| NETCONF | A. Clemm |
| Internet-Draft | Huawei |
| Intended status: Standards Track | E. Voit |
| Expires: October 20, 2017 | A. Gonzalez Prieto |
| A. Tripathy | |
| E. Nilsen-Nygaard | |
| Cisco Systems | |
| A. Bierman | |
| YumaWorks | |
| B. Lengyel | |
| Ericsson | |
| April 18, 2017 |
Subscribing to YANG datastore push updates
draft-ietf-netconf-yang-push-06
Providing rapid visibility into changes made on YANG configuration and operational objects enables new capabilities such as remote mirroring of configuration and operational state. Via the mechanism described in this document, subscriber applications may request a continuous, customized stream of updates from a YANG datastore.
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This Internet-Draft will expire on October 20, 2017.
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Traditional approaches to remote visibility have been built on polling. With polling, data is periodically requested and retrieved by a client from a server to stay up-to-date. However, there are issues associated with polling-based management:
A more effective alternative to polling is for an application can receive automatic and continuous updates from a targeted subset of a datastore. Accordingly, there is a need for a service that allows applications to subscribe to updates from a YANG datastore and that enables the publisher to push those updates. The requirements for such a service have been documented in [RFC7923].
This document defines a solution built on top of "Custom Subscription to Event Notifications" [subscribe]. Supplementing that work are YANG data model augmentations, extended RPCs, and new datastore specific update notifications. Transport options for [subscribe] will work seamlessly with this solution.
The terms below supplement those defined in [subscribe].
Data node: An instance of management information in a YANG datastore.
Data node update: A data item containing the current value/property of a Data node at the time the data node update was created.
Datastore: A conceptual store of instantiated management information, with individual data items represented by data nodes which are arranged in hierarchical manner.
Data subtree: An instantiated data node and the data nodes that are hierarchically contained within it.
Notification message: A transport encapsulated update record(s) and/or event notification(s) intended to be sent to a receiver.
Update record: A representation data node update(s) resulting from the application of a filter for a subscription. An update record will include the value/property of one or more data nodes at a point in time. It may contain the update type for each data node (e.g., add, change, delete). Also included may be metadata/headers such as a subscription-id.
Update trigger: A mechanism that determines when a data record is to be generated.
YANG-Push: The subscription and push mechanism for YANG datastores that is specified in this document.
This document specifies a solution for a push update subscription service. This solution supports the dynamic as well as configured subscriptions to information updates from YANG datastores. YANG objects are subsequently pushed from the publisher to the receiver per the terms of the subscription.
YANG-push subscriptions are defined using a data model that is itself defined in YANG. This model enhances the event subscription model defined in [subscribe] with capabilities that allow subscribers to specify what to include in an update record, as well as what triggers the generation of the update record. Key enhancements include:
A dynamic subscription request SHOULD be declined based on publisher's assessment that it may be unable to provide update records that would meet the terms of the request. However a subscriber may quickly follow up with a new subscription request using different parameters.
Random guessing at different parameters by a subscriber is to be discouraged. Therefore to minimize the number of subscription iterations between subscriber and publisher, dynamic subscriptions MUST support a simple negotiation between subscribers and publishers for subscription parameters. This negotiation is in the form of a no-success response to a failed establish or modify subscription request. The no-success message SHOULD include in the returned error information that, when considered, increase the likelihood of success for subsequent requests. However, there are no guarantee that subsequent requests for this subscriber will in fact be accepted.
Such negotiation information returned from a publisher beyond that from [subscribe] include hints at acceptable time intervals, size estimates for the number or objects which would be returned from a filter, and the names of targeted objects not found in the publisher's YANG tree.
On-change subscriptions allow subscribers to subscribe to updates whenever changes to objects occur. As such, on-change subscriptions are effective for data that changes infrequently, yet that require applications to be notified with minimal delay.
On-change subscriptions tend to be more difficult to implement than periodic subscriptions. Accordingly, on-change subscriptions may not be supported by all implementations or for every object. Therefore when an on-change subscription is established, it is important to remember that two criteria MUST be met before objects may be sent. First the a change in a subscribed object supporting on-change notification is detected (for more on how objects are so marked, see Section 3.9). And second, security protections equivalent to a GET on that object permit the object's distribution to a receiver.
To avoid flooding receivers with repeated updates for fast-changing objects, or objects with oscillating values, an on-change subscription allows for the definition of a dampening period. Once an update record for a given object is generated, no other updates for this particular subscription will be created until the end of the dampening period. Values sent at the end of the dampening period are the current values of all changed objects which are current at the time the dampening period expires. Changed objects includes those which were deleted or newly created during that dampening period. If an object has returned to its original value (or even has been created and then deleted) during the dampening-period, the last change will still be sent. This will indicate churn is occuring on that object.
On-change subscriptions can be refined to let users subscribe only to certain types of changes, for example, only to object creations and deletions, but not to modifications of object values. Care must be used with this capability as the remote datastore extract can de-synchronize.
Subscribed data is encoded in either XML or JSON format. A publisher MUST support XML encoding and MAY support JSON encoding.
In a periodic subscription, the data included as part of an update corresponds to data that could have been simply retrieved using a get operation and is encoded in the same way. XML encoding rules for data nodes are defined in [RFC7950]. JSON encoding rules are defined in [RFC7951].
In an on-change subscription, updates need to indicate not only values of changed data nodes but also the types of changes that occurred since the last update. Therefore encoding rules for data in on-change updates will follow YANG-patch operation as specified in [RFC8072]. The YANG-patch will describe what needs to be applied to the earlier state reported by the preceding update, to result in the now-current state. Note that contrary [RFC8072], objects encapsulated are not restricted to configuration objects only.
Subscription policy specifies both the filters and the datastores against which the filters will be applied. The result is the push of information necessary to remotely maintain an extract of publisher's datastore.
Only a single filter can be applied to a subscription at a time. The following filter types are included in the yang-push data model, and may be applied against a datastore:
Xpath itself provides powerful filtering constructs, and care must be used in filter definition. As an example, consider an xpath filter with a boolean result; such a result will not provide an easily interpretable subset of a datastore. Beyond the boolean example, it is quite possible to define an xpath filter where results are easy for an application to mis-interpret. Consider an xpath filter which only passes a datastore object when interface=up. It is up to the receiver to understand implications of the presence or absence of objects in each update.
