| Network Working Group | B. Claise |
| Internet-Draft | J. Clarke |
| Updates: 7950,8407,8525 (if approved) | R. Rahman |
| Intended status: Standards Track | R. Wilton, Ed. |
| Expires: September 18, 2020 | Cisco Systems, Inc. |
| B. Lengyel | |
| Ericsson | |
| J. Sterne | |
| Nokia | |
| K. D'Souza | |
| AT&T | |
| March 17, 2020 |
Updated YANG Module Revision Handling
draft-ietf-netmod-yang-module-versioning-00
This document specifies a new YANG module update procedure that can document when non-backwards-compatible changes have occurred during the evolution of a YANG module. It extends the YANG import statement with an earliest revision filter to better represent inter-module dependencies. It provides help and guidelines for managing the lifecycle of YANG modules and individual schema nodes. This document updates RFC 7950, RFC 8407 and RFC 8525.
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 https://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 18, 2020.
Copyright (c) 2020 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 (https://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.
This document defines a solution to the YANG module lifecycle problems described in [I-D.verdt-netmod-yang-versioning-reqs]. Complementary documents provide a complete solution to the YANG versioning requirements, with the overall relationship of the solution drafts described in [I-D.verdt-netmod-yang-solutions].
Specifically, this document recognises a need (within standards organizations, vendors, and the industry) to sometimes allow YANG modules to evolve with non-backwards-compatible changes, which could cause breakage to clients and importing YANG modules. Accepting that non-backwards-compatible changes do sometimes occur, it is important to have mechanisms to report where these changes occur, and to manage their effect on clients and the broader YANG ecosystem.
The solution comprises five parts:
Open issues are tracked at <https://github.com/netmod-wg/yang-ver-dt/issues>.
This document updates [RFC7950] section 11. Section 3 describes modifications to YANG revision handling and update rules, and Section 4 describes a YANG extension statement to do import by derived revision.
This document updates [RFC8525] section 3. Section 5 defines how a client of a YANG library datastore schema chooses which revision of an import-only module is used to resolve a module import when the definition is otherwise ambiguous.
This document updates [RFC8407] section 4.7. Section 7 provides guidelines on managing the lifecycle of YANG modules that may contain non-backwards-compatible changes and a branched revision history.
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.
In addition, this document uses the terminology:
[RFC7950] assumes, but does not explicitly state, that the revision history for a YANG module is strictly linear, i.e., it is prohibited to have two independent revisions of a YANG module that are both directly derived from the same parent revision.
This document clarifies [RFC7950] to explicitly allow non linear development of YANG module revisions, so modules MAY have multiple revisions that directly derive from the same parent revision. As per [RFC7950], YANG module revisions continue to be uniquely identified by the module's revision date, and hence all revisions of a module MUST have unique revision dates.
A module's name and revision date identifies a specific immutable definition of that module within its revision history. Hence, if a module includes submodules then the module's "include" statements MUST use "revision-date" substatements to specify the exact revision date of each included submodule.
[RFC7950] section 11 requires that all updates to a YANG module are BC to the previous revision of the module. This document allows for more flexible evolution of YANG modules: NBC changes between module revisions are allowed and are documented using a new "nbc-changes" YANG extension statement in the module revision history.
This section updates [RFC7950] section 11 to refine the rules for permissible changes when a new YANG module revision is created.
Where pragmatic, updates to YANG modules SHOULD be backwards-compatible, following the definition in Section 3.1.1.
A new module revision MAY contain NBC changes, i.e., the semantics of an existing definition MAY be changed in an NBC way without requiring a new definition with a new identifier. A new module revision with NBC changes MUST include the "rev:nbc-changes" extension substatement to signal the potential for incompatibility to existing module users and readers.
A change between two module revisions is defined as being "backwards-compatible" if the change conforms to the module update rules specified in [RFC7950] section 11, updated by the following rules:
Any changes to YANG modules that are not defined by Section 3.1.1 as being backwards-compatible are classified as "non-backwards-compatible" changes.
The "rev:nbc-changes" extension statement is used to indicate YANG module revisions that contain NBC changes.
If a revision of a YANG module contains changes, relative to the preceding revision in the revision history, that do not conform to the module update rules defined in Section 3.1.1, then a "rev:nbc-changes" extension statement MUST be added as a substatement to the "revision" statement.
Conversely, if a revision does not contain an "rev:nbc-changes" extension substatement then all changes, relative to the preceding revision in the revision history, MUST be backwards-compatible.
