]> RESTCONF Extension to Support Trace Context Headers Cisco Systems
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Deutsche Telekom AG
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Cisco Systems
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Operations and Management NETCONF telemetry distributed systems opentelemetry This document defines an extension to the RESTCONF protocol in order 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 sub-systems and, together with the network devices they manage, they 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 that are useful for distributed systems like the ones defined in section 4 of . 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 will re-use 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 SHOULD support the Trace Context tracestate header as defined in .
Error Handling A RESTCONF server SHOULD follow the "Processing Model for Working with Trace Context" as specified in . Based on this processing model, it is NOT RECOMMENDED to reject an RPC because of the Trace Context header values. If a server decides to reject an RPC because of the Trace Context header values, the server MUST return a RESTCONF rpc-error with the following values: Additionally, the error-info tag SHOULD contain a 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. Future updates of this document could include additional YANG modules for new headers' versions.
Security Considerations The related document defines two YANG modules that are used when implementing the Trace Context concept, regardless of YANG-based protocol. These modules are completely empty, and therefore have very limited security considerations. Their purpose is only to indicate which Trace Context header versions the server supports using YANG Library . The traceparent and tracestate headers make it easier to track and correlate the flow of requests and their downstream effect on other systems. This is indeed the whole point with these headers. This knowledge may be used by unauthorized entities to infer a map of a managed network. All advice mentioned in the under the Privacy Considerations and Security Considerations also apply to this document. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS .
IANA Considerations This document has no IANA actions.
Acknowledgments The authors would like to acknowledge the valuable implementation feedback from Christian Rennerskog and Per Andersson. Many thanks to Raul Rivas Felix, Alexander Stoklasa, Luca Relandini and Erwin Vrolijk for their help with the demos regarding integrations. The help and support from Med Boucadair, Jean Quilbeuf and Benoît Claise has 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. NETCONF Extension to support Trace Context propagation Cisco Systems Deutsche Telekom AG Cisco Systems 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 invalid headers may be discarded. Section 2.1 on Error handling, states that servers may return an error. Let's assume that an implementation follows that behavior. Example of a badly formated tracestate header using example (Appendix B.2.1), in which a server receives the following: To which the server responds with an error message:
Changes (to be deleted by RFC Editor)
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 example
From version 02 to 03
  • Added abbreviations to terminology
  • error messages are SHOULD to align with W3C handling.
  • Addapted example to YANG module changes in reference.
From version 01 to 02
  • Added WGLC comments
  • Changed namespaces and module name
  • Fix error in error response
  • Comments from Med Boucadair
  • Removed markdown formatting of tracestate and traceparent, as toolchain could not handle this properly
  • Removed references to RFC8341 (NACM) as the passage in the security considerations no longer need it
  • Rearranged text in introduction to include referenes in a more natural order
  • Removed several references to "we" and replaced with more neutral language
  • Clarified that everything described as MUST requirements in this document only apply to RESTCONF implementations that implement this document. Other RESTCONF implementations do not need to care about this document, it's an optional extension
  • Clarified that the YANG modules used by this document is defined by the sibling document for NETCONF
  • Lots of updated wording based on review feedback
From version 00 to -01
  • Added Security considerations
  • Added Acknowledgements
  • Added several Normative references
  • Added links to latest document on github
  • Added 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