ALTO Working Group Y. Yang Internet-Draft Yale University Intended status: Standards Track July 12, 2021 Expires: January 13, 2022 ALTO Transport using HTTP/2 draft-yang-alto-http2-transport-00 Abstract The ALTO base protocol and ALTO/SSE are based on HTTP/1.x, and they introduce complexities to address limitations of HTTP/1.x. The deployment of HTTP/2 allows this document to design ALTO/H2, which benefits from the additional capabilities of HTTP/2 to provide services for ALTO. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119][RFC8174] when, and only when, they appear in all capitals, as shown here. 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 January 13, 2022. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. Yang Expires January 13, 2022 [Page 1] Internet-Draft ALTO Transport Using HTTP/2 July 2021 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 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. ALTO/H2 Design Overview . . . . . . . . . . . . . . . . . . . 3 3. ALTO/H2 Information Resource Directory (IRD) . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . 7 5. ALTO based on HTTP/3 Considerations . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction Application-Layer Traffic Optimization (ALTO) provides a means for network applications to obtain network status information. The ALTO base protocol [RFC7285] is based on the sequential request and response model of HTTP/1.1 [RFC7230]; hence, in the base protocol, an ALTO client only can issue a sequence of requests on network information resources, and the ALTO server sends the information resources one-by-one, in the order of the request sequence. To address the use cases where an ALTO client may need to efficiently monitor changes to a set of network information resources and the protocol is still based on the HTTP/1.1 model, the ALTO Working Group introduces ALTO/SSE (ALTO Incremental Update based on Server-Sent- Event) [RFC8895], so that an ALTO client can manage (i.e., add and remove) a set of requests maintained at an ALTO server, and the server can continuously, concurrently, and incrementally push updates whenever a monitored network information resource changes. ALTO/SSE can be considered a more general protocol of the ALTO base protocol to transport network information. Figure 1. shows the architecture and message flow of ALTO/SSE. Yang Expires January 13, 2022 [Page 2] Internet-Draft ALTO Transport Using HTTP/2 July 2021 ------------------------------------------------------------------ | | | +-------+ +-------+ 1. init request +------+ | | | | | | <------------- | | | | | | | | -------------> | | | | 3.add/ | | | | 1'. control uri | | | | remove | | | | | | | | resource |Stream | |Update | | | | -------->|Control| private |Stream | 2a. data update |Client| -- |Server |<------->|Server | messages | | -------- | | | | --------------> | | <- | response | | | | --------------> | | | | | | | | 2b.control update| | | | +-------+ +-------+ messages +------+ | | | ------------------------------------------------------------------ Figure 1: ALTO SSE Architecture and Message Flow. With the wide deployment of newer HTTP (e.g., HTTP/2 [RFC7540]), this document specifies ALTO transport based on HTTP/2, referred to as ALTO/H2. The newer transport can provide multiple benefits: o ALTO based on HTTP/2 natively supports multiple concurrent requests pending at the server, realizing a main design goal of ALTO SSE. At the same time, instead of using two TCP connections (a control channel and a data channel) as ALTO/SSE does, ALTO based on HTTP/2 can use a single TCP connection, achieving a design with only one connection. o ALTO based on HTTP/2 can take advantage of the benefit provided by HTTP/2 to avoid head-of-line blocking in the data channel, reducing latency. o ALTO based on HTTP/2 can take advantage of other benefits of HTTP/2, including potentially higher encoding efficiency and stronger enforcement of security (i.e., using https). 2. ALTO/H2 Design Overview There are multiple design points. o First, how to transport incremental update messages to a monitored resource (e.g., in a single HTTP/2 stream or each update uses a unique HTTP/2 stream)? Since there is sequential dependency among the incremental updates to a single information resource, there is no concurrency gain in separating them into different streams. Yang Expires January 13, 2022 [Page 3] Internet-Draft ALTO Transport Using HTTP/2 July 2021 Creating multiple streams, on the other hand, has overhead. Hence, ALTO/H2 uses a single HTTP/2 stream to carry the incremental updates to each monitored request. An implication of the preceding design is that to allow flexibility, ALTO/SSE allows different types of incremental update encodings (e.g., merge patch vs JSON patch), and hence ALTO/H2 needs to solve the same problem: it needs a header layer above HTTP/2 to indicate the media type of each incremental update. o Second, how to distinguish between an ALTO service that sends a one-shot response and one that sends incremental updates. Instead of introducing ALTO/H2 to completely replace the ALTO base protocol [RFC7285] and ALTO/SSE [RFC8895], ALTO/H2 can run in parallel with them, to support incremental deployment. A single ALTO server can provide multiple resources in its IRD, and an ALTO/H2 resource is indicated in the ALTO IRD, consistent with ALTO base protocol and ALTO/SSE. 3. ALTO/H2 Information Resource Directory (IRD) Extending the IRD example in Section 8.1 of [RFC8895], Figure 2 is the IRD of an ALTO server supporting ALTO base protocol, ALTO/SSE, and ALTO/H2. In