Each revision entry in a module or submodule MAY have a revision label associated with it, providing an alternative alias to identify a particular revision of a module or submodule. The revision label could be used to provide an additional versioning identifier associated with the revision.
YANG Semver [I-D.verdt-netmod-yang-semver] defines a versioning scheme based on Semver 2.0.0 [semver] that can be used as a revision label. All revision labels that match the pattern for the "version" typedef in the ietf-yang-semver YANG module MUST be interpreted as YANG semantic version numbers.
The revision date and revision label within a submodule's revision history have no effect on the including module's revision. Submodules MUST NOT use revision label schemes that could be confused with the including module's revision label scheme.
If a revision has an associated revision label, then it may be used instead of the revision date in two places:
The ietf-yang-revision module specifies the YANG extension statement "status-description" that can be used as a substatement of the status statement. The argument to this extension statement can contain freeform text to help readers of the module understand why the node was deprecated or made obsolete, when it is anticipated that the node will no longer be available for use, and potentially reference other schema elements that can be used instead. An example is shown below.
leaf imperial-temperature {
type int64;
units "degrees Fahrenheit";
status deprecated {
rev:status-description
"Imperial measurements are being phased out in favor
of their metric equivalents. Use metric-temperature
instead.";
}
description
"Temperature in degrees Fahrenheit.";
}
The following diagram, explanation, and module history illustrates how the branched revision history, "nbc-changes" extension statement, and "revision-label" extension statement could be used:
Example YANG module with branched revision history.
Module revision date Revision label
2019-01-01 <- 1.0.0
|
2019-02-01 <- 2.0.0
| \
2019-03-01 \ <- 3.0.0
| \
| 2019-04-01 <- 2.1.0
| |
| 2019-05-01 <- 2.2.0
|
2019-06-01 <- 3.1.0
The tree diagram above illustrates how an example module's version history might evolve, over time. For example, the tree might represent the following changes, listed in chronological order from oldest revision to newest:
Example module, revision 2019-06-01:
module example-module {
namespace "name-space";
prefix "prefix-name";
import ietf-yang-revisions { prefix "rev"; }
description
"to be completed";
revision 2019-06-01 {
rev:revision-label 3.1.0;
description "Add new functionality.";
}
revision 2019-04-01 {
rev:revision-label 3.0.0;
rev:nbc-changes;
description
"Add new functionality. Remove some deprecated nodes.";
}
revision 2019-02-01 {
rev:revision-label 2.0.0;
rev:nbc-changes;
description "Apply bugfix to pattern statement";
}
revision 2019-01-01 {
rev:revision-label 1.0.0;
description "Initial revision";
}
//YANG module definition starts here
Example module, revision 2019-05-01:
module example-module {
namespace "name-space";
prefix "prefix-name";
import ietf-yang-revisions { prefix "rev"; }
description
"to be completed";
revision 2019-05-01 {
rev:revision-label 2.2.0;
description "Backwards-compatible bugfix to enhancement.";
}
revision 2019-03-01 {
rev:revision-label 2.1.0;
description "Apply enhancement to older release train.";
}
revision 2019-02-01 {
rev:revision-label 2.0.0;
rev:nbc-changes;
description "Apply bugfix to pattern statement";
}
revision 2019-01-01 {
rev:revision-label 1.0.0;
description "Initial revision";
}
//YANG module definition starts here
RFC 7950 allows YANG module "import" statements to optionally require the imported module to have a particular revision date. In practice, importing a module with an exact revision date is often too restrictive because it requires the importing module to be updated whenever any change to the imported module occurs. The alternative choice of using an import statement without any revision date statement is also not ideal because the importing module may not work with all possible revisions of the imported module.
Instead, it is desirable for a importing module to specify a "minimum required revision" of a module that it is compatible with, based on the assumption that later revisions derived from that "minimum required revision" are also likely to be compatible. Many possible changes to a YANG module do not break importing modules, even if the changes themselves are not strictly backwards-compatible. E.g., fixing an incorrect pattern statement or description for a leaf would not break an import, changing the name of a leaf could break an import but frequently would not, but removing a container would break imports if that container is augmented by another module.
