Internet DRAFT - draft-voit-restconf-yang-push
draft-voit-restconf-yang-push
NETCONF E. Voit
Internet-Draft A. Clemm
Intended status: Informational A. Tripathy
Expires: April 15, 2016 E. Nilsen-Nygaard
A. Gonzalez Prieto
Cisco Systems
October 13, 2015
Restconf subscription and HTTP push for YANG datastores
draft-voit-restconf-yang-push-00
Abstract
This document defines Restconf subscription and push mechanisms to
continuously stream information from YANG datastores over HTTP.
These mechanisms allow client applications or operations support
systems to request custom sets of updates from a YANG datastore.
This document also specifies how to stream updates over HTTP without
Restconf. In either case, updates are pushed by a datastore to a
receiver per a subscription policy, without requiring continuous
requests.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 15, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Subscription Model . . . . . . . . . . . . . . . . . . . 4
3.2. Subscription states at Publisher . . . . . . . . . . . . 5
3.3. Mechanisms for Subscription Establishment and Maintenance 6
3.4. Negotiation of Subscription Policies . . . . . . . . . . 8
3.5. Support for Periodic and On-change . . . . . . . . . . . 8
3.6. Filters and Streams . . . . . . . . . . . . . . . . . . . 9
3.7. Authorization . . . . . . . . . . . . . . . . . . . . . . 9
3.8. Subscription Multiplexing . . . . . . . . . . . . . . . . 9
3.9. Push Data Stream and Transport Mapping . . . . . . . . . 10
3.10. YANG Tree . . . . . . . . . . . . . . . . . . . . . . . . 14
4. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 15
5. Security Considerations . . . . . . . . . . . . . . . . . . . 18
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.1. Normative References . . . . . . . . . . . . . . . . . . 18
6.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Dynamic YANG Subscription when the Subscriber and
Receiver are different . . . . . . . . . . . . . . . 20
Appendix B. End-to-End Deployment Guidance . . . . . . . . . . . 21
B.1. Call Home . . . . . . . . . . . . . . . . . . . . . . . . 21
B.2. TLS Heartbeat . . . . . . . . . . . . . . . . . . . . . . 21
B.3. Putting it together . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
Requirements for subscriptions to YANG datastores are defined in
[pub-sub-reqs]. Mechanisms to support YANG subscriptions and
datastore object push over a NETCONF are defined in
[netconf-yang-push]. Restconf support of subscriptions, with HTTP
transport of pushed updates is also needed by the market. This
document provides such a specification.
Key benefits of pushing data via HTTP include:
o Ability to configure static subscriptions on a Publisher
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o Ability for the Publisher to initiate communications with the
Receiver
o Ability of a Subscriber to be different from the Receiver
There are also additional benefits which can be realized when pushing
updates via HTTP/2 [RFC7540]:
o Subscription multiplexing over independent HTTP/2 streams
o Stream prioritization
o Stream dependencies
o Flow control on independent streams
o Header compression
These additional benefits will address issues resulting from head-of-
line blocking and relative subscription priority.
To maximize transport independence of YANG subscription methods, this
document reuses many capabilities of [netconf-yang-push][] including:
o Operations for creating, modifying and deleting subscriptions
o Syntax and parameters for negotiating the subscription
o YANG data model to manage subscriptions
o Mechanisms to communicate subscription filters and data streams
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Datastore: a conceptual store of instantiated management information,
with individual data items represented by data nodes which are
arranged in hierarchical manner.
Dynamic YANG Subscription: Subscription negotiated with Publisher via
create, modify, and delete control plane signaling messages.
Publisher: an entity responsible for distributing subscribed YANG
object data per the terms of a Subscription. In general, a Publisher
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is the owner of the YANG datastore that is subjected to the
Subscription.
Receiver: the target where a Publisher pushes updates. In many
deployments, the Receiver and Subscriber will be the same entity.
Static YANG Subscription: A Subscription installed via a
configuration interface.