It is not expected that implementations will support comprehensive filter syntax and boundless complexity. It will be up to implementations to describe what is viable, but the goal is to provide equivalent capabilities to what is available with a GET. Implementations MUST reject dynamic subscriptions or suspend configured subscriptions if they include filters which are unsupportable on a platform.
Contrary to traditional data retrieval requests, datastore subscription enables an unbounded series of update records to be streamed over time. Two generic notifications for update records have been defined for this: "push-update" and "push-change-update".
A push-update notification defines a complete, filtered update of the datastore per the terms of a subscription. This type of notification is used for continuous updates of periodic subscriptions. A push-update notification can also used be for the on-change subscriptions in two cases. First it will be used as the initial push-update if there is a need to synchronize the receiver at the start of a new subscription. It also MAY be sent if the publisher later chooses to resynch an on-change subscription. The push-update record contains a data snippet that contains an instantiated subtree with the subscribed contents. The content of the update record is equivalent to the contents that would be obtained had the same data been explicitly retrieved using e.g., a NETCONF "get" operation, with the same filters applied.
A push-change-update notification is the most common type of update for on-change subscriptions. The update record in this case contains a data snippet that indicates the full set of changes that data nodes have undergone since the last notification of YANG objects. In other words, this indicates which data nodes have been created, deleted, or have had changes to their values.
These new YANG notifications are encoded and placed within notification messages, which are then queued for egress over the specified transport. The following is an example of an XML encoded notification message over NETCONF transport as per [netconf-notif].
<notification
xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2015-03-09T19:14:56Z</eventTime>
<push-update
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<subscription-id>1011</subscription-id>
<time-of-update>2015-03-09T19:14:56.233Z</time-of-update>
<datastore-contents>
<foo>
<bar>some_string</bar>
</foo>
</datastore-contents>
</push-update>
</notification>
Figure 1: Push example
The following is an example of an on-change notification. It contains an update for subscription 89, including a new value for a leaf called beta, which is a child of a top-level container called alpha:
<notification
xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2015-03-09T19:14:56Z</eventTime>
<push-change-update xmlns=
"urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<subscription-id>89</subscription-id>
<time-of-update>2015-03-09T19:14:56.233Z</time-of-update>
<datastore-changes>
<alpha xmlns="http://example.com/sample-data/1.0" >
<beta>1500</beta>
</alpha>
</datastore-changes>
</push-change-update>
</notification>
Figure 2: Push example for on change
The equivalent update when requesting json encoding:
<notification
xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2015-03-09T19:14:56Z</eventTime>
<push-change-update xmlns=
"urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<subscription-id>89</subscription-id>
<time-of-update>2015-03-09T19:14:56.233Z</time-of-update>
<datastore-changes>
{
"ietf-yang-patch:yang-patch": {
"patch-id": [
null
],
"edit": [
{
"edit-id": "edit1",
"operation": "merge",
"target": "/alpha/beta",
"value": {
"beta": 1500
}
}
]
}
}
</datastore-changes>
</push-change-update>
</notification>
Figure 3: Push example for on change with JSON
When the beta leaf is deleted, the publisher may send
<notification
xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2015-03-09T19:14:56Z</eventTime>
<push-change-update xmlns=
"urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<subscription-id>89</subscription-id>
<time-of-update>2015-03-09T19:14:56.233Z</time-of-update>
<datastore-changes-xml>
<alpha xmlns="http://example.com/sample-data/1.0" >
<beta urn:ietf:params:xml:ns:netconf:base:1.0:
operation="delete"/>
</alpha>
</datastore-changes-xml>
</push-change-update>
</notification>
Figure 4: 2nd push example for on change update
[subscribe] has been enhanced to support YANG datastore subscription negotiation. These enhancements provide information on why a datastore subscription attempt has failed.
A datastore subscription can be rejected for multiple reasons. This includes the lack of read authorization on a requested data node, or the inability of the publisher push update records as frequently as requested. In such cases, no subscription is established. Instead, the subscription-result with the failure reason is returned as part of the RPC response. As part of this response, a set of alternative subscription parameters MAY be returned that would likely have resulted in acceptance of the subscription request. The subscriber may consider these as part of future subscription attempts.
It should be noted that a rejected subscription does not result in the generation of an rpc-reply with an rpc-error element, as neither the specification of YANG-push specific errors nor the specification of additional data parameters to be returned in an error case are supported as part of a YANG data model.
For instance, for the following request:
<netconf:rpc message-id="101"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<establish-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<datastore>push-update</datastore>
<filter netconf:type="xpath"
xmlns:ex="http://example.com/sample-data/1.0"
select="/ex:foo"/>
<period>500</period>
<encoding>encode-xml</encoding>
</establish-subscription>
</netconf:rpc>
Figure 5: Establish-Subscription example
the publisher might return:
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<subscription-result
xmlns="http://urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
error-insufficient-resources
</subscription-result>
<period>2000</period>
</rpc-reply>
Figure 6: Error response example
A receiver of subscription data MUST only be sent updates for which they have proper authorization. Data that is being pushed therefore needs to be subjected to a filter that applies all corresponding rules applicable at the time of a specific pushed update, silently removing any non-authorized data from subtrees. This enables YANG data pushed based on subscriptions to be authorized equivalently to a regular data retrieval (get) operation.
The applicable authorization model for data in YANG datastores is the NETCONF Access Control Model [RFC6536]. However, some clarifications to that RFC are needed so that the desired access control behavior is applied to pushed updates.
One of these clarifications is that a dynamic subscriber MUST have read access to every data node specifically named within the filter.
+-------------+ +-------------+
subscription | protocol | | target |
request --> | operation | -------------> | data node |
| allowed? | datastore | access |
+-------------+ or state | allowed? |
data access +-------------+
Figure 7: Access control for subscription
Likewise if a receiver no longer has read access permission to a data node named/targeted within a filter, a dynamic subscription MUST be abnormally terminated (with data-unavailable provided as the reason). To provide equivalent behavior, configured subscriptions MUST be suspended to a receiver.
Another clarification to [RFC6536] is that each of the individual nodes in a pushed update MUST also have access control applied. This includes verifying read access into nodes added since the last update record. If read access into previously accessible nodes not explicitly named in the filter are lost mid-subscription, that can be treated as a 'delete' for on-change subscriptions. If not capable of handling such permission changes for dynamic subscriptions, publisher implementations MAY choose to terminate the subscription and to force re-establishment with appropriate filtering. But this is not optimal.
