Network Working Group R. Wilton, Ed.
Internet-Draft Cisco Systems, Inc.
Intended status: Informational 1 November 2020
Expires: 5 May 2021
YANG Versioning Solution Overview
draft-ietf-netmod-yang-solutions-01
Abstract
This document gives an overview of the different documents that
comprise a full solution to the YANG versioning requirements
document. The purpose of this document is to help readers understand
how the discrete parts of the YANG versioning solution fit together
during working group development of the solution documents.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Solution Documents . . . . . . . . . . . . . . . . . . . . . 3
2.1. Updated YANG Module Revision Handling . . . . . . . . . . 3
2.2. YANG Semantic Versioning . . . . . . . . . . . . . . . . 4
2.3. Versioned YANG packages . . . . . . . . . . . . . . . . . 4
2.4. Dynamic YANG schema selection . . . . . . . . . . . . . . 5
2.5. YANG Schema Comparison . . . . . . . . . . . . . . . . . 6
3. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
[I-D.ietf-netmod-yang-versioning-reqs] documents the requirements for
any solution to the YANG [RFC7950] versioning problem. In
particular, chapter 5 lists the formal requirements that a solution
requires.
The complete solution to all of the YANG versioning requirements is
comprised of five documents, each addressing different aspects of the
solution. These documents are:
1. [I-D.ietf-netmod-yang-module-versioning]
2. [I-D.ietf-netmod-yang-semver]
3. [I-D.ietf-netmod-yang-packages]
4. [I-D.ietf-netmod-yang-ver-selection]
5. [I-D.ietf-netmod-yang-schema-comparison]
The aim of this document is to help readers understand how these
different solution documents fit together, and also which documents
contribute solutions that address particular individual requirements.
Open issues, across all of the solution documents are tracked at
https://github.com/netmod-wg/yang-ver-dt/issues.
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2. Solution Documents
2.1. Updated YANG Module Revision Handling
In summary, [I-D.ietf-netmod-yang-module-versioning] specifies
minimal extensions and updates to the YANG language, YANG Library,
and YANG author guidelines to provide more flexible YANG module
revision handling. The intent is that these changes and extensions
could be folded into future revisions of the updated specifications.
The document provides a base solution for all requirements except Req
2.2, Req 3.1 and Req 3.2.
The extensions and changes in the document can be summarized thus:
* It defines a YANG extension statement to indicate where non-
backwards-compatible changes have occurred in a module's revision
history.
* It relaxes the rules for the module revision history to allow for
a non-linear module revision history. I.e., any given module
revision may have multiple revisions directly derived from it.
* It defines a new import extension statement that restricts the
allowed module revisions that satisfy the import to only those
derived from a specified module revision.
* It defines a revision label extension statement to allow an
informative name to be associated with a particular revision date,
and to be used in import statements, YANG module filenames, and is
available in YANG library. One example of how the revision label
could be used is to associate a semantic versioning scheme to YANG
module revisions.
* It updates the YANG rules for changes between module revisions
that are allowed to be classified as backwards-compatible. In
particular, marking a node as obsolete is no longer classified as
a backwards compatible change.
* It provides updated guidance on how servers handle deprecated and
obsolete YANG nodes and augments YANG library with additional
leaves to report the server's behavior to clients.
* It provides an extension statement to allow a description
statement to be associated with a YANG status statement, providing
more information about why the status has changed.
* It defines how versioning relates to YANG instance data.
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* It refines the guidelines for updating modules, taking into
consideration that non-backwards-compatible changes are sometimes
necessary for various pragmatic reasons.
2.2. YANG Semantic Versioning
[I-D.ietf-netmod-yang-semver] defines a semantic versioning scheme,
derived from the semver.org 2.0.0 specification, that can be used in
conjunction with the revision label extension statement defined in
Section 2.1 to allow semantic version numbers to be used to manage
the revision lifecycle of YANG modules and other related YANG assets,
e.g., YANG packages. This document provides an enhanced solution for
Req 2.1, but organizations authoring modules are not obliged to use
this specific versioning scheme, and could choose a different
overlaid versioning scheme, or none at all and rely solely on
revision dates.
The aims of the YANG semantic versioning scheme are:
* to generally allow clients to determine whether NBC changes have
occurred between two revisions from the version number alone,
without having to check the full revision history;
* to give a more informative identifier for a branched revision
history over revision dates alone;
* to allow revision branches that contain fixes for published non-
latest releases.
2.3. Versioned YANG packages
The two previous solution documents primarily address version and
revision management of individual modules.
[I-D.ietf-netmod-yang-packages] provides a mechanism to group sets of
related YANG modules revisions together, into constructs called YANG
packages, and to apply a versioning scheme to the groups.
The core part of this document are YANG module definitions that
define a YANG package. The definitions are used as an augmentation
to YANG library and also in YANG instance data documents for offline
access.
The principle aims of YANG packages are:
To define an efficient hierarchical structure that can precisely
specify a YANG schema.
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To provide an simple alternative mechanism to manage conformance
of modules. Rather than checking conformance against a set of
individual YANG module revisions and enabled features, it should
be easier to check for conformance against a much smaller set of
YANG package versions.
To provide a more efficient mechanism for servers to share
conformance information with clients. Rather that downloading and
comparing all individual module revisions and features via YANG
library, the client can just check whether the package version is
compatible instead. The package definition could be retrieved and
cached from multiple sources.