The ietf-revisions module defines the "revision-or-derived" extension statement, a substatement to the YANG "import" statement, to allow for a "minium required revision" to be specified during import:
Consider the example module "example-module" from Section 3.5 that is hypothetically available in the following revision/label pairings: 2019-01-01/1.0.0, 2019-02-01/2.0.0, 2019-03-01/3.0.0, 2019-04-01/2.1.0, 2019-05-01/2.2.0 and 2019-06-01/3.1.0. The relationship between the revisions is as before:
Module revision date Revision label
2019-01-01 <- 1.0.0
|
2019-02-01 <- 2.0.0
| \
2019-03-01 \ <- 3.0.0
| \
| 2019-04-01 <- 2.1.0
| |
| 2019-05-01 <- 2.2.0
|
2019-06-01 <- 3.1.0
This example selects module revisions that match, or are derived from the revision 2019-02-01. E.g., this dependency might be used if there was a new container added in revision 2019-02-01 that is augmented by the importing module.It includes revisions/labels: 2019-02-01/2.0.0, 2019-03-01/3.0.0, 2019-04-01/2.1.0, 2019-05-01/2.2.0 and 2019-06-01/3.1.0.
import example-module {
rev:revision-or-derived 2019-02-01;
}
Alternatively, the first example could have used the revision label "1.0.0" instead, which selects the same set of revisions/versions.
import example-module {
rev:revision-or-derived 1.0.0;
}
This example selects module revisions that are derived from 2019-04-01 by using the revision label 2.1.0. It includes revisions/labels: 2019-04-01/2.1.0 and 2019-05-01/2.2.0. Even though 2019-06-01/3.1.0 has a higher revision label version number than 2019-04-01/2.1.0 it is not a derived revision, and hence it is not a valid revision for import.
import example-module {
rev:revision-or-derived 2.1.0;
}
This example selects revisions derived from either 2019-04-01 or 2019-06-01. It includes revisions/labels: 2019-04-01/2.1.0, 2019-05-01/2.2.0, and 2019-06-01/3.1.0.
import example-module {
rev:revision-or-derived 2019-04-01;
rev:revision-or-derived 2019-06-01;
}
This document updates YANG library [RFC7895] [RFC8525] to clarify how ambiguous module imports are resolved. It also defines the YANG module, ietf-yl-revisions that augments YANG library with new versioning related meta-data.
A YANG datastore schema, defined in [RFC8525], can specify multiple revisions of a YANG module in the schema using the "import-only" list, with the requirement from [RFC7950] that only a single revision of a YANG module may be implemented.
If a YANG module import statement does not specify a specific revision within the datastore schema then it could be ambiguous as to which module revision the import statement should resolve to. Hence, a datastore schema constructed by a client using the information contained in YANG library may not exactly match the datastore schema actually used by the server.
The following two rules remove the ambiguity:
If a module import statement could resolve to more than one module revision defined in the datastore schema, and one of those revisions is implemented (i.e., not an "import-only" module), then the import statement MUST resolve to the revision of the module that is defined as being implemented by the datastore schema.
If a module import statement could resolve to more than one module revision defined in the datastore schema, and none of those revisions are implemented, then the import MUST resolve to the module revision with the latest revision date.
The "ietf-yl-revisions" YANG module has the following structure (using the notation defined in [RFC8340]):
module: ietf-yl-revisions
augment /yanglib:yang-library/yanglib:module-set/yanglib:module:
+--ro revision-label? rev:revision-label
augment /yanglib:yang-library/yanglib:schema:
+--ro deprecated-nodes-implemented? empty
+--ro obsolete-nodes-absent? empty
The ietf-yl-revisions YANG module augments the "module" list in ietf-yang-library with a "revision-label" leaf to optionally declare the revision label associated wth the particular revision of each module.
The ietf-yl-revisions YANG module augments YANG library with two leaves to allow a server to report how it handles status "deprecated" and status "obsolete" nodes. The leaves are:
Servers SHOULD set both the "deprecated-nodes-implemented" and "obsolete-nodes-absent" leaves.
If a server does not set the "deprecated-nodes-implemented" leaf, then clients MUST NOT rely solely on the "rev:nbc-changes" statements to determine whether two module revisions are backwards-compatible, and MUST also consider whether the status of any nodes has changed to "deprecated" and whether those nodes are implemented by the server.
Instance data sets [I-D.ietf-netmod-yang-instance-file-format] do not directly make use of the updated revision handling rules described in this document, as compatibility for instance data is undefined.
However, instance data specifies the content-schema of the data-set. This schema SHOULD make use of versioning using revision dates and/or revision labels for the individual YANG modules that comprise the schema or potentially for the entire schema itself (e.g., [I-D.rwilton-netmod-yang-packages] ).
In this way, the versioning of a content-schema associated with an instance data set may help a client to determine whether the instance data could also be used in conjunction with other revisions of the YANG schema, or other revisions of the modules that define the schema.
