Internet DRAFT - draft-lengyel-netmod-yang-instance-data
draft-lengyel-netmod-yang-instance-data
Network Working Group B. Lengyel
Internet-Draft Ericsson
Intended status: Standards Track B. Claise
Expires: April 6, 2019 Cisco Systems, Inc.
October 3, 2018
YANG Instance Data Files and their use for Documenting Server
Capabilities
draft-lengyel-netmod-yang-instance-data-04
Abstract
This document specifies a standard file format for YANG instance
data, that is data that could be stored in a datastore and whose
syntax and semantics is defined by YANG models. Instance data files
can be used to provide information that is defined in design time.
There is a need to document Server capabilities (which are often
specified in design time). Defining server capabilities is foreseen
as the most important use of YANG instance data files.
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
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This Internet-Draft will expire on April 6, 2019.
Copyright Notice
Copyright (c) 2018 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
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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described in the Simplified BSD License.
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1. Data Life cycle . . . . . . . . . . . . . . . . . . . . . 4
2.2. Delivery of Instance Data . . . . . . . . . . . . . . . . 4
2.3. Use Case 1: Early Documentation of Server Capabilites . . 5
2.4. Use Case 2: Preloading Data . . . . . . . . . . . . . . . 5
2.5. Use Case 3: Dcoumenting Factory Default Settings . . . . 5
3. Instance Data File Format . . . . . . . . . . . . . . . . . . 6
4. YANG Model . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Open Issues . . . . . . . . . . . . . . . . . . . . 11
Appendix B. Changes between revisions . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Terminology
Design time: A time during which a YANG model and the implementation
behind it is created. Sometimes in other documents this period is
divided into design and implementation time.
Instance Data Set: A named set of data items that can be used as
instance data in a YANG data tree.
Instance Data File: A file containing an instance data set formatted
according to the rules described in this document.
Target YANG Module: A YANG module for which the instance data set
contains instance data, like ietf-yang-library in the examples.
2. Introduction
A YANG server has a number of server-capabilities that can be
retrieved from the server using protocols like NETCONF or RESTCONF.
YANG server capabilities include
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o data defined in ietf-yang-library: YANG modules, submodules,
features, deviations, schema-mounts
([I-D.ietf-netconf-rfc7895bis])
o datastores supported
o alarms supported ([I-D.ietf-ccamp-alarm-module])
o data nodes, subtrees that support or do not support on-change
notifications ([I-D.ietf-netconf-yang-push])
o netconf-capabilities
While it is good practice to allow a client to query these
capabilites from the live YANG server, that is often not enough.
Most server-capabilities are relatively stable but the fact is that
some might change. Looking at the change frequency, we have roughly
three categories:
1. only at upgrade, e.g. introduced with a new SW package
2. rarely e.g. due to licensing or HW inserted
3. more frequently e.g. a capability might be dependent on the CPU
or traffic load, although that would be most unusual
Most capabilities belong to type 1), some to type 2) and a relatively
small set to type 3). Many network nodes only have type 1) or type
1+2) capabilities. Stable capabilities are usually defined by a
vendor in design time, before the product is released. While these
capabilities can be retrieved from the live server in run-time, there
is a strong need to provide the same data already during design time.
(Often only a part of all the server capabilities can be made
available.)
Often when a network node is released an associated NMS (network
management system) is also released with it. The NMS depends on the
capabilities of the YANG server. During NMS implementation
information about server capabilities is needed. If the information
is not available early in some off-line document, but only as
instance data from the live network node, the NMS implementation will
be delayed, because it has to wait for the network node to be ready.
Also assuming that all NMS implementors will have a correctly
configured network node available to retrieve data from, is a very
expensive proposition. (An NMS may handle dozens of node types.)
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Beside NMS implementors, system integrators and many others also need
the same information early. Examples could be model driven testing,
generating documentation, etc.
As capabilities are often already known in design time and are
relativaly stable, it feasible and advantageous to define/document
them early. This document specifies a file format for YANG instance
data that may be used to provide server capability information,
allowing vendors to specify capabilities early, in design time.
The same instance data file format can be used for other purposes,
like providing initial data for any YANG module. E.g. a basic set of
access control groups can be provided either by a device vendor or an
operator using the network device.
2.1. Data Life cycle
Data defined or documented in YANG Instance Data Sets may be used for
preloading a YANG server with this data, but the server may populate
the data without using the actual file in which case the Instance
Data File is only used as documentation.
While such data will usually not change, data documented by Instance
Data sets MAY be changed by the YANG server itself or by management
operations. It is out of scope for this document to specify a method
to prevent this. Whether such data changes and if so, when and how,
SHOULD be described either in the instance data file description
statement or in some other implementation specific manner.
YANG Instance data is a snap-shot of information at a specific point
of time. If the data changes afterwards this is not represented in
the instance data set anymore, the valid values can be retrieved in
run-time via Netconf/Restconf
Notifications about the change of data documented by Instance Data
Sets may be supplied by e.g. the Yang-Push mechanism, but it is out
of scope for this document.
2.2. Delivery of Instance Data
Instance data files SHOULD be available without the need for and
before the instalation of a live YANG server e.g. via download from
the vendor's website. or any other way together with other product
documentation.
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2.3. Use Case 1: Early Documentation of Server Capabilites
An operator wants to integrate his own, in-house built management
system with the network node from ACME Systems. The management
integration must be ready by the time the first AcmeRouter is
installed in the network. To do the integration the operator needs
the list of supported YANG modules and features. While this list
could be read from the ietf-yang-library via Netconf, in order to
allow time for developing the management integration, the operator
demands this information early. The operator will value that this
information is available in a standard format, that is actually the
same format that can be read later from the node via Netconf.
YANG instance data files are used to provide design time information
about server capabilities.
2.4. Use Case 2: Preloading Data
There are parts of the configuration that must be fully configurable
by the operator, however for which often a semi-standard default
configuration will be sufficient.
One example is access control groups/roles and related rules. While
a sophisticated operator may define dozens of different groups often
a basic (read-only operator, read-write system administrator,
security-administrator) triplet will be enough. Vendors will often
provide such default configuration data to make device configuration
easier for an operator.
Defining Access control data is a complex task. To help the device
vendor pre-defines a set of default groups (/nacm:nacm/groups) and
rules for these groups to access specific parts of common models
(/nacm:nacm/rule-list/rule).
YANG instance data files are used to document and/or preload the
default configurationp.
2.5. Use Case 3: Dcoumenting Factory Default Settings
Nearly every YANG server has a factory default configuration. If the
system is really badly misconfigured or if the current configuration
is to be abandoned the system can be reset to this default.
In Netconf the <delete-config> operation can be used to do this,
while in Restconf there are plans to introduce a custom operation for
this purpose.
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The operator currently has no way to know what the default
configuration actually contains. YANG Instance data can be used to
document the factory default configuration.
3. Instance Data File Format
Two standard formats to represent YANG Instance Data are specified
based on the XML and JSON encoding. The XML format is based on
[RFC7950] while the JSON format is based on [RFC7951]. Later as
other YANG encodings (e.g. CBOR) are defined further Instance Data
formats may be specified.
For both formats data is placed in a top level auxiliary container
named "instance-data-set". The purpose of the container, which is
not part of the real data itself, is to carry meta-data for the
complete instance-data-set.
The XML format SHALL follow the format returned for a NETCONF GET
operation. The <data> anydata (which is not part of the real data
itself) SHALL contain all data that would be inside the <data>
wrapper element of a reply to the <get> operation. XML attributes
SHOULD NOT be present, however if a SW receiving a YANG instance data
file encounters XML attributes unknown to it, it MUST ignore them,
allowing them to be used later for other purposes.
The JSON format SHALL follow the format of the reply returmed for a
RESTCONF GET request directed at the datastore resource:
{+restconf}/data. ETags and Timestamps SHOULD NOT be included, but
if present SHOULD be ignored.
A YANG Instance data file MUST contain a single instance data set.
Instance data MUST conform to the corresponding target YANG Modules
and follow the XML/JSON encoding rules as defined in [RFC7950] and
[RFC7951] and use UTF-8 character encoding. A single instance data
set MAY contain data for any number of target YANG modules, if needed
it MAY carry the complete configuraton and state data set for a YANG
server. Default values SHOULD NOT but MAY be included. Config=true
and config=false data MAY be mixed in the instance data file.
Instance data files MAY contain partial data sets. This means
mandatory, min-elements or require-instance=true constrains MAY be
violated.
The name of the file SHOULD be of the form:
instance-data-set-name ['@' revision-date] ( '.yid' )
E.g. acme-router-modules@2018-01-25.yid
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The revision date is optional. It SHOULD NOT be used if the file is
stored in a version control system (e.g. git) because the change of
file names will break the connection between the different revisions
of the file.
Meta data, information about the data set itself SHALL be included in
the instance data set. This data will be children of the top level
instance-data-set container as defined in the ietf-instance-data YANG
module. Meta data SHALL include:
o Name of the instance data set
Meta data SHOULD include:
o Revision date of the instance data set
o Description of the instance data set. The description SHOULD
contain information whether and how the data can change during the
lifetime of the YANG server.
<?xml version="1.0" encoding="UTF-8"?>
<instance-data-set xmlns=
"urn:ietf:params:xml:ns:yang:ietf-yang-instance-data">
<name>acme-router-modules</name>
<revision>2108-01-25</revision>
<description>Defines the minimal set of modules that any acme-router
will contain. These modules will always be present.</description>
<contact>info@acme.com</contact>
<data>
<yang-library xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
<module-set>
<name>basic</name>
<module>
<name>ietf-system</>
<revision>2014-08-06</revision>
<!-- description "A later revision may be used."; -->
<namespace>urn:ietf:params:xml:ns:yang:ietf-system</namespace>
<feature>authentication</feature>
<feature>radius-authentication</feature>
</module>
</module-set>
</yang-library>
</data>
</instance-data-set>
Figure 1: XML Instance Data File example
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{
"ietf-yang-instance-data:instance-data-set": {
"name": "acme-router-modules",
"revision": "2108-01-25",
"contact": "info@acme.com",
"description":
"Defines the set of modules that an acme-router will contain.",
"data": {
"ietf-yang-library:yang-library": {
"module-set": [
"name": "basic",
"module": [
{
"name": "ietf-system",
"revision": "2014-08-06",
"namespace": "urn:ietf:params:xml:ns:yang:ietf-system",
"feature": ["authentication", "radius-authentication"]
}
}
]
]
}
}
}
Figure 2: JSON Instance Data File example
4. YANG Model
<CODE BEGINS> file "ietf-yang-instance-data.yang"
module ietf-yang-instance-data {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-yang-instance-data";
prefix yid ;
import ietf-yang-data-ext { prefix yd; }
import ietf-datastores { prefix ds; }
organization "IETF NETMOD Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/netmodf/>
WG List: <mailto:netmod@ietf.org>
Author: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>";
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description "The module defines the structure and content of YANG
Instance Data Sets.";
revision 2018-06-30 {
description "Initial revision.";
reference "RFC XXXX: YANG Instance Data";
}
yd:yang-data instance-data-format {
container instance-data-set {
description "Auxiliary container to carry meta-data for
the complete instance data set.";
leaf name {
type string;
mandatory true;
description "Name of a YANG instance data set.";
}
leaf description { type string; }
leaf contact {
type string;
description "Contains the same information the contact
statement carries for a YANG module.";
}
leaf organization {
type string;
description "Contains the same information the
organization statement carries for a YANG module.";
}
leaf datastore {
type ds:datastore-ref;
description "The identity of the datastore for which
the instance data is documented for config=true data nodes.
The leaf MAY be absent in which case the running dtastore or
if thats not writable, the candidate datastore is implied.
For config=false data nodes always the operational
data store is implied.";
}
list revision {
key date;
description "An instance-data-set SHOULD have at least
one revision entry. For every published
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editorial change, a new one SHOULD be added in front
of the revisions sequence so that all revisions are
in reverse chronological order.";
leaf date {
type string {
pattern '\d{4}-\d{2}-\d{2}';
}
description "Specifies the data the revision
was last modified. Formated as YYYY-MM-DD";
}
leaf description { type string; }
}
anydata data {
mandatory true;
description "Contains the real instance data.
The data MUST conform to the relevant YANG Modules.";
}
}
}
}
<CODE ENDS>
5. Security Considerations
Depending on the nature of the instance data, instance data files MAY
need to be handled in a secure way. The same type of handling should
be applied, that would be needed for the result of a <get> operation
returning the same data.
6. IANA Considerations
To be completed, all the usual requests for a new YANG module
7. References
7.1. Normative References
[I-D.ietf-netmod-yang-data-ext]
Bierman, A., Bjorklund, M., and K. Watsen, "YANG Data
Extensions", draft-ietf-netmod-yang-data-ext-01 (work in
progress), March 2018.
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[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>.
[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG",
RFC 7951, DOI 10.17487/RFC7951, August 2016,
<https://www.rfc-editor.org/info/rfc7951>.
7.2. Informative References
[I-D.ietf-ccamp-alarm-module]
Vallin, S. and M. Bjorklund, "YANG Alarm Module", draft-
ietf-ccamp-alarm-module-03 (work in progress), September
2018.
[I-D.ietf-netconf-rfc7895bis]
Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
and R. Wilton, "YANG Library", draft-ietf-netconf-
rfc7895bis-06 (work in progress), April 2018.
[I-D.ietf-netconf-yang-push]
Clemm, A., Voit, E., Prieto, A., Tripathy, A., Nilsen-
Nygaard, E., Bierman, A., and B. Lengyel, "YANG Datastore
Subscription", draft-ietf-netconf-yang-push-19 (work in
progress), September 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Appendix A. Open Issues
o -
Appendix B. Changes between revisions
v03 - v04
o Updated changelog for v02-v03
v02 - v03
o Updated the document according to comments received at IETF102
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o Added parameter to specify datastore
o Rearranged chapters
o Added new use case: Documenting Factory Default Settings
o Added "Target YANG Module" to terminology
o Clarified that instance data is a snapshot valid at the time of
creation, so it does not contain any later changes.
o Removed topics from Open Issues according to comments received at
IETF102
v01 - v02
o The recommendation to document server capabilities was changed to
be just the primary use-case. (Merged chapter 4 into the use case
chapter.)
o Stated that RFC7950/7951 encoding must be followed which also
defines (dis)allowed whitespace rules.
o Added UTF-8 encoding as it is not specified in t950 for instance
data
o added XML declaration
v00 - v01
o Redefined using yang-data-ext
o Moved meta data into ordinary leafs/leaf-lists
Authors' Addresses
Balazs Lengyel
Ericsson
Magyar Tudosok korutja 11
1117 Budapest
Hungary
Phone: +36-70-330-7909
Email: balazs.lengyel@ericsson.com
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Benoit Claise
Cisco Systems, Inc.
De Kleetlaan 6a b1
1831 Diegem
Belgium
Phone: +32 2 704 5622
Email: bclaise@cisco.com
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