+-------------+ +-------------------+
subscription | data node | yes | |
update --> | access | ---> | add data node |
| allowed? | | to update message |
+-------------+ +-------------------+
Figure 8: Access control for push updates
In some cases, a publisher supporting on-change notifications may not be able to push updates for some object types on-change. Reasons for this might be that the value of the data node changes frequently (e.g., [RFC7223]'s in-octets counter), that small object changes are frequent and meaningless (e.g., a temperature gauge changing 0.1 degrees), or that the implementation is not capable of on-change notification for a particular object.
Support for on-change notification is usually specific to the individual YANG model and/or implementation so it is possible to define in design time. System integrators need this information (without reading any data from a live node).
The default assumption is that no data nodes support on-change notification. Schema nodes and subtrees that support on-change notifications MUST be marked as such with the YANG extension notifiable-on-change. This extension is defined in the data model below.
When an on-change subscription is established data-nodes marked with notifiable-on-change false; will be automatically filtered out. This also means that authorization checks SHALL NOT be performed on them.
If a YANG model designer wants to add the notifiable-on-change statement to one or more nodes of an existing module, but wants to avoid modifying the text of the existing module, the notifiable-on-change statement MAY be added using deviation statements.
deviation /sys:system/sys:system-time {
deviate add {
yp:notifiable-on-change false;
}
}
Figure 9: Deviation Example
Particularly in the case of on-change push updates, it is important that push updates do not get lost.
Update messages for a single subscription MAY NOT be resequenced.
It is conceivable that under certain circumstances, a publisher will recognize that it is unable to include within an update record the full set of objects desired per the terms of a subscription. In this case, the publisher MUST take one or more of the following actions.
Depending on the subscription, the volume of updates can become quite large. Additionally, based on the platform, it is possible that update records for a single subscription are best sent independently from different line-cards. Therefore, it may not always be practical to send the entire update record in a single chunk. Implementations may therefore choose, at their discretion, to "chunk" update records, breaking one subscription's objects across several update records. In this case the updates-not-sent flag will indicate that no single update record is complete, and there may be multiple updates coming into a receiver for a single periodic interval or on-change dampening period.
Care must be taken in chunking as problems may arrise for objects that have containment or referential dependencies. The publisher must consider these issues if chunking is provided.
It is far preferable to decline a subscription request then to accept such a request when it cannot be met.
Whether or not a subscription can be supported will be determined by a combination of several factors such as the subscription policy (on-change or periodic), the period in which to report changes (1 second periods will consume more resources than 1 hour periods), the amount of data in the subtree that is being subscribed to, and the number and combination of other subscriptions that are concurrently being serviced.
The YANG data model for datastore push subscriptions is depicted in the following figure. Following YANG tree convention in the depiction, brackets enclose list keys, "rw" means configuration, "ro" operational state data, "?" designates optional nodes, "*" designates nodes that can have multiple instances. Parentheses with a name in the middle enclose choice and case nodes. New YANG objects defined here (i.e., beyond those from [subscribe]) are identified with "yp".
module: ietf-subscribed-notifications
+--rw filters
| +--rw filter* [identifier]
| +--rw identifier filter-id
| +--rw filter-type filter-type
| +--rw filter
+--rw subscription-config {configured-subscriptions}?
| +--rw subscription* [identifier]
| +--rw identifier subscription-id
| +--rw encoding? encoding
| +--rw (target)
| | +--:(event-stream)
| | | +--rw stream stream
| | +--:(yp:datastore)
| | +--rw yp:datastore datastore
| +--rw (applied-filter)
| | +--:(by-reference)
| | | +--rw filter-ref filter-ref
| | +--:(locally-configured)
| | +--rw filter-type filter-type
| | +--rw filter
| +--rw stop-time? yang:date-and-time
| +--rw receivers
| | +--rw receiver* [address port]
| | +--rw address inet:host
| | +--rw port inet:port-number
| | +--rw protocol? transport-protocol
| +--rw (notification-origin)?
| | +--:(interface-originated)
| | | +--rw source-interface? if:interface-ref
| | +--:(address-originated)
| | +--rw source-vrf? string
| | +--rw source-address inet:ip-address-no-zone
| +--rw (yp:update-trigger)?
| | +--:(yp:periodic)
| | | +--rw yp:period yang:timeticks
| | | +--rw yp:anchor-time? yang:date-and-time
| | +--:(yp:on-change) {on-change}?
| | +--rw yp:dampening-period yang:timeticks
| | +--rw yp:no-synch-on-start? empty
| | +--rw yp:excluded-change* change-type
| +--rw yp:dscp? inet:dscp
| +--rw yp:weighting? uint8
| +--rw yp:dependency? sn:subscription-id
+--ro subscriptions
+--ro subscription* [identifier]
+--ro identifier subscription-id
+--ro configured-subscription?
| empty {configured-subscriptions}?
+--ro encoding? encoding
+--ro (target)
| +--:(event-stream)
| | +--ro stream stream
| | +--ro replay-start-time? yang:date-and-time {replay}?
| +--:(yp:datastore)
| +--ro yp:datastore datastore
+--ro (applied-filter)
| +--:(by-reference)
| | +--ro filter-ref filter-ref
| +--:(locally-configured)
| +--ro filter-type filter-type
| +--ro filter
+--ro stop-time? yang:date-and-time
+--ro (notification-origin)?
| +--:(interface-originated)
| | +--ro source-interface? if:interface-ref
| +--:(address-originated)
| +--ro source-vrf? string
| +--ro source-address inet:ip-address-no-zone
+--ro receivers
| +--ro receiver* [address port]
| +--ro address inet:host
| +--ro port inet:port-number
| +--ro protocol? transport-protocol
| +--ro pushed-notifications? yang:counter64
| +--ro excluded-notifications? yang:counter64
| +--ro status subscription-status
+--ro (yp:update-trigger)?
| +--:(yp:periodic)
| | +--ro yp:period yang:timeticks
| | +--ro yp:anchor-time? yang:date-and-time
| +--:(yp:on-change) {on-change}?
| +--ro yp:dampening-period yang:timeticks
| +--ro yp:no-synch-on-start? empty
| +--ro yp:excluded-change* change-type
+--ro yp:dscp? inet:dscp
+--ro yp:weighting? uint8
+--ro yp:dependency? sn:subscription-id
rpcs:
+---x establish-subscription
| +---w input
| | +---w encoding? encoding
| | +---w (target)
| | | +--:(event-stream)
| | | | +---w stream stream
| | | | +---w replay-start-time? yang:date-and-time {replay}?