particular, "my-network-map": { "uri": "https://alto.example.com/networkmap", "media-type": "application/alto-networkmap+json", }, "my-routingcost-map": { "uri": "https://alto.example.com/costmap/routingcost", "media-type": "application/alto-costmap+json", "uses": ["my-networkmap"], "capabilities": { "cost-type-names": ["num-routingcost"] } }, "my-hopcount-map": { "uri": "https://alto.example.com/costmap/hopcount", "media-type": "application/alto-costmap+json", "uses": ["my-networkmap"], "capabilities": { "cost-type-names": ["num-hopcount"] } }, "my-filtered-cost-map": { "uri": "https://alto.example.com/costmap/filtered/constraints", Yang Expires January 13, 2022 [Page 4] Internet-Draft ALTO Transport Using HTTP/2 July 2021 "media-type": "application/alto-costmap+json", "accepts": "application/alto-costmapfilter+json", "uses": ["my-networkmap"], "capabilities": { "cost-type-names": ["num-routingcost", "num-hopcount"], "cost-constraints": true } }, "my-simple-filtered-cost-map": { "uri": "https://alto.example.com/costmap/filtered/simple", "media-type": "application/alto-costmap+json", "accepts": "application/alto-costmapfilter+json", "uses": ["my-networkmap"], "capabilities": { "cost-type-names": ["num-routingcost", "num-hopcount"], "cost-constraints": false } }, "my-props": { "uri": "https://alto.example.com/properties", "media-type": "application/alto-endpointprops+json", "accepts": "application/alto-endpointpropparams+json", "capabilities": { "prop-types": ["priv:ietf-bandwidth"] } }, "my-pv": { "uri": "https://alto.example.com/endpointcost/pv", "media-type": "multipart/related; type=application/alto-endpointcost+json", "accepts": "application/alto-endpointcostparams+json", "capabilities": { "cost-type-names": [ "path-vector" ], "ane-properties": [ "maxresbw", "persistent-entities" ] } }, "update-my-costs": { "uri": "https://alto.example.com/updates/costs", "media-type": "text/event-stream", "accepts": "application/alto-updatestreamparams+json", "uses": [ "my-network-map", "my-routingcost-map", "my-hopcount-map", "my-simple-filtered-cost-map" ], "capabilities": { "incremental-change-media-types": { Yang Expires January 13, 2022 [Page 5] Internet-Draft ALTO Transport Using HTTP/2 July 2021 "my-network-map": "application/json-patch+json", "my-routingcost-map": "application/merge-patch+json", "my-hopcount-map": "application/merge-patch+json" }, "support-stream-control": true } }, "update-my-costs-h2": { "uri": "https://alto.example.com/updates-h2/costs", "media-type": "application/alto-h2", "accepts": "application/alto-updatestreamparams+json", "uses": [ "my-network-map", "my-routingcost-map", "my-hopcount-map", "my-simple-filtered-cost-map" ], "capabilities": { "incremental-change-media-types": { "my-network-map": "application/json-patch+json", "my-routingcost-map": "application/merge-patch+json", "my-hopcount-map": "application/merge-patch+json" }, "support-stream-control": true } }, "update-my-props": { "uri": "https://alto.example.com/updates/properties", "media-type": "text/event-stream", "uses": [ "my-props" ], "accepts": "application/alto-updatestreamparams+json", "capabilities": { "incremental-change-media-types": { "my-props": "application/merge-patch+json" }, "support-stream-control": true } }, "update-my-pv": { "uri": "https://alto.example.com/updates/pv", "media-type": "text/event-stream", "uses": [ "my-pv" ], "accepts": "application/alto-updatestreamparams+json", "capabilities": { "incremental-change-media-types": { "my-pv": "application/merge-patch+json" }, Yang Expires January 13, 2022 [Page 6] Internet-Draft ALTO Transport Using HTTP/2 July 2021 "support-stream-control": true } } Note that it is straightforward for an ALTO sever to run HTTP/2 and support concurrent retrieval of multiple resources such as "my- network-map" and "my-routingcost-map" using multiple HTTP/2 streams with the need to introducing ALTO/H2. The resource "update-my-costs-h2" provides an ALTO/H2 based connection, and this is indicated by the media-type "application/ alto-h2". For an ALTO/H2 connection, the client can send in a sequence of control requests using media type application/alto- updatestreamparams+json. The server creates HTTP/2 streams and pushes updates to the client. 4. Security Considerations The properties defined in this document present no security considerations beyond those in Section 15 of the base ALTO specification [RFC7285]. 5. ALTO based on HTTP/3 Considerations One consideration of the ALTO/H2 design is the pending deployment of HTTP3. 6. IANA Considerations IANA will need to register the alto-h2 media type under ALTO registry as defined in [RFC7285]. 7. Acknowledgments The authors of this document would also like to thank many for the reviews and comments. 8. References 8.1. 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, . Yang Expires January 13, 2022 [Page 7] Internet-Draft ALTO Transport Using HTTP/2 July 2021 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014, . [RFC7285] Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S., Previdi, S., Roome, W., Shalunov, S., and R. Woundy, "Application-Layer Traffic Optimization (ALTO) Protocol", RFC 7285, DOI 10.17487/RFC7285, September 2014, . [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI 10.17487/RFC7540, May 2015, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8895] Roome, W. and Y. Yang, "Application-Layer Traffic Optimization (ALTO) Incremental Updates Using Server-Sent Events (SSE)", RFC 8895, DOI 10.17487/RFC8895, November 2020, . 8.2. Informative References [RFC7971] Stiemerling, M., Kiesel, S., Scharf, M., Seidel, H., and S. Previdi, "Application-Layer Traffic Optimization (ALTO) Deployment Considerations", RFC 7971, DOI 10.17487/ RFC7971, October 2016, . Author's Address Y. Richard Yang Yale University 51 Prospect St New Haven, CT 06520 USA Email: yry@cs.yale.edu Yang Expires January 13, 2022 [Page 8]