be selected. 6. Acknowledgments We wish to acknowledge the helpful contributions, comments, and suggestions that were received from: Susan Hares, Tim Jenkins, Balazs Lengyel, Kent Watsen, Michael Scharf, and Guangying Zheng. 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC6520] Seggelmann, R., Tuexen, M., and M. Williams, "Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) Heartbeat Extension", RFC 6520, DOI 10.17487/RFC6520, February 2012, . [RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration Protocol (NETCONF) Access Control Model", RFC 6536, DOI 10.17487/RFC6536, March 2012, . [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI 10.17487/RFC7540, May 2015, . [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, . Voit, et al. Expires September 14, 2017 [Page 13] Internet-Draft Restconf-Notif March 2017 [sn] Voit, E., Clemm, A., Gonzalez Prieto, A., Prasad Tripathy, A., and E. Nilsen-Nygaard, "Subscribing to Event Notifications", February 2017, . 7.2. Informative References [RFC7923] Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements for Subscription to YANG Datastores", RFC 7923, DOI 10.17487/RFC7923, June 2016, . [RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG", RFC 7951, DOI 10.17487/RFC7951, August 2016, . [RFC8071] Watsen, K., "NETCONF Call Home and RESTCONF Call Home", RFC 8071, DOI 10.17487/RFC8071, February 2017, . [W3C-20150203] "Server-Sent Events, World Wide Web Consortium CR CR- eventsource-20121211", February 2015, . [yang-push] Clemm, A., Voit, E., Gonzalez Prieto, A., Prasad Tripathy, A., Nilsen-Nygaard, E., Bierman, A., and B. Lengyel, "Subscribing to YANG datastore push updates", March 2017, . Appendix A. End-to-End Deployment Guidance Several technologies are expected to be seen within a deployment to achieve security and ease-of-use requirements. These are not necessary for an implementation of this specification, but will be useful to consider when considering the operational context. A.1. Call Home Pub/Sub implementations should have the ability to transparently incorporate 'call home' [RFC8071] so that secure TLS connections can originate from the desired device. Voit, et al. Expires September 14, 2017 [Page 14] Internet-Draft Restconf-Notif March 2017 A.2. TLS Heartbeat HTTP sessions might not quickly allow a Subscriber to recognize when the communication path has been lost from the Publisher. To recognize this, it is possible for a Receiver to establish a TLS heartbeat [RFC6520]. In the case where a TLS heartbeat is included, it should be sent just from Receiver to Publisher. Loss of the heartbeat should result in any Subscription related TCP sessions between those endpoints being torn down. The subscription can then attempt to re-establish. Appendix B. Issues being worked and resolved (To be removed by RFC editor prior to publication) B.1. Unresolved Issues GRPC compatibility 1: Mechanisms for HTTP2 to GRPC mapping need to be considered. There is a good start there as this draft only uses POST, not GET. As GET is used in RESTCONF for capabilities discovery, we have some backwards compatibility issues with existing IETF drafts. Possible options to address are (1) provide a POST method for anything done by GET in RESTCONF, (2) await support of GET by GRPC, or (3) tunnel RESTCONF's GET messages within a GRPC POST. GRPC compatibility 2: We need to expose a method against which POST is done as events begin on a stream. See Stream 7 in figure 2. Can only send traffic to a method, not a URI. URI points to a method, not a resource. Need to add into document examples of Event streams. Document only includes yang-push examples at this point. We need to reference the viable encodings of notifications. Appendix C. Changes between revisions (To be removed by RFC editor prior to publication) v01 - v02 o Removed sections now redundant with [sn] and [yang-push] such as: mechanisms for subscription maintenance, terminology definitions, stream discovery. o 3rd party subscriptions are out-of-scope. o SSE only used with Restconf and HTTP1.1 Dynamic Subscriptions Voit, et al. Expires September 14, 2017 [Page 15] Internet-Draft Restconf-Notif March 2017 o Timeframes for event tagging are self-defined. o Clean-up of wording, references to terminology, section numbers. v00 - v01 o Removed the ability for more than one subscription to go to a single HTTP2 stream. o Updated call flows. Extensively. o SSE only used with Restconf and HTTP1.1 Dynamic Subscriptions o HTTP is not used to determine that a Receiver has gone silent and is not Receiving Event Notifications o Many clean-ups of wording and terminology Authors' Addresses Eric Voit Cisco Systems Email: evoit@cisco.com Alberto Gonzalez Prieto Cisco Systems Email: albertgo@cisco.com Ambika Prasad Tripathy Cisco Systems Email: ambtripa@cisco.com Einar Nilsen-Nygaard Cisco Systems Email: einarnn@cisco.com Alexander Clemm Huawei Email: ludwig@clemm.org Voit, et al. Expires September 14, 2017 [Page 16] Internet-Draft Restconf-Notif March 2017 Andy Bierman YumaWorks Email: andy@yumaworks.com Voit, et al. Expires September 14, 2017 [Page 17]