The following text updates section 4.7 of [RFC8407] to revise the guidelines for updating YANG modules.
All IETF YANG modules MUST include revision-label statements for all newly published YANG modules, and all newly published revisions of existing YANG modules. The revision-label MUST take the form of a YANG semantic version number [I-D.verdt-netmod-yang-semver].
NBC changes to YANG modules may cause problems to clients, who are consumers of YANG models, and hence YANG module authors are RECOMMENDED to minimize NBC changes and keep changes BC whenever possible.
When NBC changes are introduced, consideration should be given to the impact on clients and YANG module authors SHOULD try to mitigate that impact.
A "rev:nbc-changes" statement SHOULD be added only if there are NBC changes relative to the previous revision.
Removing old revision statements from a module's revision history could break import by revision, and hence it is RECOMMENDED to retain them. If all depencencies have been updated to not import specific revisions of a module, then the corresponding revision statements can be removed from that module. An alternative solution, if the revision section is too long, would be remove, or curtail, the older description statements associated with the previous revisions.
The "rev:revision-or-derived" extension should be used in YANG module imports to indicate revision dependencies between modules in preference to the "revision-date" statement, which causes overly strict import dependencies and SHOULD NOT be used.
A module that includes submodules MUST use the "revision-date" statement to include specific submodule revisions. Changing a module's include statements to include different submodule revisions requires a new revision of the module.
There are various valid situations where a YANG module has to be modified in an NBC way. Here are the different ways in which this can be done:
Here are some guidelines on how non-backwards-compatible changes can be made incrementally, with the assumption that deprecated nodes are implemented by the server, and obsolete nodes are not:
See Appendix A.1 for examples on how NBC changes can be made.
Guidelines for clients of modules using the new module revision update procedure:
YANG module with extension statements for annotating NBC changes, revision label, status description, and importing by version.
<CODE BEGINS> file "ietf-yang-revisions@2019-09-18.yang"
module ietf-yang-revisions {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-revisions";
prefix rev;
import ietf-yang-types {
prefix yang;
reference
"XXXX [ietf-netmod-rfc6991-bis]: Common YANG Data Types";
}
organization
"IETF NETMOD (Network Modeling) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>
Author: Benoit Claise
<mailto:bclaise@cisco.com>
Author: Joe Clarke
<mailto:jclarke@cisco.com>
Author: Reshad Rahman
<mailto:rrahman@cisco.com>
Author: Robert Wilton
<mailto:rwilton@cisco.com>
Author: Kevin D'Souza
<mailto:kd6913@att.com>
Author: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>
Author: Jason Sterne
<mailto:jason.sterne@nokia.com>";
description
"This YANG 1.1 module contains definitions and extensions to
support updated YANG revision handling.
Copyright (c) 2019 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.
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 (RFC 2119) (RFC 8174) when, and only when,
they appear in all capitals, as shown here.";
// RFC Ed.: update the date below with the date of RFC publication
// and remove this note.
// RFC Ed.: replace XXXX (inc above) with actual RFC number and
// remove this note.
revision 2019-09-18 {
description
"Initial version.";
reference
"XXXX: Updated YANG Module Revision Handling";
}
typedef revision-label {
type string {
length "1..255";
pattern '[^\s@]+';
pattern '\d{4}-\d{2}-\d{2}' {
modifier invert-match;
}
}
description
"A label associated with a YANG revision.
Excludes spaces and '@'. MUST NOT match revision-date.
Revision labels that classify as YANG semantic versions,
as defined by the ietf-yang-semver:version typedef,
MUST conform to the versioning behaviour defined in
XXXX [verdt]: YANG Semantic Versioning.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 3.3, Revision label";
}
typedef revision-date-or-label {
type union {
type yang:revision-identifier;
type revision-label;
}
description
"Represents either a YANG revision date or a revision label";
}
extension nbc-changes {
description
"This statement is used to indicate YANG module revisions that
contain non-backwards-compatible changes.
Each 'revision' statement MAY have a single 'nbc-changes'
substatement.
If a revision of a YANG module contains changes, relative to
the preceding revision in the revision history, that do not
conform to the module update rules defined in RFC-XXX, then
the 'nbc-changes' statement MUST be added as a substatement to
the revision statement.