Subscriber: An entity able to request and negotiate a contract for
push updates from a Publisher.
Subscription: A contract between a Subscriber and a Publisher,
stipulating which information the Receiver wishes to have pushed from
the Publisher without the need for further solicitation.
Subscription Update: Set of data nodes and object values pushed
together as a unit and intended to meet the obligations of a single
subscription at a snapshot in time.
3. Solution
This document specifies mechanisms that allow subscribed information
updates to be pushed from a YANG datastore. Subscriptions may either
be initiated via requests by Subscribers, or statically configured on
a Publisher. As in [netconf-yang-push], Publisher must respond to a
subscription request explicitly positively or negatively. Negative
responses will include information about why the Subscription was not
accepted, in order to facilitate converging on an acceptable set of
Subscription parameters.
Once a Subscription has been established, updates are pushed to the
Receiver until the Subscription terminates. Based on parameters
within the Subscription, these updates can be streamed immediately as
any subscribed objects change, or sent periodically.
3.1. Subscription Model
Subscriptions use the base data model from [netconf-yang-push]. This
model is extended with several optional parameters for Subscription
Priority and Subscription Dependency. These parameters allow a
Subscriber or other configuration interface to assert how it prefers
the Publisher allocate resources when handling multiple
Subscriptions. These parameters are intended to be used in
conjunction with the transport layer. Specifically, when a new
Subscription is being established with an underlying transport is
HTTP/2, these parameters may be directly mapped into HTTP/2 to
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prioritize transport and to assist with flow control of individual
streams.
3.2. Subscription states at Publisher
Below is the state machine for the Publisher. It is important to
note that a Subscription doesn't exist at the Publisher until it is
accepted and made active. The assertion of a <create-subscription>
by a Subscriber is insufficient for that asserted subscription to be
externally visible via this state machine.
Subscription states at Publisher
.-------.
| start |
'-------'
|
create
|
| .----------modify-------------.
v v '
.-----------. .-----------.
.--------. | |------>suspend------->| |
modify '| active | | suspended |
'--------->| |<----reactivate<------| |
'-----------' '-----------'
| |
delete delete
| |
v |
.-------. |
| end |<-----------------------------'
'-------'
Of interest in this state machine are the following:
o Successful <create-subscription> or <modify-subscription> actions
must put the subscription into an active state.
o Failed <modify-subscription> actions will leave the subscription
in its previous state, with no visible change to any streaming
updates.
o A <delete-subscription> action will delete the entire
subscription.
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3.3. Mechanisms for Subscription Establishment and Maintenance
On a Publisher, it must be possible to instantiate a Subscription via
dynamic Subscriber signaling, as well as via Static configuration.
Dynamic YANG Subscriptions are signaled Subscriptions aimed at the
running datastore and are unable to impact the startup configuration.
They should always terminate when there is loss of transport session
connectivity between the Publisher and Receiver.
Static Subscriptions are applied via an operations interface to the
startup and running configurations. Loss or non-availability of
transport session connectivity will place the Subscription into the
suspended state. Logic beyond the scope of this specification will
dictate when any particular Subscription should be reactivated.
There are three models for Subscription establishment and
maintenance:
1. Dynamic YANG Subscription: Subscriber and Receiver are the same
2. Static YANG Subscription
3. Dynamic YANG Subscription: Subscriber and Receiver are different
The first two are described in this section. The third is described
in Appendix A. This third option can be moved into the body of this
specification should the IETF community desire. In theory, all three
models may be intermixed in a single deployment. Figure 2 shows such
a scenario.
.---------------.
| Publisher |
'---------------'
^ ^ | ^
| | | |
.-----Restconf----' | | '-----Restconf----.
| .-----' '-HTTP-. |
V | V |
.-------------. .------------. .----------. .------------.
| Subscriber+ | | Operations | | Receiver | | Subscriber |
| Receiver | | /Config | '----------' '------------'
'-------------' '------------' ^ ^ ^
^ (out of scope) : : :
: ^ : :....Model 3....:
Model 1 :...Model 2...: (out of scope)
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3.3.1. Dynamic YANG Subscription: Subscriber and Receiver are the same
With all Dynamic YANG Subscriptions, as with [netconf-yang-push] it
must be possible to configure and manage Subscriptions via signaling.
This signaling is transported over [restconf]. Once established,
streaming Subscription Updates are then delivered via Restconf SSE.
3.3.2. Static YANG Subscription
With a Static YANG Subscription, all information needed to establish
a secure object push relationship with that Receiver must be
configured via a configuration interface on the Publisher. This
information includes all the <create-subscription> information
identified in section 3.3.1. This information also includes the
Receiver address, encoding selection, and any security credentials
required to establish TLS between the Publisher and Receiver.
Mechanisms for locally configuring these parameters are outside the
scope of this document.
With this information, the Publisher will establish a secure
transport connection with the Receiver and then begin pushing the
streaming updates to the Receiver. Since Restconf might not exist on
the Receiver, it is not desirable to require that updates be pushed
via Restconf. In place of Restconf, a TLS secured HTTP Client
connection must be established with an HTTP Server located on the
Receiver. Subscription Updates will then be sent via HTTP Post
messages to the Receiver.
Post messages will be addressed to HTTP augmentation code on the
Receiver capable accepting and responding to Subscription Updates.
At least the initial Post message must include the URI for the
subscribed resource. This URI can be retained for future use by the
Receiver.
After successful receipt of an initial Subscription Update for a
particular Subscription, this augmentation should reply back with an
HTTP status code of 201 (Created). Further successful receipts
should result in the return of code of 202 (Accepted). At any point,
receipt of any status codes from 300-510 with the exception of 408
(Request Timeout) should result in the movement of the Subscription
to the suspended state. A sequential series of multiple 408
exceptions should also drive the Subscription to a suspended state.
Security on an HTTP client/Publisher can be strengthened by only
accepting Response code feedback for recently initiated HTTP POSTs.
Figure 3 depicts this message flow.
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+-----------+ +----------+
| Publisher | | Receiver |
+-----------+ +----------+
|<--------------TLS------------>|
| |
|HTTP POST (Sub ID, URI, data1) |
|------------------------------>|
| HTTP 201 (Created)|
|<------------------------------|
|HTTP POST (Sub ID, data2) |
|------------------------------>|
| HTTP 200 or 202 (Accepted)|
|<------------------------------|
| data3 |
|<----------------------------->|
If HTTP/2 transport is available to a Receiver, the Publisher should
also:
o point individual Subscription Updates to a unique HTTP/2 stream
for that Subscription,
o take any subscription-priority and provision it into the HTTP/2
stream priority, and
o take any subscription-dependency and provision it into the HTTP/2
stream dependency.
3.4. Negotiation of Subscription Policies
When using signaling to create a Dynamic YANG Subscription,
negotiable parameters will include the same negotiable parameters
defined within [netconf-yang-push].
Additionally, negotiation may also include Subscription Priority. A
Publisher may accept a Subscriber asserted Priority, as well as
rejecting a subscription with a hint at what priority might be
accepted.
3.5. Support for Periodic and On-change
Implementations must support periodic and/or on-change subscriptions
as defined in [netconf-yang-push].
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3.6. Filters and Streams
Implementations must support filters and streams as defined in
[netconf-yang-push].
3.7. Authorization
Same authorization model for data as [netconf-yang-push] will be
used. This includes functions of the Netconf Access Control Model
[RFC6536] applied to objects to be pushed via Restconf.
A Subscription (including a Static YANG Subscription) may only be
established if the Subscriber or some entity statically configuring
via the Publisher's operational interface has read access to the
target data node.
3.8. Subscription Multiplexing
When pushed directly over HTTP/2, it is expected that each
Subscription Update will be allocated a separate Stream. The will
enable multiplexing, and address issues of Head-of-line blocking with
different priority Subscriptions.
When pushed via Restconf over HTTP/2, different Subscriptions will
not be mapped to independent HTTP/2 streams. When Restconf specifies
this mapping, it should be integrated into this specification.
Even without HTTP/2 multiplexing, it is possible that updates might
be delivered in a different sequence than generated. Reasons for
this might include (but are not limited to):
o different durations needed to create various Subscription Updates,
o marshalling and bundling of multiple Subscription Updates for
transport, and
o parallel HTTP1.1 sessions
Therefore each Subscription Update will include a microsecond level
timestamp to ensure that a receiver understands the time when a that
update was generated. Use of this timestamp can give an indication
of the state of objects at a Publisher when state-entangled
information is received across different subscriptions. The use of
the latest Subscription Update timestamp for a particular object
update can introduce errors. So when state-entangled updates have
inconsistent object values and temporally close timestamps, a
Receiver might consider performing a 'get' to validate the current
state of objects.
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3.9. Push Data Stream and Transport Mapping
Transported updates will contain data for one or more Subscription
Updates. Each transported Subscription Update notification contains
several parameters:
o A global subscription ID correlator, referencing the name of the
Subscription on whose behalf the notification is sent.
o Data nodes containing a representation of the datastore subtree
containing the updates. The set of data nodes must be filtered
per access control rules to contain only data that the subscriber
is authorized to see.
o An event time which contains the time stamp at publisher when the
event is generated.
3.9.1. Pushing Subscription Updates via Restconf
Subscribers can dynamically learn whether a RESTCONF server supports
yang-push. This is done by issuing an HTTP request OPTIONS, HEAD, or
GET on the stream push-update. E.g.:
GET /restconf/data/ietf-restconf-monitoring:restconf-state/
streams/stream=yang-push HTTP/1.1
Host: example.com
Accept: application/yang.data+xml
If the server supports it, it may respond
HTTP/1.1 200 OK
Content-Type: application/yang.api+xml
<stream xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring">
<name>yang-push</name>
<description>Yang push stream</description>
<access>
<encoding>xml</encoding>
<location>https://example.com/streams/yang-push-xml
</location>
</access>
<access>
<encoding>json</encoding>
<location>https://example.com/streams/yang-push-json
</location>
</access>
</stream>
If the server does not support yang push, it may respond
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HTTP/1.1 404 Not Found
Date: Mon, 25 Apr 2012 11:10:30 GMT
Server: example-server
Subscribers can determine the URL to receive updates by sending an
HTTP GET request for the "location" leaf with the stream list entry.
The stream to use for yang push is the push-update stream. The
location returned by the publisher can be used for the actual
notification subscription. Note that different encodings are
supporting using different locations. For example, he subscriber
might send the following request:
GET /restconf/data/ietf-restconf-monitoring:restconf-state/
streams/stream=yang-push/access=xml/location HTTP/1.1
Host: example.com
Accept: application/yang.data+xml
The publisher might send the following response:
HTTP/1.1 200 OK
Content-Type: application/yang.api+xml
<location
xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring">
https://example.com/streams/yang-push-xml
</location>
To subscribe and start receiving updates, the subscriber can then
send an HTTP GET request for the URL returned by the publisher in the
request above. The accept header must be "text/event -stream". The
publisher handles the connection as an event stream, using the Server
Sent Events[W3C-20121211] transport strategy.
