]> RESTCONF Extension to Support Trace Context Headers Cisco Systems
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Cisco Systems
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Deutsche Telekom AG
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All For Eco
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Operations and Management NETCONF telemetry distributed systems opentelemetry This document defines an extension to the RESTCONF protocol to support Trace Context propagation as defined by the W3C. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the NETCONF Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .
Introduction Network automation and management systems commonly consist of multiple subsystems and, together with the network devices they manage, effectively form a distributed system. Distributed tracing is a methodology implemented by tracing tools to track, analyze, and debug operations such as configuration transactions across multiple distributed systems. The W3C has defined two HTTP headers, traceparent and tracestate, in for context propagation. These headers are useful for distributed systems such as those described in Section 4 of . While the traceparent header is portable and mandatory, the tracestate header is optional and is used to carry vendor-specific data in a set of key/value pairs. According to the W3C specification, each operation is uniquely identified by a "trace-id" field and carries multiple metadata fields about the operation. Propagating this Trace Context between systems provides a coherent view of the entire operation as carried out by all involved systems. In , the NETCONF protocol extension is defined, and we reuse several of the YANG and XML objects defined in that document for RESTCONF. Please refer to that document for additional context and example applications.
Terminology 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 when, and only when, they appear in all capitals, as shown here.
RESTCONF Extensions A RESTCONF server that implements the Trace Context propagation mechanism defined in this document MUST support the Trace Context traceparent header as defined in . A RESTCONF server MAY support the Trace Context tracestate header as defined in . Note that while the W3C Trace Context specification mandates that tracing tools forwarding traces MUST propagate both traceparent and tracestate headers (Section 2.3 of ), RESTCONF servers may act as trace endpoints rather than forwarding intermediaries. Since the tracestate header carries vendor-specific opaque data, its support is intentionally made optional to accommodate implementations that do not require vendor-specific trace context propagation. When interacting with these headers, the RESTCONF server follows the specifications of section 2.3 in , therefore a RESTCONF server MAY also participate in a trace by modifying the traceparent header and the relevant vendor-specific parts of the tracestate header, for example when acting as an intermediary that contributes its own span to the distributed trace.
Error Handling It is NOT RECOMMENDED to reject an RPC because of Trace Context header values. If a server decides to reject an RPC because of Trace Context header values, the server MUST return a RESTCONF rpc-error with the following values: Additionally, the error-info tag SHOULD contain relevant details about the error. Finally, the sx:structure defined in SHOULD be present in any error message from the server.
Trace Context Header Versioning The RESTCONF protocol extension described in this document refers to the Trace Context capability. The W3C traceparent and tracestate headers include the notion of versions. It would be desirable for a RESTCONF client to be able to discover the one or multiple versions of these headers supported by a server. defines a pair YANG modules that SHOULD be included in the YANG library per of the RESTCONF server supporting the RESTCONF Trace Context extension that will refer to the headers' supported versions.
Security Considerations The traceparent and tracestate headers make it easier to track and correlate the flow of requests and their downstream effects on other systems. This information may be used by unauthorized entities to infer a map of a managed network. All advice mentioned in under Privacy Considerations and Security Considerations also applies to this document. The RESTCONF protocol has to (1) use a secure transport layer (for example, TLS and QUIC ) and (2) use mutual authentication.
IANA Considerations This document has no IANA actions.
Acknowledgments The authors would like to acknowledge the valuable implementation feedback from Per Andersson. Many thanks to Raul Rivas Felix, Alexander Stoklasa, Luca Relandini, and Erwin Vrolijk for their help with the demo integrations. The help and support from Med Boucadair, Jean Quilbeuf, and Benoît Claise have also been invaluable to this work.