Conversely, if a revision of a YANG module only contains
changes, relative to the preceding revision in the revision
history, that are classified as 'backwards-compatible' then
the revision statement MUST NOT contain any 'nbc-changes'
substatement.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 3.2, nbc-changes revision extension statement";
}
extension revision-label {
argument revision-label;
description
"The revision label can be used to provide an additional
versioning identifier associated with the revision. E.g., one
option for a versioning scheme that could be used is [TODO -
Reference semver draft].
The format of the revision-label argument MUST conform to the
pattern defined for the revision-label typedef.
Each 'revision' statement MAY have a single 'revision-label'
substatement.
Revision labels MUST be unique amongst all revisions of a
module.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 3.3, Revision label";
}
extension revision-or-derived {
argument revision-date-or-label;
description
"Restricts the revision of the module that may be imported to
one that matches or is derived from the specified
revision-date or revision-ñlabel.
The argument value MUST conform to the
'revision-date-or-label' defined type.
Each 'import' statement MAY have one or more
'revision-or-derived' substatements. If specified multiple
times, then any module revision that satifies at least one of
the 'revision-or-derived' statements is an acceptable revision
for import.
An 'import' statement MUST NOT contain both a
'revision-or-derived' extension statement and a
'revision-date' statement.
A particular revision of an imported module satisfies an
import's 'revision-or-derived' extension statement if the
imported module's revision history contains a revision
statement with a matching revision date or revision label.
The 'revision-or-derived' extension statement does not
gaurantee that all module revisions that satisfy an import
statement are necessarily compatible, it only gives an
indication that the revisions are more likely to be
compatible.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 4, Import by derived revision";
}
extension status-description {
argument description;
description
"Freeform text that describes why a given node has been
deprecated or made obsolete. E.g., the description could be
used to give the reason for removal, or it could point to an
alternative schema elements that can be used in lieu of the
given node.
Each 'status' statement MAY have a single 'status-description'
substatement.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 3.4, YANG status description extension statement";
}
}
<CODE ENDS>
YANG module with augmentations to YANG Library to revision labels
<CODE BEGINS> file "ietf-yl-revisions@2019-09-18.yang"
module ietf-yl-revisions {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yl-revisions";
prefix yl-rev;
import ietf-yang-revisions {
prefix rev;
reference
"XXXX: Updated YANG Module Revision Handling";
}
import ietf-yang-library {
prefix yanglib;
reference "RFC 8525: YANG Libary";
}
organization
"IETF NETMOD (Network Modeling) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>
Author: Benoit Claise
<mailto:bclaise@cisco.com>
Author: Joe Clarke
<mailto:jclarke@cisco.com>
Author: Reshad Rahman
<mailto:rrahman@cisco.com>
Author: Robert Wilton
<mailto:rwilton@cisco.com>
Author: Kevin D'Souza
<mailto:kd6913@att.com>
Author: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>
Author: Jason Sterne
<mailto:jason.sterne@nokia.com>";
description
"This module contains augmentations to YANG Library to add module
level revision label and to provide an indication of how
deprecated and obsolete nodes are handled by the server.
Copyright (c) 2019 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.
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 (RFC 2119) (RFC 8174) when, and only when,
they appear in all capitals, as shown here.";
// RFC Ed.: update the date below with the date of RFC publication
// and remove this note.
// RFC Ed.: replace XXXX (including in the imports above) with
// actual RFC number and remove this note.
// RFC Ed.: please replace revision-label version with 1.0.0 and
// remove this note.
revision 2019-09-18 {
rev:revision-label 0.1.0;
description
"Initial revision";
reference
"XXXX: Updated YANG Module Revision Handling";
}
augment "/yanglib:yang-library/yanglib:module-set/yanglib:module" {
description
"Augmentation modules with a revision label";
leaf revision-label {
type rev:revision-label;
description
"The revision label associated with this module revision.
The label MUST match the rev:label value in the specific
revision of the module loaded in this module-set.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 5.2.1, Advertising revision-label";
}
}
augment "/yanglib:yang-library/yanglib:schema" {
description
"Augmentations to the ietf-yang-library module to indicate how
deprecated and obsoleted nodes are handled for each datastore
schema supported by the server.";
leaf deprecated-nodes-implemented {
type empty;
description
"If present, this leaf indicates that all schema nodes with a
status 'deprecated' child statement are implemented
equivalently as if they had status 'current', or otherwise
deviations MUST be used to explicitly remove 'deprecated'
nodes from the schema. If this leaf is absent then the
behavior is unspecified.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 5.2.2, Reporting how deprecated and obsolete nodes
are handled";
}
leaf obsolete-nodes-absent {
type empty;
description
"If present, this leaf indicates that the server does not
implement any status 'obsolete' nodes. If this leaf is
absent then the behaviour is unspecified.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 5.2.2, Reporting how deprecated and obsolete nodes
are handled";
}
}
}
CODE ENDS>
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 the design team and have worked on the YANG versioning project:
The initial revision of this document was refactored and built upon [I-D.clacla-netmod-yang-model-update].