To define constructs that can be used for YANG schema selection.
Although the YANG packages document does not satisfy any versioning
requirements directly, it provides foundational building blocks for
the schema selection solution, described in Section 2.4, that does
address two of the requirements.
2.4. Dynamic YANG schema selection
[I-D.ietf-netmod-yang-ver-selection] specifies a solution for
requirements 3.1 and 3.2 via the use of
[I-D.ietf-netmod-yang-packages] and a model and protocol based schema
selection scheme that can be used by clients to choose which schemas
to use when interacting with the device from the available schema
that are supported and advertised by the server.
The dynamic YANG schema selection solution:
allows servers to define named 'schema-sets' which specify the
schema for each supported datastore via references to YANG
packages;
can support clients choosing a single default schema-set (from
those advertised by the server) that is used for all NETCONF/
RESTCONF protocol sessions;
can support clients enabling multiple compatible secondary schema-
sets that can be used on separate NETCONF/RESTCONF protocol
sessions;
can support clients configuring named custom schema-sets that can
be selected as default or secondary schema-sets;
can support different module versions via placing them in
different schema-sets;
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can support different schema families (e.g., IETF YANG modules ,
native vendor, or OpenConfig);
allows considerable freedom in the schema selection capabilities
that servers choose to support.
2.5. YANG Schema Comparison
The final piece of the solution jigsaw is a document that describes
how to algorithmically compare YANG schema, addressing Req 2.2.
[I-D.ietf-netmod-yang-schema-comparison] specifies an algorithm that
can be used to compare two revisions of a YANG schema to determine
the overall scope of the changes, and a list of the specific changes,
between the two revisions.
The YANG Schema Comparison solution:
defines a algorithm for comparing two YANG schema, identifying the
differences and classifying them as backwards-compatible, non-
backwards-compatible or editorial;
can be used to compare individual YANG module revisions;
can be used to compare YANG schema defined using YANG packages;
can filter the comparison output to the subset of the schema nodes
that are of interest, providing a more precise answer for clients
to determine whether they would likely be affected when upgrading
between two schema versions;
defines YANG extensions to improve the accuracy of the comparison
algorithm by explicitly annotating the type of change to
statements within a YANG module, for use where the type of change
would otherwise be ambiguous to a simple programmatic comparison
algorithm.
3. Contributors
This document grew out of the YANG module versioning design team that
started after IETF 101. The following individuals are (or have been)
members of that design team and have contributed to defining the
problem, specifying the requirements, and working on a solution:
* Balazs Lengyel
* Benoit Claise
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* Ebben Aries
* Jason Sterne
* Joe Clarke
* Juergen Schoenwaelder
* Mahesh Jethanandani
* Michael (Wangzitao)
* Qin Wu
* Reshad Rahman
* Rob Wilton
* Susan Hares
* Wu Bo
4. Security Considerations
The document does not define any new protocol or data model. There
is no security impact.
5. IANA Considerations
None.
6. References
6.1. Normative References
[I-D.ietf-netmod-yang-versioning-reqs]
Clarke, J., "YANG Module Versioning Requirements", Work in
Progress, Internet-Draft, draft-ietf-netmod-yang-
versioning-reqs-03, 29 June 2020,
<https://tools.ietf.org/html/draft-ietf-netmod-yang-
versioning-reqs-03>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
6.2. Informative References
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[I-D.ietf-netmod-yang-module-versioning]
Wilton, R., Rahman, R., Lengyel, B., Clarke, J., Sterne,
J., Claise, B., and K. D'Souza, "Updated YANG Module
Revision Handling", Work in Progress, Internet-Draft,
draft-ietf-netmod-yang-module-versioning-01, 10 July 2020,
<https://tools.ietf.org/html/draft-ietf-netmod-yang-
module-versioning-01>.
[I-D.ietf-netmod-yang-packages]
Wilton, R., Rahman, R., Clarke, J., Sterne, J., and W. Bo,
"YANG Packages", Work in Progress, Internet-Draft, draft-
ietf-netmod-yang-packages-00, 17 March 2020,
<https://tools.ietf.org/html/draft-ietf-netmod-yang-
packages-00>.
[I-D.ietf-netmod-yang-schema-comparison]
Wilton, R., "YANG Schema Comparison", Work in Progress,
Internet-Draft, draft-ietf-netmod-yang-schema-comparison-
00, 17 March 2020, <https://tools.ietf.org/html/draft-
ietf-netmod-yang-schema-comparison-00>.
[I-D.ietf-netmod-yang-semver]
Claise, B., Clarke, J., Rahman, R., Wilton, R., Lengyel,
B., Sterne, J., and K. D'Souza, "YANG Semantic
Versioning", Work in Progress, Internet-Draft, draft-ietf-
netmod-yang-semver-01, 13 July 2020,
<https://tools.ietf.org/html/draft-ietf-netmod-yang-
semver-01>.
[I-D.ietf-netmod-yang-ver-selection]
Wilton, R., Rahman, R., Clarke, J., Sterne, J., and W. Bo,
"YANG Schema Selection", Work in Progress, Internet-Draft,
draft-ietf-netmod-yang-ver-selection-00, 17 March 2020,
<https://tools.ietf.org/html/draft-ietf-netmod-yang-ver-
selection-00>.
Author's Address
Robert Wilton (editor)
Cisco Systems, Inc.
Email: rwilton@cisco.com
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