| | | +--:(yp:datastore)
| | | +---w yp:datastore datastore
| | +---w (applied-filter)
| | | +--:(by-reference)
| | | | +---w filter-ref filter-ref
| | | +--:(locally-configured)
| | | +---w filter-type filter-type
| | | +---w filter
| | +---w stop-time? yang:date-and-time
| | +---w (yp:update-trigger)?
| | | +--:(yp:periodic)
| | | | +---w yp:period yang:timeticks
| | | | +---w yp:anchor-time? yang:date-and-time
| | | +--:(yp:on-change) {on-change}?
| | | +---w yp:dampening-period yang:timeticks
| | | +---w yp:no-synch-on-start? empty
| | | +---w yp:excluded-change* change-type
| | +---w yp:dscp? inet:dscp
| | +---w yp:weighting? uint8
| | +---w yp:dependency? sn:subscription-id
| +--ro output
| +--ro subscription-result subscription-result
| +--ro (result)?
| +--:(no-success)
| | +--ro filter-failure? string
| | +--ro replay-start-time-hint? yang:date-and-time
| | +--ro yp:period-hint? yang:timeticks
| | +--ro yp:error-path? string
| | +--ro yp:object-count-estimate? uint32
| | +--ro yp:object-count-limit? uint32
| | +--ro yp:kilobytes-estimate? uint32
| | +--ro yp:kilobytes-limit? uint32
| +--:(success)
| +--ro identifier subscription-id
+---x modify-subscription
| +---w input
| | +---w identifier? subscription-id
| | +---w (applied-filter)
| | | +--:(by-reference)
| | | | +---w filter-ref filter-ref
| | | +--:(locally-configured)
| | | +---w filter-type filter-type
| | | +---w filter
| | +---w stop-time? yang:date-and-time
| | +---w (yp:update-trigger)?
| | +--:(yp:periodic)
| | | +---w yp:period yang:timeticks
| | | +---w yp:anchor-time? yang:date-and-time
| | +--:(yp:on-change) {on-change}?
| | +---w yp:dampening-period yang:timeticks
| +--ro output
| +--ro subscription-result subscription-result
| +--ro (result)?
| +--:(no-success)
| +--ro filter-failure? string
| +--ro yp:period-hint? yang:timeticks
| +--ro yp:error-path? string
| +--ro yp:object-count-estimate? uint32
| +--ro yp:object-count-limit? uint32
| +--ro yp:kilobytes-estimate? uint32
| +--ro yp:kilobytes-limit? uint32
+---x delete-subscription
| +---w input
| | +---w identifier subscription-id
| +--ro output
| +--ro subscription-result subscription-result
+---x kill-subscription
+---w input
| +---w identifier subscription-id
+--ro output
+--ro subscription-result subscription-result
notifications:
+---n replay-complete
| +--ro identifier subscription-id
+---n notification-complete
| +--ro identifier subscription-id
+---n subscription-started
| +--ro identifier subscription-id
| +--ro encoding? encoding
| +--ro (target)
| | +--:(event-stream)
| | | +--ro stream stream
| | | +--ro replay-start-time? yang:date-and-time {replay}?
| | +--:(yp:datastore)
| | +--ro yp:datastore datastore
| +--ro (applied-filter)
| | +--:(by-reference)
| | | +--ro filter-ref filter-ref
| | +--:(locally-configured)
| | +--ro filter-type filter-type
| | +--ro filter
| +--ro stop-time? yang:date-and-time
| +--ro (yp:update-trigger)?
| | +--:(yp:periodic)
| | | +--ro yp:period yang:timeticks
| | | +--ro yp:anchor-time? yang:date-and-time
| | +--:(yp:on-change) {on-change}?
| | +--ro yp:dampening-period yang:timeticks
| | +--ro yp:no-synch-on-start? empty
| | +--ro yp:excluded-change* change-type
| +--ro yp:dscp? inet:dscp
| +--ro yp:weighting? uint8
| +--ro yp:dependency? sn:subscription-id
+---n subscription-resumed
| +--ro identifier subscription-id
+---n subscription-modified
| +--ro identifier subscription-id
| +--ro encoding? encoding
| +--ro (target)
| | +--:(event-stream)
| | +--ro stream stream
| | +--ro replay-start-time? yang:date-and-time {replay}?
| +--ro (applied-filter)
| | +--:(by-reference)
| | | +--ro filter-ref filter-ref
| | +--:(locally-configured)
| | +--ro filter-type filter-type
| | +--ro filter
| +--ro stop-time? yang:date-and-time
| +--ro (yp:update-trigger)?
| | +--:(yp:periodic)
| | | +--ro yp:period yang:timeticks
| | | +--ro yp:anchor-time? yang:date-and-time
| | +--:(yp:on-change) {on-change}?
| | +--ro yp:dampening-period yang:timeticks
| | +--ro yp:no-synch-on-start? empty
| | +--ro yp:excluded-change* change-type
| +--ro yp:dscp? inet:dscp
| +--ro yp:weighting? uint8
| +--ro yp:dependency? sn:subscription-id
+---n subscription-terminated
| +--ro identifier subscription-id
| +--ro error-id subscription-errors
| +--ro filter-failure? string
+---n subscription-suspended
+--ro identifier subscription-id
+--ro error-id subscription-errors
+--ro filter-failure? string
module: ietf-yang-push
notifications:
+---n push-update
| +--ro subscription-id sn:subscription-id
| +--ro time-of-update? yang:date-and-time
| +--ro updates-not-sent? empty
| +--ro datastore-contents?
+---n push-change-update {on-change}?
+--ro subscription-id sn:subscription-id
+--ro time-of-update? yang:date-and-time
+--ro updates-not-sent? empty
+--ro datastore-changes?
Figure 10: Model structure
Selected components of the model are summarized below.
Both configured and dynamic subscriptions are represented within the list subscription-config. Each subscription has own list elements. New and enhanced parameters extending the basic subscription data model in [subscribe] include:
OAM notifications and mechanism are reused from [subscribe]. Some have been augmented to include the YANG datastore specific objects.
The data model introduces two YANG notifications to encode information for update records: "push-update" and "push-change-update".
"Push-update" is used to send a complete snapshot of the filtered subscription data. This type of notification is used to carry the update records of a periodic subscription. The "push-update" notification is also used with on-change subscriptions for the purposes of allowing a receiver to "synch" on a complete set of subscribed datastore contents. This synching may be done the start of an on-change subscription, and then later in that subscription to force resynchronization. If the "updates-not-sent" flag is set, this indicates that the update record is incomplete.
"Push-change-update" is used to send datastore changes that have occurred in subscribed data since the previous update. This notification is used only in conjunction with on-change subscriptions. This will be encoded as yang-patch data.
If the application detects an informational discontinuity in either notification, the notification MUST include a flag "updates-not-sent". This flag which indicates that not all changes which have occurred since the last update are actually included with this update. In other words, the publisher has failed to fulfill its full subscription obligations. (For example a datastore missed a window in providing objects to a publisher process.) To facilitate synchronization, a publisher MAY subsequently send a push-update containing a full snapshot of subscribed data.
YANG-Push subscriptions are established, modified, and deleted using RPCs augmented from [subscribe].
The subscriber sends an establish-subscription RPC with the parameters in section 3.1. An example might look like:
<netconf:rpc message-id="101"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<establish-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<filter netconf:type="xpath"
xmlns:ex="http://example.com/sample-data/1.0"
select="/ex:foo"/>
<period>500</period>
<encoding>encode-xml</encoding>
</establish-subscription>
</netconf:rpc>
Figure 11: Establish-subscription RPC
The publisher MUST respond explicitly positively (i.e., subscription accepted) or negatively (i.e., subscription rejected) to the request. Positive responses include the subscription-id of the accepted subscription. In that case a publisher MAY respond:
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<subscription-result
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
ok
</subscription-result>
<subscription-id
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
52
</subscription-id>
</rpc-reply>
Figure 12: Establish-subscription positive RPC response
A subscription can be rejected for multiple reasons, including the lack of authorization to establish a subscription, the lack of read authorization on the requested data node, or the inability of the publisher to provide a stream with the requested semantics.
When the requester is not authorized to read the requested data node, the returned information indicates the node is unavailable. For instance, if the above request was unauthorized to read node "ex:foo" the publisher may return:
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<subscription-result
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
subtree-unavailable
</subscription-result>
<filter-failure
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
/ex:foo
</filter-failure>
</rpc-reply>
Figure 13: Establish-subscription access denied response
If a request is rejected because the publisher is not able to serve it, the publisher SHOULD include in the returned error what subscription parameters would have been accepted for the request. However, there are no guarantee that subsequent requests using this info will in fact be accepted.
For example, for the following request:
<netconf:rpc message-id="101"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<establish-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<datastore>running</datastore>
<filter netconf:type="xpath"
xmlns:ex="http://example.com/sample-data/1.0"
select="/ex:foo"/>
<dampening-period>10</dampening-period>
<encoding>encode-xml</encoding>
</establish-subscription>
</netconf:rpc>
Figure 14: Establish-subscription request example 2
a publisher that cannot serve on-change updates but periodic updates might return the following:
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<subscription-result
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
period-unsupported
</subscription-result>
<period-hint>100</period-hint>
</rpc-reply>
Figure 15: Establish-subscription error response example 2
The subscriber MAY invoke the modify-subscription RPC for a subscription it previously established. The subscriber will include newly desired values in the modify-subscription RPC. Parameters not included MUST remain unmodified. Below is an example where a subscriber attempts to modify the period of a subscription.
<netconf:rpc message-id="102"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<modify-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<datastore>running</datastore>
<subscription-id>
1011
</subscription-id>
<period>250</period>
</modify-subscription>
</netconf:rpc>
Figure 16: Modify subscription request
The publisher MUST respond explicitly positively or negatively to the request. A response to a successful modification might look like:
<rpc-reply message-id="102"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<subscription-result
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
ok
</subscription-result>
</rpc-reply>
Figure 17: Modify subscription response
If the subscription modification is rejected, the publisher MUST send a response like it does for an establish-subscription and maintain the subscription as it was before the modification request. Responses MAY include hints. A subscription MAY be modified multiple times.
A configured subscription cannot be modified using modify-subscription RPC. Instead, the configuration needs to be edited as needed.
To stop receiving updates from a subscription and effectively delete a subscription that had previously been established using an establish-subscription RPC, a subscriber can send a delete-subscription RPC, which takes as only input the subscription-id. For example:
<netconf:rpc message-id="103"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<delete-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<subscription-id>
1011
</subscription-id>
</delete-subscription>
</netconf:rpc>
<rpc-reply message-id="103"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<subscription-result
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
ok
</subscription-result>
</rpc-reply>
Figure 18: Delete subscription
Configured subscriptions cannot be deleted via RPC, but have to be removed from the configuration.
To make subscription requests, the subscriber needs to know the YANG module library available on the publisher. The YANG 1.0 module library information is sent by a NETCONF server in the NETCONF 'hello' message. For YANG 1.1 modules and all modules used with the RESTCONF [RFC8040] protocol, this information is provided by the YANG Library module (ietf-yang-library.yang from [RFC7895]. The YANG library information is important for the receiver to reproduce the set of object definitions used by the replicated datastore.
The YANG library includes a module list with the name, revision, enabled features, and applied deviations for each YANG module implemented by the publisher. The receiver is expected to know the YANG library information before starting a subscription. The "/modules-state/module-set-id" leaf in the "ietf-yang-library" module can be used to cache the YANG library information.
The set of modules, revisions, features, and deviations can change at run-time (if supported by the server implementation). In this case, the receiver needs to be informed of module changes before data nodes from changed modules can be processed correctly. The YANG library provides a simple "yang-library-change" notification that informs the client that the library has changed. The receiver then needs to re-read the entire YANG library data for the replicated server in order to detect the specific YANG library changes. The "ietf-netconf-notifications" module defined in [RFC6470] contains a "netconf-capability-change" notification that can identify specific module changes. For example, the module URI capability of a newly loaded module will be listed in the "added-capability" leaf-list, and the module URI capability of an removed module will be listed in the "deleted-capability" leaf-list.
<CODE BEGINS> file "ietf-yang-push.yang"
module ietf-yang-push {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-push";
prefix yp;
import ietf-inet-types {
prefix inet;
}
import ietf-yang-types {
prefix yang;
}
import ietf-subscribed-notifications {
prefix sn;
}
organization "IETF";
contact
"WG Web: <http://tools.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
WG Chair: Mahesh Jethanandani
<mailto:mjethanandani@gmail.com>
WG Chair: Mehmet Ersue
<mailto:mehmet.ersue@nokia.com>
Editor: Alexander Clemm
<mailto:ludwig@clemm.org>
Editor: Eric Voit
<mailto:evoit@cisco.com>
Editor: Alberto Gonzalez Prieto
<mailto:albertgo@cisco.com>
Editor: Ambika Prasad Tripathy
<mailto:ambtripa@cisco.com>
Editor: Einar Nilsen-Nygaard
<mailto:einarnn@cisco.com>
Editor: Andy Bierman
<mailto:andy@yumaworks.com>
Editor: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>";
description
"This module contains conceptual YANG specifications
for YANG push.";
revision 2017-04-19 {
description
"Move to identities for filters, datastores.";
reference
"YANG Datastore Push, draft-ietf-netconf-yang-push-06";
}
/*
* EXTENSIONS
*/
extension notifiable-on-change {
argument "value";
description
"Indicates whether changes to the data node are reportable in
on-change subscriptions.
The statement MUST only be a substatement of the leaf, leaf-list,
container, list, anyxml, anydata statements. Zero or One
notifiable-on-change statement is allowed per parent statement.
NO substatements are allowed.
The argument is a boolean value indicating whether on-change
notifications are supported. If notifiable-on-change is not
specified, the default is the same as the parent data node's
value. For top level data nodes the default value is false.";
}
/*
* FEATURES
*/
feature on-change {
description
"This feature indicates that on-change updates are
supported.";
}
/*
* IDENTITIES
*/
/* Error type identities for datastore subscription */
identity period-unsupported {
base sn:error;
description
"Requested time period is too short. This can be for both
periodic and on-change dampening.";
}
identity qos-unsupported {
base sn:error;
description
"Subscription QoS parameters not supported on this platform.";
}
identity dscp-unavailable {
base sn:error;
description
"Requested DSCP marking not allocatable.";
}
identity on-change-unsupported {
base sn:error;
description
"On-change not supported.";
}
identity synch-on-start-unsupported {
base sn:error;
description
"On-change synch-on-start not supported.";
}
identity synch-on-start-datatree-size {
base sn:error;
description
"Synch-on-start would push a datatree which exceeds size limit.";
}
identity reference-mismatch {
base sn:error;
description
"Mismatch in filter key and referenced yang subtree.";
}
identity data-unavailable {
base sn:error;
description
"Referenced yang node or subtree doesn't exist, or read
access is not permitted.";
}
identity datatree-size {
base sn:error;
description
"Resulting push updates would exceed size limit.";
}
/* Datastore identities */
identity datastore {
description
"A datastore.";
}
identity candidate {
base datastore;
description
"The candidate datastore per RFC-6241.";
reference "RFC-6241, #5.1";
}
identity running {
base datastore;
description
"The running datastore per RFC-6241.";
reference "RFC-6241, #5.1";
}
identity startup {
base datastore;
description
"The startup datastore per RFC-6241.";
reference "RFC-6241, #5.1";
}
identity operational {
base datastore;
description
"The operational datastore contains all configuration data
actually used by the system, including all applied configuration,
system-provided configuration and values defined by any supported
data models. In addition, the operational datastore also
contains state data.";
reference
"the original text came from draft-ietf-netmod-revised-datastores
-01, section #4.3. This definition is expected to remain stable
meaning later reconciliation between the drafts unnecessary.";
}
/* New filter identities (adds to 'sn') */
identity subtree {
base sn:filter;
description
"A filter which follows the subtree filter syntax specified
in RFC 6241.";
reference "RFC 6241 section 6";
}
/*
* TYPE DEFINITIONS
*/
typedef change-type {
type enumeration {
enum "create" {
description
"Create a new data resource if it does not already exist. If
it already exists, replace.";
}
enum "delete" {
description
"Delete a data resource if it already exists. If it does not
exists, take no action.";
}
enum "insert" {
description
"Insert a new user-ordered data resource";
}
enum "merge" {
description
"merge the edit value with the target data resource; create
if it does not already exist";
}
enum "move" {
description
"Reorder the target data resource";
}
enum "replace" {
description
"Replace the target data resource with the edit value";
}
enum "remove" {
description
"Remove a data resource if it already exists ";
}
}
description
"Specifies different types of datastore changes.";
reference
"RFC 8072 section 2.5, with a delta that it is ok to receive
ability create on an existing node, or recieve a delete on a
missing node.";
}
typedef datastore {
type identityref {
base datastore;
}
description
"Specifies a system-provided datastore. May also specify ability
portion of a datastore, so as to reduce the filtering effort.";
}
/*
* GROUP DEFINITIONS
*/
grouping datastore-criteria {
description
"A reusable place to define the meaning of datastore.";
leaf datastore {
type datastore;
mandatory true;
description
"Datastore against which the subscription has been applied.";
}
}
grouping update-policy-modifiable {
description
"This grouping describes the datastore specific subscription
conditions that can be changed during the lifetime of the
subscription.";
choice update-trigger {
description
"Defines necessary conditions for sending an event to
the subscriber.";
case periodic {
description
"The agent is requested to notify periodically the current
values of the datastore as defined by the filter.";
leaf period {
type yang:timeticks;
mandatory true;
description
"Duration of time which should occur between periodic
push updates. Where the anchor of a start-time is
available, the push will include the objects and their
values which exist at an exact multiple of timeticks
aligning to this start-time anchor.";
}
leaf anchor-time {
type yang:date-and-time;
description
"Designates a timestamp from which the series of periodic
push updates are computed. The next update will take place
at the next period interval from the anchor time. For
example, for an anchor time at the top of a minute and a
period interval of a minute, the next update will be sent
at the top of the next minute.";
}
}
case on-change {
if-feature "on-change";
description
"The agent is requested to notify changes in values in the
datastore subset as defined by a filter.";
leaf dampening-period {
type yang:timeticks;
mandatory true;
description
"Minimum amount of time that needs to have passed since the
last time an update was provided for the subscription.";
}
}
}
}
grouping update-policy {
description
"This grouping describes the datastore specific subscription
conditions of a subscription.";
uses update-policy-modifiable {
augment "update-trigger/on-change" {
description
"Includes objects not modifiable once subscription is
established.";
leaf no-synch-on-start {
type empty;
description
"This leaf acts as a flag that determines behavior at the
start of the subscription. When present, synchronization
of state at the beginning of the subscription is outside
the scope of the subscription. Only updates about changes
that are observed from the start time, i.e. only push-
change-update notifications are sent. When absent (default
behavior), in order to facilitate a receiver's
synchronization, a full update is sent when the
subscription starts using a push-update notification, just
like in the case of a periodic subscription. After that,
push-change-update notifications only are sent unless the
Publisher chooses to resynch the subscription again.";
}
leaf-list excluded-change {
type change-type;
description
"Use to restrict which changes trigger an update.