Discussons on the use of Semver for YANG versioning has been held with authors of the OpenConfig YANG models. We would like thank both Anees Shaikh and Rob Shakir for their input into this problem space.
The document does not define any new protocol or data model. There are no security impacts.
The following YANG module is requested to be registred in the "IANA Module Names" registry:
The ietf-yang-revisions module:
The ietf-yl-revisions module:
| [I-D.ietf-netmod-rfc6991-bis] | Schoenwaelder, J., "Common YANG Data Types", Internet-Draft draft-ietf-netmod-rfc6991-bis-02, November 2019. |
| [I-D.verdt-netmod-yang-semver] | Claise, B., Clarke, J., Rahman, R., Wilton, R., Lengyel, B., Sterne, J. and K. D'Souza, "YANG Semantic Versioning", Internet-Draft draft-verdt-netmod-yang-semver-01, October 2019. |
| [I-D.verdt-netmod-yang-versioning-reqs] | Clarke, J., "YANG Module Versioning Requirements", Internet-Draft draft-verdt-netmod-yang-versioning-reqs-02, November 2018. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC7895] | Bierman, A., Bjorklund, M. and K. Watsen, "YANG Module Library", RFC 7895, DOI 10.17487/RFC7895, June 2016. |
| [RFC7950] | Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016. |
| [RFC8174] | Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017. |
| [RFC8407] | Bierman, A., "Guidelines for Authors and Reviewers of Documents Containing YANG Data Models", BCP 216, RFC 8407, DOI 10.17487/RFC8407, October 2018. |
| [RFC8525] | Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K. and R. Wilton, "YANG Library", RFC 8525, DOI 10.17487/RFC8525, March 2019. |
| [I-D.clacla-netmod-yang-model-update] | Claise, B., Clarke, J., Lengyel, B. and K. D'Souza, "New YANG Module Update Procedure", Internet-Draft draft-clacla-netmod-yang-model-update-06, July 2018. |
| [I-D.ietf-netmod-yang-instance-file-format] | Lengyel, B. and B. Claise, "YANG Instance Data File Format", Internet-Draft draft-ietf-netmod-yang-instance-file-format-08, March 2020. |
| [I-D.rwilton-netmod-yang-packages] | Wilton, R., Rahman, R., Clarke, J., Sterne, J. and W. Bo, "YANG Packages", Internet-Draft draft-rwilton-netmod-yang-packages-03, February 2020. |
| [I-D.verdt-netmod-yang-solutions] | Wilton, R., "YANG Versioning Solution Overview", Internet-Draft draft-verdt-netmod-yang-solutions-03, February 2020. |
| [I-D.wilton-netmod-yang-ver-selection] | Wilton, R., Rahman, R., Clarke, J., Sterne, J. and W. Bo, "YANG Schema Selection", Internet-Draft draft-wilton-netmod-yang-ver-selection-02, February 2020. |
| [RFC8340] | Bjorklund, M. and L. Berger, "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018. |
| [semver] | "Semantic Versioning 2.0.0" |
Examples of NBC changes include:
The following sections give guidance for how some of these NBC changes could be made to a YANG module:
Removing a leaf or container from the data tree, e.g. because support for the corresponding feature is being removed:
If the server can support NBC versions of the YANG module simultaneously using version selection, then the changes can be done immediately:
Changing the type of a leaf-node. e.g. consider a "vpn-id" node of type integer being changed to a string:
If the server can support NBC versions of the YANG module simultaneously using version selection, then the changes can be done immediately:
Reducing the range of values of a leaf-node. e.g. consider a "vpn-id" node of type integer being changed from type uint32 to type uint16:
Changing the key of a list has a big impact to the client. For example, consider a "sessions" list which has a key "interface" and there is a need to change the key to "dest-address", such a change can be done in steps:
If the server can support NBC versions of the YANG module simultaneously using version selection, then the changes can be done immediately:
A leaf-node or a container may be renamed, either due to a spelling error in the previous name or because of a better name. For example a node "ip-adress" could be renamed to "ip-address":
If the server can support NBC versions of the YANG module simultaneously using version selection, then the changes can be done immediately: