An Architecture for YANG-Push to Message Broker Integration

1.1. Origins of YANG-Push

With [RFC3535] the IAB set the requirements for Network Management in 2003. From these requirements NETCONF [RFC6241], NETCONF Notifications [RFC5277] and RESTCONF [RFC8040] have been defined to configure through <edit-config> and retrieve operational data through <get> and NETCONF notifications through <notification> from a YANG datastore on a network node.¶

With YANG-Push, as defined in [RFC8639], [RFC8640] and [RFC8641], periodical and on-change subscriptions to the YANG datastore can be dynamically or statically configured. When notifications are dynamically configured, messages are published over the initially established NETCONF session, while when it is statically configured messages are published through HTTPS-based [I-D.ietf-netconf-https-notif] or UDP-based [I-D.ietf-netconf-udp-notif] transport. Section 3.7 of [RFC8641] describes push-update messages where the YANG subscribed data is being published, where Section 2.7 of [RFC8639] describes the subscription state change notifications where changes in the subscription are being described.¶

1.2. Origins of Apache Kafka

Apache Kafka [Kaf11] is a Message Broker that supports producing and consuming messages from so called topics. Each topic has one or more partitions where messages are replicated or load balanced to scale out. With the introduction of Confluent Schema Registry [Con18] a topic can contain one or more subjects. A subject refers to a Schema defining the structure of the message. The Schema then is used to validate messages sent through topics and are identified by a Schema ID. The Schema ID is issued when the Schema is registered to the Confluent Schema Registry. Once the Schema ID is obtained, it can be prefixed to the message with a Confluent Schema Registry compatible serializer. Messages can then be validated against Schema at the producer or at the consumer from a topic to ensure Schema integrity of the message. The type of Schema evolution scheme can be defined per subject, wherever non backward compatibility changes are allowed or not.¶

1.3. Document Scope

This document focuses on YANG-Push [RFC8641] as the messaging protocol between the network node and the Network Telemetry [RFC9232] data collection. It describes the main components and the aimed architecture for deploying such solution in a production network. Then, it illustrates the integration of the YANG 1.1 [RFC7950] as a schema modeling language into the Apache Kafka Message Broker and Confluent Schema Registry [Con18].¶

2.1. Terminology

This document defines the following terms:¶

Message Broker: is an intermediary software component that translates messages from the formal messaging protocol of the sender to the formal messaging protocol of the receiver routed in topics. Message brokers are elements in Data Mesh where software applications communicate by exchanging formally-defined messages.¶

Stream Catalog: provides a single point of access that allows users to centrally search semantics for information across a Message Broker.¶

Additionally it makes use of the terms defined in [RFC8639], Apache Kafka [Kaf11] and Confluent Schema Registry Documentation [ConDoc18].¶

The following terms are used as defined in [RFC8639]:¶

• Publisher¶

• Receiver¶

• Subscription¶

• Subscription ID¶

• Event stream filter¶

• Notification message¶

The following terms are used as defined in Apache Kafka Message Broker [Kaf11]:¶

• Producer¶

• Consumer¶

• Topic¶

• Partition¶

The following terms are used as defined in Confluent Schema Registry Documentation [ConDoc18]:¶

• Schema¶

• Schema ID¶

• Schema Registry¶

• Subject¶

3.1. Automatic Onboarding

Automate the Data Mesh onboarding of newly subscribed YANG metrics.¶

3.2. Preserve Schema

The preservation of the YANG schema, that includes the YANG data types as defined in [RFC6991] and the nested structure of the YANG module, throughout the data processing chain ensures that metrics can be processed and visualized as they were originally intended. Not only for users but also for automated closed loop operation actions.¶

3.3. Preserve Semantic Information

[RFC7950] defines in Section 7.21.3 and 7.21.4 the description and reference statement. This information is intended for the user, describing in a human-readable fashion the meaning of a definition. In Data Mesh, this information can be imported from the YANG Schema Registry into a Stream Catalog where subjects within Message Broker are identifiable and searchable. An example of a Stream Catalog is Apache Atlas [Atl15]. It can also be applied for time series data visualization in a similar fashion.¶

3.4. Standardize Data Processing Integration

Since the YANG Schema is preserved for operational metrics in the Message Broker, a standardization for integration between network data collection and stream processor or time series database is implied.¶

4.1. YANG-Push Subscription

With step number (1) in the workflow diagram, the YANG-Push notification transport capabilities are being discovered according to [I-D.netana-netconf-yp-transport-capabilities], notification capabilities according to [I-D.netana-netconf-notif-envelope] and notification subscription capabilities according to Section 3 of [RFC9196], in with step (2) a YANG-Push subscription is according to Section 2.4 and 2.5 of [RFC8639] dynamically or statically configured, and with step (3) subscription state change notifications are sent according to section 2.7 from the YANG-Push publisher to the receiver to inform which event stream filter has been applied to which subscription ID.¶

When the YANG-Push subscription is managed dynamically, the YANG data is being received on the same NETCONF session where the subscription is being maintained. With configured subscription the YANG data is sent to the YANG-Push receiver through a separate transport session.¶

[I-D.ietf-netconf-yang-notifications-versioning] adds the capability to subscribe to a specific YANG module revision or a YANG module which needs to be backward compatible to in step (2) and adds the module name, revision and revision-label information into the subscription state change notifications in step (3).¶

Figure 2 provides and example how to create a YANG-Push configured subscription with NETCONF in XML [W3C.REC-xml-20081126] with UDP-based [I-D.ietf-netconf-udp-notif] transport¶

========== NOTE: '\' line wrapping per RFC 8792) ===========

<rpc message-id="101"
  xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <edit-config>
    <target>
      <running/>
    </target>
    <config>
      <subscriptions xmlns="urn:ietf:params:xml:ns:yang:ietf\
      -subscribed-notifications">
        <subscription>
          <id>6666</id>
          <datastore xmlns="urn:ietf:params:xml:ns:yang:ietf\
          -yang-push"
            xmlns:ds="urn:ietf:params:xml:ns:yang:ietf\
            -datastores">ds:operational</datastore>
          <datastore-xpath-filter xmlns="urn:ietf:params:xml:ns\
          :yang:ietf-yang-push"
            xmlns:if="urn:ietf:params:xml:ns:yang:ietf-inter\
            faces">/if:interfaces</datastore-xpath-filter>
          <revision xmlns="urn:ietf:params:xml:ns:yang:ietf-yang\
          -push-revision">2018-02-20</revision>
          <transport xmlns:unt="urn:ietf:params:xml:ns:yang:ietf\
          -udp-notif-transport">unt:udp-notif</transport>
          <encoding>encode-json</encoding>
          <receivers>
            <receiver>
              <name>subscription-specific-receiver-def</name>
              <receiver-instance-ref xmlns="urn:ietf:params:xml\
              :ns:yang:ietf-subscribed-notif-receivers">\
              global-udp-notif-receiver-def</receiver-instance-ref>
            </receiver>
          </receivers>
          <periodic xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push">
            <period>6000</period>
          </periodic>
        </subscription>
        <receiver-instances xmlns="urn:ietf:params:xml:ns:yang:ietf\
        -subscribed-notif-receivers">
          <receiver-instance>
            <name>global-udp-notif-receiver-def</name>
            <udp-notif-receiver xmlns="urn:ietf:params:xml:ns:yang\
            :ietf-udp-notif-transport">
              <address>192.0.5.1</address>
              <port>12345</port>
              <enable-segmentation>false</enable-segmentation>
              <max-segment-size/>
            </udp-notif-receiver>
          </receiver-instance>
        </receiver-instances>
      </subscriptions>
    </config>
  </edit-config>
</rpc>

Figure 3 provides an example of a JSON encoded, [RFC7951], subscription-started state change notification message over HTTPS-based [I-D.ietf-netconf-https-notif] or UDP-based [I-D.ietf-netconf-udp-notif] transport with [I-D.netana-netconf-notif-envelope], [I-D.tgraf-netconf-yang-push-observation-time] and [I-D.ietf-netconf-yang-notifications-versioning] as extensions for the same subscription.¶

{
  "ietf-yp-notification:envelope": {
    "event-time": "2023-03-25T08:30:11.22Z",
    "hostname": "example-router",
    "sequence-number": 1,
    "notification-contents": {
      "ietf-subscribed-notification:subscription-started": {
        "id": 6666,
        "ietf-yang-push:datastore": "ietf-datastores:operational",
        "ietf-yang-push:datastore-xpath-filter": "/if:interfaces",
        "ietf-yang-push-revision:revision": "2014-05-08",
        "ietf-yang-push-revision:module-name": "ietf-interfaces",
        "ietf-yang-push-revision:revision-label": "",
        "ietf-distributed-notif:message-publisher-ids": [1,2],
        "transport": "ietf-udp-notif-transport:udp-notif",
        "encoding": "encode-json",
        "ietf-yang-push:periodic": {
          "ietf-yang-push:period": 100
                }
      }
    }
  }
}

4.2. YANG-Push Publisher

With step number (4) in the workflow diagram, a YANG-Push push-update or push-change-update message, depending on wherever periodical or on-change subscription has been established, is sent from the YANG-Push publisher to the receiver according to Section 3.7 of [RFC8639].¶

[I-D.netana-netconf-notif-envelope] defines the YANG-Push notification header in YANG with event-time, hostname and sequence-number to enable a YANG data consumer to recognize with the hostname from which network node the message was published from and with sequence-number message reordering or loss.¶

[I-D.ietf-netconf-distributed-notif] adds a message-publisher-id for network nodes with distributed architecture where multiple YANG-Push publishing processes are publishing messages. The message-publisher-id enables a YANG data consumer to recognize from which YANG-Push publisher process the message was published from.¶

[I-D.tgraf-netconf-yang-push-observation-time] adds observation timestamp and point-in-time in the YANG-Push push-update or push-change-update message. observation timestamp contains the timestamp and point-in-time when the metrics where observed. See Section 3 of [I-D.tgraf-netconf-yang-push-observation-time] for more details.¶

Figure 4 provides an example of a JSON encoded, [RFC7951], push-update notification message over HTTPS-based [I-D.ietf-netconf-https-notif] or UDP-based [I-D.ietf-netconf-udp-notif] transport with [I-D.netana-netconf-notif-envelope] and [I-D.tgraf-netconf-yang-push-observation-time] as extensions for the same subscription.¶

========== NOTE: '\' line wrapping per RFC 8792) ===========

{
  "ietf-yp-notification:envelope": {
    "event-time": "2023-03-25T08:30:11.22Z",
    "hostname": "example-router",
    "sequence-number": 1,
    "notification-contents": {
      "ietf-yang-push:push-update": {
        "id": 6666,
        "ietf-yp-observation:timestamp": \
        "2023-03-25T08:30:11.22Z",
        "ietf-yp-observation:point-in-time": \
        "current-accounting",
        "datastore-contents": {
          "ietf-interfaces:interfaces": [
            {
              "interface": {
                "name": "eth0",
                "type": "iana-if-type:ethernetCsmacd",
                "oper-status": "up",
                "mtu": 1500
              }
            }
          }
        ]
      }
    }
  }
}

Figure 5 provides an example of a JSON encoded, [RFC7951], push-change-update notification message over HTTPS-based [I-D.ietf-netconf-https-notif] or UDP-based [I-D.ietf-netconf-udp-notif] transport with [I-D.netana-netconf-notif-envelope] and [I-D.tgraf-netconf-yang-push-observation-time] as extensions for the same subscription.¶

========== NOTE: '\' line wrapping per RFC 8792) ===========

{
  "ietf-yp-notification:envelope": {
    "event-time": "2023-03-25T08:30:11.22Z",
    "hostname": "example-router",
    "sequence-number": 1,
    "notification-contents": {
      "ietf-yang-push:push-change-update": {
        "id": 2222,
        "ietf-yp-observation:timestamp": \
        "2023-03-25T08:30:11.22Z",
        "ietf-yp-observation:point-in-time": \
        "state-changed",
        "datastore-contents": {
          "yang-patch": {
            "patch-id": "patch_54",
            "comment": "Changing encoding to JSON and increasing \
            the period to 10 minutes",
            "edit": [
              {
                "edit-id": "id_change_1",
                "operation": "merge",
                "target": "/ietf-subscribed-notifications\:subs\
                criptions/subscription[id=2222]",
                "value": {
                  "ietf-subscribed-notifications:encoding": \
                  "ietf-subscribed-notifications:encode-json",
                  "ietf-yang-push:periodic": {
                    "period": 60000
                  }
                }
              }
            }
          ]
        }
      }
    }
  }
}