References Normative References Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RESTCONF Protocol This document describes an HTTP-based protocol that provides a programmatic interface for accessing data defined in YANG, using the datastore concepts defined in the Network Configuration Protocol (NETCONF). Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. The Transport Layer Security (TLS) Protocol Version 1.3 This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations. YANG Library This document describes a YANG library that provides information about the YANG modules, datastores, and datastore schemas used by a network management server. Simple caching mechanisms are provided to allow clients to minimize retrieval of this information. This version of the YANG library supports the Network Management Datastore Architecture (NMDA) by listing all datastores supported by a network management server and the schema that is used by each of these datastores. QUIC: A UDP-Based Multiplexed and Secure Transport This document defines the core of the QUIC transport protocol. QUIC provides applications with flow-controlled streams for structured communication, low-latency connection establishment, and network path migration. QUIC includes security measures that ensure confidentiality, integrity, and availability in a range of deployment circumstances. Accompanying documents describe the integration of TLS for key negotiation, loss detection, and an exemplary congestion control algorithm. NETCONF Extension to support Trace Context propagation Cisco Systems Cisco Systems Deutsche Telekom AG All For Eco This document defines how to propagate trace context information across the Network Configuration Protocol (NETCONF), that enables distributed tracing scenarios. It is an adaption of the HTTP-based W3C specification. W3C Recommendation on Trace Context Informative References Service Models Explained The IETF has produced many modules in the YANG modeling language. The majority of these modules are used to construct data models to model devices or monolithic functions. A small number of YANG modules have been defined to model services (for example, the Layer 3 Virtual Private Network Service Model (L3SM) produced by the L3SM working group and documented in RFC 8049). This document describes service models as used within the IETF and also shows where a service model might fit into a software-defined networking architecture. Note that service models do not make any assumption of how a service is actually engineered and delivered for a customer; details of how network protocols and devices are engineered to deliver a service are captured in other modules that are not exposed through the interface between the customer and the provider.
Example RESTCONF Calls All examples from Appendix B of could be recreated in this section by adding the new header described in this document. We selected one example from that document as reference.
Successful creation of New Data Resources (from Appendix B.2.1 of ) To create a new "artist" resource within the "library" resource, a client might send the following request: If the resource is created, the server might respond as follows:
Unsuccessful creation of New Data Resources (from Appendix B.2.1 of ) specifies that a vendor MAY validate the tracestate header and that the processing rules SHOULD be followed. Example of a badly formatted tracestate header using the example (Appendix B.2.1), in which a server receives a higher traceparent version 03: In this case, the server cannot parse the traceparent header and the response would be: Note that the API call was successful, but the traceparent header is new with its trace-flags set to 0 and the tracestate header was removed.
Changes (to be deleted by RFC Editor)
From version 10 to 11
  • Grammar cleanups
From version 09 to 10
  • Updated security considerations based on the Shepherd review.
  • Added Christian Rennerskog as a co-author.
From version 08 to 09
  • Explained MAY vs. W3C MUST for tracestate (OPSDir comment).
  • Mentioned "participating in a trace" (modifying headers) (OPSDir comment).
  • Fixed RFC 2119 boilerplate spacing to match the exact BCP 14 text.
  • Updated the document date.
From version 07 to 08
  • Improved the error-handling example to show the most common scenario based on the W3C standard.
  • Updated the dates.
  • Several edits based on OpsDir comments.
  • Added security considerations for QUIC and mutual authentication.
From version 06 to 07
  • More missing edits; updated dates.
From version 05 to 06
  • More missing edits.
From version 04 to 05
  • Removed unused references and terminology.
From version 03 to 04
  • Abbreviation change.
  • "ietf-trace-contex:trace-context-error-info" should have been a container in the example.
From version 02 to 03
  • Added abbreviations to the terminology.
  • Error messages are SHOULD to align with W3C handling.
  • Adapted the example to YANG module changes in the reference.
From version 01 to 02
  • Added WGLC comments.
  • Changed namespaces and module name.
  • Fixed an error in the error response.
  • Comments from Med Boucadair.
  • Removed markdown formatting of tracestate and traceparent, as the toolchain could not handle it properly.
  • Removed references to RFC 8341 (NACM), as the passage in the security considerations no longer needed it.
  • Rearranged the text in the introduction to include references in a more natural order.
  • Removed several references to "we" and replaced them with more neutral language.
  • Clarified that everything described as MUST requirements in this document applies only to RESTCONF implementations that support this document; other RESTCONF implementations do not need to care about it, as it is an optional extension.
  • Clarified that the YANG modules used by this document are defined by the sibling NETCONF document.
  • Lots of updated wording based on review feedback.
From version 00 to -01
  • Added Security Considerations.
  • Added Acknowledgments.
  • Added several normative references.
  • Added links to the latest document on GitHub.
  • Added a RESTCONF example for success and error.
  • Modified Error Handling to reflect better W3C alignment based on implementation feedback
  • Firmed up error handling and YANG-library to MUST-requirements
From version 00 to draft-ietf-netconf-restconf-trace-ctx-headers-00
  • Adopted by NETCONF WG
  • Moved repository to NETCONF WG
  • Changed build system to use martinthomson's excellent framework
  • Ran make fix-lint to remove white space at EOL etc.
  • Added this change note. No other content changes