For example, if modify is excluded, only creation and
deletion of objects is reported.";
}
}
}
}
grouping update-qos {
description
"This grouping describes Quality of Service information
concerning a subscription. This information is passed to lower
layers for transport prioritization and treatment";
leaf dscp {
type inet:dscp;
default "0";
description
"The push update's IP packet transport priority. This is made
visible across network hops to receiver. The transport
priority is shared for all receivers of a given subscription.";
}
leaf weighting {
type uint8 {
range "0 .. 255";
}
description
"Relative weighting for a subscription. Allows an underlying
transport layer perform informed load balance allocations
between various subscriptions";
reference
"RFC-7540, section 5.3.2";
}
leaf dependency {
type sn:subscription-id;
description
"Provides the Subscription ID of a parent subscription which
has absolute priority should that parent have push updates
ready to egress the publisher. In other words, there should be
no streaming of objects from the current subscription if of
the parent has something ready to push.";
reference
"RFC-7540, section 5.3.1";
}
}
grouping update-error-hints {
description
"Allow return additional negotiation hints that apply
specifically to push updates.";
leaf period-hint {
type yang:timeticks;
description
"Returned when the requested time period is too short. This
hint can assert an viable period for both periodic push
cadence and on-change dampening.";
}
leaf error-path {
type string;
description
"Reference to a YANG path which is associated with the error
being returned.";
}
leaf object-count-estimate {
type uint32;
description
"If there are too many objects which could potentially be
returned by the filter, this identifies the estimate of the
number of objects which the filter would potentially pass.";
}
leaf object-count-limit {
type uint32;
description
"If there are too many objects which could be returned by the
filter, this identifies the upper limit of the publisher's
ability to service for this subscription.";
}
leaf kilobytes-estimate {
type uint32;
description
"If the returned information could be beyond the capacity of
the publisher, this would identify the data size which could
result from this filter.";
}
leaf kilobytes-limit {
type uint32;
description
"If the returned information would be beyond the capacity of
the publisher, this identifies the upper limit of the
publisher's ability to service for this subscription.";
}
}
/*
* DATA NODES
*/
augment "/sn:establish-subscription/sn:input" {
description
"This augmentation adds additional subscription parameters that
apply specifically to datastore updates to RPC input.";
uses update-policy;
uses update-qos;
}
augment "/sn:establish-subscription/sn:input/sn:target" {
description
"This augmentation adds the datastore as a valid parameter object
for the subscription to RPC input. This provides a target for
the filter.";
case datastore {
uses datastore-criteria;
}
}
augment "/sn:establish-subscription/sn:output/"+
"sn:result/sn:no-success" {
description
"This augmentation adds datastore specific error info
and hints to RPC output.";
uses update-error-hints;
}
augment "/sn:modify-subscription/sn:input" {
description
"This augmentation adds additional subscription parameters
specific to datastore updates.";
uses update-policy-modifiable;
}
augment "/sn:modify-subscription/sn:output/"+
"sn:result/sn:no-success" {
description
"This augmentation adds push datastore error info and hints to
RPC output.";
uses update-error-hints;
}
notification push-update {
description
"This notification contains a push update, containing data
subscribed to via a subscription. This notification is sent for
periodic updates, for a periodic subscription. It can also be
used for synchronization updates of an on-change subscription.
This notification shall only be sent to receivers of a
subscription; it does not constitute a general-purpose
notification.";
leaf subscription-id {
type sn:subscription-id;
mandatory true;
description
"This references the subscription because of which the
notification is sent.";
}
leaf time-of-update {
type yang:date-and-time;
description
"This leaf contains the time of the update.";
}
leaf updates-not-sent {
type empty;
description
"This is a flag which indicates that not all data nodes
subscribed to are included with this update. In other words,
the publisher has failed to fulfill its full subscription
obligations. This may lead to intermittent loss of
synchronization of data at the client. Synchronization at the
client can occur when the next push-update is received.";
}
anydata datastore-contents {
description
"This contains the updated data. It constitutes a snapshot
at the time-of-update of the set of data that has been
subscribed to. The format and syntax of the data
corresponds to the format and syntax of data that would be
returned in a corresponding get operation with the same
filter parameters applied.";
}
}
notification push-change-update {
if-feature "on-change";
description
"This notification contains an on-change push update. This
notification shall only be sent to the receivers of a
subscription; it does not constitute a general-purpose
notification.";
leaf subscription-id {
type sn:subscription-id;
mandatory true;
description
"This references the subscription because of which the
notification is sent.";
}
leaf time-of-update {
type yang:date-and-time;
description
"This leaf contains the time of the update, i.e. the time at
which the change was observed.";
}
leaf updates-not-sent {
type empty;
description
"This is a flag which indicates that not all changes which
have occurred since the last update are included with this
update. In other words, the publisher has failed to
fulfill its full subscription obligations, for example in
cases where it was not able to keep up with a change burst.
To facilitate synchronization, a publisher may subsequently
send a push-update containing a full snapshot of subscribed
data. Such a push-update might also be triggered by a
subscriber requesting an on-demand synchronization.";
}
anydata datastore-changes {
description
"This contains datastore contents that has changed since the
previous update, per the terms of the subscription. Changes
are encoded analogous to the syntax of a corresponding yang-
patch operation, i.e. a yang-patch operation applied to the
YANG datastore implied by the previous update to result in the
current state (and assuming yang-patch could also be applied
to operational data).";
}
}
augment "/sn:subscription-started" {
description
"This augmentation adds many yang datastore specific objects to
the notification that a subscription has started.";
uses update-policy;
uses update-qos;
}
augment "/sn:subscription-started/sn:target" {
description
"This augmentation allows the datastore to be included as part
of the notification that a subscription has started.";
case datastore {
uses datastore-criteria;
}
}
augment "/sn:subscription-modified" {
description
"This augmentation adds many yang datastore specific objects to
the notification that a subscription has been modified.";
uses update-policy;
uses update-qos;
}
augment "/sn:subscription-config/sn:subscription" {
description
"This augmentation adds many yang datastore specific objects
which can be configured as opposed to established via RPC.";
uses update-policy;
uses update-qos;
}
augment "/sn:subscription-config/sn:subscription/sn:target" {
description
"This augmentation adds the datastore to the filtering
criteria for a subscription.";
case datastore {
uses datastore-criteria;
}
}
augment "/sn:subscriptions/sn:subscription" {
yp:notifiable-on-change true;
description
"This augmentation adds many datastore specific objects to a
subscription.";
uses update-policy;
uses update-qos;
}
augment "/sn:subscriptions/sn:subscription/sn:target" {
description
"This augmentation allows the datastore to be displayed as part
of the filtering criteria for a subscription.";
case datastore {
uses datastore-criteria;
}
}
/* YANG Parser Pyang crashing on the following syntax below
deviation "/sn:subscriptions/sn:subscription/sn:receivers/"
+ "sn:receiver/sn:pushed-notifications" {
deviate add {
yp:notifiable-on-change false;
}
}
deviation "/sn:subscriptions/sn:subscription/sn:receivers/"
+ "sn:receiver/sn:excluded-notifications" {
deviate add {
yp:notifiable-on-change false;
}
}
YANG Parser Pyang crashing on the following syntax above */
}
<CODE ENDS>
All security considerations from [subscribe] are relevant for datastores. In addition there are specific security considerations for receviers defined in Section 3.8
If the access control permissions on subscribed YANG nodes change during the lifecycle of a subscription, a publisher MUST either transparently conform to the new access control permissions, or must terminate or restart the subscriptions so that new access control permissions are re-established.
The NETCONF Authorization Control Model SHOULD be used to restrict the delivery of YANG nodes for which the receiver has no access.
For their valuable comments, discussions, and feedback, we wish to acknowledge Tim Jenkins, Kent Watsen, Susan Hares, Yang Geng, Peipei Guo, Michael Scharf, Sharon Chisholm, and Guangying Zheng.
| [RFC6470] | Bierman, A., "Network Configuration Protocol (NETCONF) Base Notifications", RFC 6470, DOI 10.17487/RFC6470, February 2012. |
| [RFC6536] | Bierman, A. and M. Bjorklund, "Network Configuration Protocol (NETCONF) Access Control Model", RFC 6536, DOI 10.17487/RFC6536, March 2012. |
| [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. |
| [RFC7951] | Lhotka, L., "JSON Encoding of Data Modeled with YANG", RFC 7951, DOI 10.17487/RFC7951, August 2016. |
| [RFC8072] | Bierman, A., Bjorklund, M. and K. Watsen, "YANG Patch Media Type", RFC 8072, DOI 10.17487/RFC8072, February 2017. |
| [subscribe] | Voit, E., Clemm, A., Gonzalez Prieto, A., Tripathy, A. and E. Nilsen-Nygaard, "Custom Subscription to Event Notifications", Internet-Draft draft-ietf-netconf-subscribed-notifications-01, April 2017. |
There are other related drafts which are progressing in the NETCONF WG. This section details the relationship of this draft to those others.
The draft [subscribe] is the techical foundation around which the rest of the YANG push datastore specific mechanisms are layered.
The [netconf-notif] draft supports yang-push by defining NETCONF transport specifics. Included are:
The [http-notif] draft supports yang-push by defining transport specific guidance where some form of HTTP is used underneath. Included are:
The draft [notifications2] is not required to implement yang-push. Instead it defines data plane notification elements which improve the delivered experience. The following capabilities are specified:
These capabilities would be delivered by adding the drafts newly proposed header objects to the push-update and push-change-update notifications defined here. This draft is not yet adopted by the NETCONF WG.
The properties of Dynamic and Configured Subscriptions can be combined to enable deployment models where the Subscriber and Receiver are different. Such separation can be useful with some combination of:
To build a Proxy Subscription, first the necessary information must be signaled as part of the <establish-subscription>. Using this set of Subscriber provided information; the same process described within section 3 will be followed.
After a successful establishment, if the Subscriber wishes to track the state of Receiver subscriptions, it may choose to place a separate on-change Subscription into the "Subscriptions" subtree of the YANG Datastore on the Publisher.
Currently there are ongoing discussions to revise the concept of datastores, allowing for proper handling and distinction of intended versus applied configurations and extending the notion of a datastore to operational data. When finalized, the new concept may open up the possibility for new types of subscription filters, for example, targeting specific datastores and targeting (potentially) differences in datatrees across different datastores.
Likewise, it is conceivable that filters are defined that apply to metadata, such as data nodes for which metadata has been defined that meets a certain criteria.
Defining any such subscription filters at this point would be highly speculative in nature. However, it should be noted that corresponding extensions may be defined in future specifications. Any such extensions will be straightforward to accommodate by introducing a model that defines new filter types, and augmenting the new filter type into the subscription model.
Push updates may become fairly large and extend across multiple subsystems in a YANG-Push Server. As a result, it conceivable to not combine all updates into a single update message, but to split updates into multiple separate update messages. Such splitting could occur along multiple criteria: limiting the number of data nodes contained in a single update, grouping updates by subtree, grouping updates by internal subsystems (e.g., by line card), or grouping them by other criteria.
Splitting updates bears some resemblance to fragmenting packets. In effect, it can be seen as fragmenting update messages at an application level. However, from a transport perspective, splitting of update messages is not required as long as the transport does not impose a size limitation or provides its own fragmentation mechanism if needed. We assume this to be the case for YANG-Push. In the case of NETCONF, RESTCONF, HTTP/2, no limit on message size is imposed. In case of other transports, any message size limitations need to be handled by the corresponding transport mapping.
There may be some scenarios in which splitting updates might still make sense. For example, if updates are collected from multiple independent subsystems, those updates could be sent separately without need for combining. However, if updates were to be split, other issues arise. Examples include indicating the number of updates to the receiver, distinguishing a missed fragment from a missed update, and the ordering with which updates are received. Proper addressing those issues would result in considerable complexity, while resulting in only very limited gains. In addition, if a subscription is found to result in updates that are too large, a publisher can always reject the request for a subscription while the subscriber is always free to break a subscription up into multiple subscriptions.
A possible is the introduction of an additional parameter "changes-only" for periodic subscription. Including this flag would results in sending at the end of each period an update containing only changes since the last update (i.e. a change-update as in the case of an on-change subscription), not a full snapshot of the subscribed information. Such an option might be interesting in case of data that is largely static and bandwidth-constrained environments.
(To be removed by RFC editor prior to publication)
Issue #6: Data plane notifications and layered headers. Specifically how do we want to enable standard header unification and bundle support vs. the data plane notifications currently defined.
(To be removed by RFC editor prior to publication)
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