4.3. YANG-Push Receiver

For all the YANG modules and revisions of each sysName and subscription ID in the subscription state change notification received in step number (3) in the workflow diagram, all the YANG module dependencies need to be determined through the YANG Library [RFC8525], and then through NETCONF <get-schema> rpc calls according to [RFC6022] all YANG modules need to be retrieved as described in step (4) in the workflow diagram.¶

[I-D.lincla-netconf-yang-library-augmentation] extends the YANG Library so that not only the submodule but also the augmentation list can be obtained.¶

Figure 9 in Section 4.1 and YANG module in Section 5 of [RFC8641] defines the payload of YANG-push notifications where "datastore-contents" or the "value" of a "push-change-update") is "anydata". [RFC7950] Section 7.10 states that anydata represents an unknown set of nodes that can be modeled with YANG, and the model is not known at design time and that the model of the unknown set of nodes can be signaled through another protocol. This poses and issue in the schema validation of YANG-Push notifications and will be further clarified in point number (1) and (2) in Appendix B.¶

4.4. YANG Schema Registry

The schema registry SHOULD support YANG as the format for defining schema. For each schema registered into the schema registry, a schema ID is returned. That schema ID can be used when interacting with the Message Broker to indicate the schema to use with the message.Ӧ

Confluent Schema Registry is pluggable. Currently Supports AVRO, JSON Schema and Protobuf. The YANG support is being developed at [Yak24] as part of this architecture. Enable to register, obtain and compare [YSR24] YANG Schemas. One YANG Schema with all its augmentations is being registered per YANG-Push subscription ID. for each YANG Schema a locally significant Schema ID is being issued as described in step (7) in the workflow diagram.¶

curl -X POST -H "Content Type: application/vnd.schemaregistry.v1+json"
-d @ietf-interfaces@2018-02-20.json
http://localhost:8081/subjects/ietf-interfaces/

curl http://localhost:8081/subjects/ subjects/ | jq

curl http://localhost:8081/subjects/ietf-interfaces/versions

curl http://localhost:8081/subjects/ietf-interfaces/versions/1

4.5. YANG Message Broker Producer

The previously issued Schema ID is prefixed to the previously in Section 4.3 described metadata augmented YANG push push-update message and serialized to a Message Broker topic in step (8) of the workflow diagram.¶

4.6. YANG Message_Broker Consumer

From the Message Broker topic the message is being consumed and the prefixed Schema ID is being used in step (10) of the workflow diagram to retrieve the YANG Schema to validate the Schema integrity of the message.¶

In order to valida Schema integrity, the event stream filter of the subscription ID in the subscription started or modified message is needed to apply [I-D.aelhassany-anydata-validation] on the YANG schema tree.¶

4.7. YANG Data Consumer

The data storage ingestion specifications are being derived with the in Section 4.6 already retrieved Schema ID and YANG-Push push-update messages can be now ingested and indexed into the data storage table according to their schema in step (12).¶

4.8. YANG Data Storage

The YANG data is being ingested in step (12)according to the previously defined ingestion specification and indexed with the timestamp defined in observation timestamp as defined in [I-D.tgraf-netconf-yang-push-observation-time]. A network operator is now able to query the previously subscribed YANG data.¶

5.1. YANG Schema Registry Extension

Ahmed Elhassany is developing a YANG Schema Extension in Confluent Schema Registry.¶

The source code can be obtained here: [YSR24], the progress report here: [YSRPR24], and was validated at the IETF 117 hackathon.¶

5.2. YANG-Push Receiver Parsing Library

Zhuoyao Lin developed as part of her internship a library to parse YANG-Push subscription notifications, identify YANG module dependencises with YANG Library [RFC8525] and obtain with NETCONF <get-schema> rpc calls [RFC6022] all YANG modules from YANG-Push publisher.¶

The source code can be obtained here: [LYP23] and was validated at the IETF 117 hackathon.¶

5.3. YANG Library Augmented-by Addition

Zhuoyao Lin implemented [I-D.lincla-netconf-yang-library-augmentation] in order to discover augmented-by YANG modules in YANG Library [RFC8525].¶

The source code can be obtained here: [YLA24] and was validated at the IETF 119 hackathon.¶