The publisher MUST support as query parameters for a GET method on
this resource all the parameters of a subscription. The only
exception is the encoding, which is embedded in the URI. An example
of this is:
// subtree filter = /foo
// periodic updates, every 5 seconds
GET /mystreams/yang-push?subscription-id=my-sub&period=5&
xpath-filter=%2Fex:foo[starts-with("bar"."some"]
Should the publisher not support the requested subscription, it may
reply:
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HTTP/1.1 501 Not Implemented
Date: Mon, 23 Apr 2012 17:11:00 GMT
Server: example-server
Content-Type: application/yang.errors+xml
<errors xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
<error>
<error-type>application</error-type>
<error-tag>operation-not-supported</error-tag>
<error-severity>error</error-severity>
<error-message>Xpath filters not supported</error-message>
<error-info>
<supported-subscription xmlns="urn:ietf:params:xml:ns:
netconf:datastore-push:1.0">
<subtree-filter/>
</supported-subscription>
</error-info>
</error>
</errors>
with an equivalent JSON encoding representation of:
HTTP/1.1 501 Not Implemented
Date: Mon, 23 Apr 2012 17:11:00 GMT
Server: example-server
Content-Type: application/yang.errors+json
{
"ietf-restconf:errors": {
"error": {
"error-type": "protocol",
"error-tag": "operation-not-supported",
"error-message": "Xpath filters not supported."
"error-info": {
"datastore-push:supported-subscription": {
"subtree-filter": [null]
}
}
}
}
}
The following is an example of a push Subscription Update data for
the subscription above. It contains a subtree with root foo that
contains a leaf called bar:
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XML encoding representation:
<?xml version="1.0" encoding="UTF-8"?>
<notification xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
<subscription-id xmlns="urn:ietf:params:xml:ns:restconf:
datastore-push:1.0">
my-sub
</subscription-id>
<eventTime>2015-03-09T19:14:56Z</eventTime>
<datastore-contents xmlns="urn:ietf:params:xml:ns:restconf:
datastore-push:1.0">
<foo xmlns="http://example.com/yang-push/1.0">
<bar>some_string</bar>
</foo>
</datastore-contents>
</notification>
Or with the equivalent YANG over JSON encoding representation as
defined in[yang-json] :
{
"ietf-restconf:notification": {
"datastore-push:subscription-id": "my-sub",
"eventTime": "2015-03-09T19:14:56Z",
"datastore-push:datastore-contents": {
"example-mod:foo": { "bar": "some_string" }
}
}
}
To modify a subscription, the subscriber issues another GET request
on the provided URI using the same subscription-id as in the original
request. For example, to modify the update period to 10 seconds, the
subscriber may send:
GET /mystreams/yang-push?subscription-id=my-sub&period=10&
subtree-filter=%2Ffoo'
To delete a subscription, the subscriber issues a DELETE request on
the provided URI using the same subscription-id as in the original
request
DELETE /mystreams/yang-push?subscription-id=my-sub
3.9.2. Pushing Subscription Updates directly via HTTP
For any version of HTTP, the basic encoding will look as below is the
above JSON representation wrapped in an HTTP header. Mechanism will
be
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POST (IP+Port) HTTP/1.1
From: (Identifier for Network Element)
User-Agent: (CiscoYANGPubSub/1.0)
Content-Type: multipart/form-data
Content-Length: (determined runtime)
{
"ietf-yangpush:notification": {
"datastore-push:subscription-id": "my-sub",
"eventTime": "2015-03-09T19:14:56Z",
"datastore-push:datastore-contents": {
"foo": { "bar": "some_string" }
}
}
}
3.10. YANG Tree
Below is the object tree for the model. All items are imported from
[netconf-yang-push] except for the addition of "subscription-
priority" and "subscription-dependency".
module: ietf-restconf-yang-push
+-ro system-streams
| +-ro system-stream* system-stream
+-rw filters
| +-rw filter* [filter-id]
| +-rw filter-id filter-id
| +-rw subtree-filter? subtree-filter
| +-rw xpath-filter? yang:xpath1.0
+-rw subscription-config
| +-rw datastore-push-subscription* [subscription-id]
| +--rw datastore-push-subscription* [subscription-id]
| +--rw subscription-id subscription-id
| +--rw target-datastore? datastore
| +--rw stream? system-stream
| +--rw encoding? encoding
| +--rw start-time? yang:date-and-time
| +--rw stop-time? yang:date-and-time
| +--rw (update-trigger)?
| | +--:(periodic)
| | | +--rw period? yang:timeticks
| | +--:(on-change)
| | +--rw no-synch-on-start? empty
| | +--rw dampening-period yang:timeticks
| | +--rw excluded-change* change-type
| +--rw (filterspec)?
| | +--:(inline)
| | | +--rw subtree-filter? subtree-filter
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| | | +--rw xpath-filter? yang:xpath1.0
| | +--:(by-reference)
| | +--rw filter-ref? filter-ref
| +--rw receiver-address
| | +-rw (push-base-transport)?
| | +-:(tcpudp)
| | +-rw tcpudp
| | +-rw address? inet:host
| | +-rw port? inet:port-number
| +--rw subscription-priority? uint8
| +--rw subscription-dependency? string
+-ro subscriptions
+--ro datastore-push-subscription* [subscription-id]
+--ro subscription-id subscription-id
+--ro configured-subscription? empty
+--ro subscription-status? identityref
+--ro target-datastore? datastore
+--ro stream? system-stream
+--ro encoding? encoding
+--ro start-time? yang:date-and-time
+--ro stop-time? yang:date-and-time
+--ro (update-trigger)?
| +--:(periodic)
| | +--ro period? yang:timeticks
| +--:(on-change)
| +--ro no-synch-on-start? empty
| +--ro dampening-period yang:timeticks
| +--ro excluded-change* change-type
+--ro (filterspec)?
| +--:(inline)
| | +--ro subtree-filter? subtree-filter
| | +--ro xpath-filter? yang:xpath1.0
| +--:(by-reference)
| +--ro filter-ref? filter-ref
+--ro receiver-address
| +--ro (push-base-transport)?
| +--:(tcpudp)
| +--ro tcpudp
| +--ro address? inet:host
| +--ro port? inet:port-number
+--rw subscription-priority? uint8
+--rw subscription-dependency? string
4. YANG Module
namespace "urn:ietf:params:xml:ns:yang:ietf-restconf-push";
prefix "rc-push";
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import ietf-datastore-push {
prefix ds-push;
}
organization
"IETF NETCONF (Network Configuration) Working Group";
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: Eric Voit
<mailto:evoit@cisco.com>
Editor: Alexander Clemm
<mailto:alex@cisco.com>
Editor: Ambika Prasad Tripathy
<mailto:ambtripa@cisco.com>
Editor: Einar Nilsen-Nygaard
<mailto:einarnn@cisco.com>
Editor: Alberto Gonzalez Prieto
<mailto:albertgo@cisco.com>";
description
"This module contains conceptual YANG specifications for
Restconf datastore push.";
revision 2015-10-01 {
description
"Initial revision.";
reference "restconf YANG Datastore push";
}
grouping subscription-qos {
description
"This grouping describes Quality of Service information
concerning a subscription. This information is passed to lower
layers for transport priortization and treatment";
leaf subscription-priority {
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type uint8;
description
"Relative priority for a subscription. Allows an underlying
transport layer perform informed load balance allocations
between various subscriptions";
}
leaf subscription-dependency {
type string;
description
"Provides the Subscription ID of a parent subscription
without which this subscription should not exist. In
other words, there is no reason to stream these objects
if another subscription is missing.";
}
}
augment "/ds-push:subscription-config/" +
"ds-push:datastore-push-subscription" {
description
"Aguments configured subscriptions with QoS parameters.";
uses subscription-qos;
}
augment "/ds-push:subscriptions/" +
"ds-push:datastore-push-subscription" {
description
"Aguments the list of currently active subscriptions
with QoS parameters.";
uses subscription-qos;
}
augment "/ds-push:create-subscription/" +
"ds-push:input" {
description
"Aguments the create subscription rpc with QoS parameters.";
uses subscription-qos;
}
augment "/ds-push:modify-subscription/" +
"ds-push:input" {
description
"Aguments the modify subscription rpc with QoS parameters.";
uses subscription-qos;
}
}
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5. Security Considerations
Subscriptions could be used to intentionally or accidentally overload
resources of a Publisher. For this reason, it is important that the
Publisher has the ability to prioritize the establishment and push of
updates where there might be resource exhaust potential. In
addition, a server needs to be able to suspend existing subscriptions
when needed. When this occurs, the subscription status must be
updated accordingly and the clients are notified.
A Subscription could be used to retrieve data in subtrees that a
client has not authorized access to. Therefore it is important that
data pushed via a Subscription is authorized equivalently with
regular data retrieval operations. Data being pushed to a client
needs therefore to be filtered accordingly, just like if the data
were being retrieved on-demand. The Netconf Authorization Control
Model [RFC6536] applies.
One or more Publishers could be used to overwhelm a Receiver which
doesn't even support subscriptions. Therefore Updates MUST only be
transmittable over Encrypted transports. Clients which do not want
pushed data need only terminate or refuse any transport sessions from
the Publisher.
One or more Publishers could overwhelm a Receiver which is unable to
control or handle the volume of Updates received. In deployments
where this might be a concern, transports supporting per-subscription
Flow Control and Prioritization (such as HTTP/2) should be selected.
Another benefit is that a well-behaved Publisher implementation is
that it is difficult to a Publisher to perform a DoS attack on a
Receiver. DoS attack protection comes from:
o the requirement for trust of a TLS session before publication,
o the need for an HTTP transport augmentation on the Receiver, and
o that the Publication process is suspended when the Receiver
doesn't respond.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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[RFC6520] Seggelmann, R., Tuexen, M., and M. Williams, "Transport
Layer Security (TLS) and Datagram Transport Layer Security
(DTLS) Heartbeat Extension", RFC 6520, DOI 10.17487/
RFC6520, February 2012,
<http://www.rfc-editor.org/info/rfc6520>.
[RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration
Protocol (NETCONF) Access Control Model", RFC 6536, DOI
10.17487/RFC6536, March 2012,
<http://www.rfc-editor.org/info/rfc6536>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI
10.17487/RFC7540, May 2015,
<http://www.rfc-editor.org/info/rfc7540>.
6.2. Informative References
[call-home]
Watsen, K., "NETCONF Call Home and RESTCONF Call Home",
July 2015, <https://tools.ietf.org/html/draft-ietf-
netconf-call-home-09>.
[netconf-yang-push]
Clemm, Alexander., Gonzalez Prieto, Alberto., and Eric.
Voit, "Subscribing to YANG datastore push updates",
October 2015, <https://datatracker.ietf.org/doc/draft-
clemm-netconf-yang-push/>.
[pub-sub-reqs]
Voit, Eric., Clemm, Alexander., and Alberto. Gonzalez
Prieto, "Subscribing to datastore push updates", October
2015, <https://datatracker.ietf.org/doc/draft-ietf-i2rs-
pub-sub-requirements/>.
[restconf]
Bierman, Andy., Bjorklund, Martin., and Kent. Watsen,
"RESTCONF Protocol", July 2015,
<https://datatracker.ietf.org/doc/draft-ietf-netconf-
restconf/>.
[W3C-20121211]
"Server-Sent Events, World Wide Web Consortium CR CR-
eventsource-20121211", December 2012,
<http://www.w3.org/TR/2012/CR-eventsource-20121211>.
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[yang-json]
Lhotka, Ladislav., "JSON Encoding of Data Modeled with
YANG", October 2015, <https://datatracker.ietf.org/doc/
draft-ietf-netmod-yang-json/>.
Appendix A. Dynamic YANG Subscription when the Subscriber and Receiver
are different
The methods of Sections 3.3.1 and 3.3.2 can be combined to enable
deployment models where the Subscriber and Receiver are different.
Such separation can be useful with some combination of:
o An operator wants any Subscriptions immediately deleted should TLS
connectivity be lost. (I.e., Subscriptions don't default into a
'Suspended' state on the Publisher.)
o An operator wants the Publisher to include highly restrictive
capacity management and security mechanisms outside of domain of
existing operational or programmatic interfaces.
o Restconf is not desired on the Receiver.
o The Publisher doesn't want to maintain Restconf subscriptions with
many Receivers.
To do this, first the necessary information must be signaled as part
of the <create-subscription>. This includes all the information
described in section 3.3.2, with the exception of the security
credentials. (It is assumed that any security credentials required
for establishing any transport connections are pre-provisioned on all
devices.)
Using this set of Subscriber provided information, the same process
described within section 3.3.2 will be followed. There is one
exception. When an HTTP status code is 201 is received by the
Publisher, it will inform the Subscriber of Subscription
establishment success via its Restconf connection.
After successful establishment, if the Subscriber wishes to maintain
the state of Receiver subscriptions, it can simply place a separate
on-change Subscription into the "Subscriptions" subtree of the YANG
Datastore on the Publisher.
Putting it all together, the message flow is:
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+------------+ +-----------+ +----------+
| Subscriber | | Publisher | | Receiver |
+------------+ +-----------+ +----------+
| Restconf PUT: | |
| <create-subscription>| |
|--------------------->| |
| | |
| |<-----------TLS------------>|
| | |
| |HTTP POST (Sub ID, data1, |
| |(stream ID, URI?)) |
| |--------------------------->|
| | HTTP 201 (Created)|
| |<---------------------------|
| Success: HTTP 204| |
|<---------------------| |
| |HTTP POST (Sub ID, data2) |
| |--------------------------->|
| | HTTP 200 or 202 (Accepted)|
| |<---------------------------|
| | data3 |
| |<-------------------------->|
| | |
Appendix B. End-to-End Deployment Guidance
Several technologies are expected to be seen within a deployment to
achieve security and ease-of-use requirements. These are not
necessary for an implementation of this specification, but will be
useful to consider when considering the operational context.
B.1. Call Home
Pub/Sub implementations should have the ability to transparently
incorporate lower layer technologies such as Call Home so that secure
TLS connections are always originated from the Publisher. There is a
Restconf Call home function in [call-home]. For security reasons,
this should be implemented as desired.
B.2. TLS Heartbeat
Unlike NETCONF, HTTP sessions might not quickly allow a Subscriber to
recognize when the communication path has been lost from the
Publisher. To recognize this, it is possible for a Receiver (usually
the subscriber) to establish a TLS heartbeat [RFC6520]. In the case
where a TLS heartbeat is included, it should be sent just from
Receiver to Publisher. Loss of the heartbeat should result in the
Subscription being terminated with the Subscriber (even when the
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Subscriber and Receiver are different). The Subscriber can then
attempt to re-establish the subscription if desired. If the
Subscription remains active on the Publisher, future receipt of
objects associated with that (or any other unknown) subscription ID
should result in a <delete-subscription> being returned to the
Publisher from the Receiver.
B.3. Putting it together
If Subscriber and receiver are same entity then subscriber can direct
send create_subscription message to publisher. Once the subscription
moved to accepted state, the receiver can use Server Sent Events
[W3C-20121211] transport strategy to subscriber event notifications
for the data as defined in[restconf].
Authors' Addresses
Eric Voit
Cisco Systems
Email: evoit@cisco.com
Alexander Clemm
Cisco Systems
Email: alex@cisco.com
Ambika Prasad Tripathy
Cisco Systems
Email: ambtripa@cisco.com
Einar Nilsen-Nygaard
Cisco Systems
Email: einarnn@cisco.com
Alberto Gonzalez Prieto
Cisco Systems
Email: albertgo@cisco.com
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