Network Working Group                                          R. Murray
Internet-Draft                                          B. Niven-Jenkins
Intended status: Standards Track                Velocix (Alcatel-Lucent)
Expires: March 7, July 2, 2015                                 September 3,                                  December 29, 2014

                   CDNI Control Interface / Triggers
                  draft-ietf-cdni-control-triggers-04
                  draft-ietf-cdni-control-triggers-05

Abstract

   This document describes the part of the CDN Interconnection Control
   Interface that allows a CDN to trigger activity in an interconnected
   CDN that is configured to deliver content on its behalf.  The
   upstream CDN can use this mechanism to request that the downstream
   CDN pre-positions metadata or content, or that it invalidates or
   purges metadata or content.  The upstream CDN can monitor the status
   of activity that it has triggered in the downstream CDN.

Requirements Language

   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].

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 March 7, July 2, 2015.

Copyright Notice

   Copyright (c) 2014 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
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Model for CDNI Triggers . . . . . . . . . . . . . . . . . . .   4
     2.1.  Timing of Triggered Activity  . . . . . . . . . . . . . .   6
     2.2.  Scope of Triggered Activity . . . . . . . . . . . . . . .   6
     2.3.  Trigger Results . . . . . . . . . . . . . . . . . . . . .   6
   3.  Collections of Trigger Status Resources . . . . . . . . . . .   6   7
   4.  CDNI Trigger Interface  . . . . . . . . . . . . . . . . . . .   7   8
     4.1.  Creating Triggers . . . . . . . . . . . . . . . . . . . .   8   9
     4.2.  Checking Status . . . . . . . . . . . . . . . . . . . . .  10
       4.2.1.  Polling Trigger Status Resource collections . . . . .  10
       4.2.2.  Polling Trigger Status Resources  . . . . . . . . . .  10  11
     4.3.  Cancelling Triggers . . . . . . . . . . . . . . . . . . .  10  11
     4.4.  Deleting Triggers . . . . . . . . . . . . . . . . . . . .  11  12
     4.5.  Expiry of Trigger Status Resources  . . . . . . . . . . .  12
     4.6.  Loop Detection and Prevention . . . . . . . . . . . . . .  12  13
     4.7.  Error Handling  . . . . . . . . . . . . . . . . . . . . .  13
     4.8.  Content URLs  . . . . . . . . . . . . . . . . . . . . . .  13  14
   5.  CI/T Object Properties and Encoding . . . . . . . . . . . . .  14  15
     5.1.  CI/T Objects  . . . . . . . . . . . . . . . . . . . . . .  14  15
       5.1.1.  CI/T Commands . . . . . . . . . . . . . . . . . . . .  14  15
       5.1.2.  Trigger Status Resource . . . . . . . . . . . . . . .  15  16
       5.1.3.  Trigger Collection  . . . . . . . . . . . . . . . . .  16  17
     5.2.  Properties of CI/T Objects  . . . . . . . . . . . . . . .  17  18
       5.2.1.  Trigger Specification . . . . . . . . . . . . . . . .  18
       5.2.2.  Trigger Type  . . . . . . . . . . . . . . . . . . . .  19  20
       5.2.3.  Trigger Status  . . . . . . . . . . . . . . . . . . .  19  20
       5.2.4.  PatternMatch  . . . . . . . . . . . . . . . . . . . .  20  21
       5.2.5.  Absolute Time . . . . . . . . . . . . . . . . . . . .  21  22
       5.2.6.  Error Description . . . . . . . . . . . . . . . . . .  21  22
       5.2.7.  Error Code  . . . . . . . . . . . . . . . . . . . . .  22  23
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  22  23
     6.1.  Creating Triggers . . . . . . . . . . . . . . . . . . . .  23  24
       6.1.1.  Preposition . . . . . . . . . . . . . . . . . . . . .  23  24
       6.1.2.  Invalidate  . . . . . . . . . . . . . . . . . . . . .  24  25
     6.2.  Examining Trigger Status  . . . . . . . . . . . . . . . .  25  26
       6.2.1.  Collection of All Triggers  . . . . . . . . . . . . .  25  26
       6.2.2.  Filtered Collections of Triggers  . . . . . . . . Trigger Status Resources  . .  26  27
       6.2.3.  Individual Trigger Status Resources . . . . . . . . . . . . . .  28  29
       6.2.4.  Polling for Change  . . . . . . . . . . . . . . . . .  30  31
       6.2.5.  Removing a  Deleting Trigger Status Resources . . . . . . . . . . . . . . . . .  33  34
       6.2.6.  Error Reporting . . . . . . . . . . . . . . . . . . .  35
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  36
     7.1.  Media type registrations  . . . . . . . . . . . . . . . .  36  37
       7.1.1.  CI/T Commands . . . . . . . . . . . . . . . . . . . .  36  37
       7.1.2.  CI/T Trigger Status Resource  . . . . . . . . . . . .  37  38
       7.1.3.  CI/T Trigger Collection . . . . . . . . . . . . . . .  38  39
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  39  40
     8.1.  Authentication, Confidentiality, Integrity Protection . .  39  40
     8.2.  Denial of Service . . . . . . . . . . . . . . . . . . . .  39  40
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  40  41
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  40  41
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  40  41
     10.2.  Informative References . . . . . . . . . . . . . . . . .  40  41
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  41  42

1.  Introduction

   [RFC6707] introduces the problem scope for CDN Interconnection (CDNI)
   and lists the four categories of interfaces that may be used to
   compose a CDNI solution (Control, Metadata, Request Routing,
   Logging).

   [RFC7336] expands on the information provided in [RFC6707] and
   describes each of the interfaces and the relationships between them
   in more detail.

   This document describes the "CI/T" interface, "CDNI Control interface
   / Triggers".  It does not consider those parts of the control
   interface that relate to configuration, bootstrapping or
   authentication of CDN Interconnect interfaces.  Section 4 of
   [RFC7337] identifies the requirements specific to the CI interface,
   requirements applicable to the CI/T interface are CI-1 to CI-6.

   o  Section 2 outlines the model for the CI/T Interface at a high
      level.

   o  Section 3 describes collections of Trigger Status Resources.

   o  Section 4 defines the web service provided by the dCDN.

   o  Section 5 lists properties of CI/T Commands and Status Resources.

   o  Section 6 contains example messages.

1.1.  Terminology

   This document reuses the terminology defined in [RFC6707].

2.  Model for CDNI Triggers

   A trigger, CI/T Command, sent from the uCDN to the dCDN, is a request for the
   dCDN to do some work relating to data associated with content
   requests originating from the uCDN.

   There are two types of CI/T Command, CI/T Trigger Commands and CI/T
   Cancel Commands.  The trigger CI/T Cancel Command can be used to request action on either metadata or content,
   cancellation of an earlier CI/T Trigger Command.  A CI/T Trigger
   Command is of one of the following actions can be requested: types:

   o  preposition - used to instruct the dCDN to fetch metadata from the
      uCDN, or content from any origin including the uCDN.

   o  invalidate - used to instruct the dCDN to revalidate specific
      metadata or content before re-using it.

   o  purge - used to instruct the dCDN to delete specific metadata or
      content.

   Multiple representations of an HTTP resource may share the same URL.
   Requests to invalidate and purge metadata or content apply to all
   resource representations with matching URLs.

   The CI/T interface is a web service offered by the dCDN.  It allows
   creation and deletion of triggers,
   CI/T commands to be issued, and tracking of the triggered
   activity. activity to be tracked.
   When the dCDN accepts a trigger CI/T Command it creates a resource describing
   status of the triggered activity, a Trigger Status Resource.  The
   uCDN can poll Trigger Status Resources to monitor progress.

   The dCDN maintains a at least one collection of Trigger Status
   Resources for each
   uCDN, each uCDN.  Each uCDN only has access to its own collection and
   collections, the
   location locations of that collection is which are shared when CDN
   interconnection is established.

   To trigger activity in the dCDN, the uCDN POSTs a CI/T Command to the
   collection of Trigger Status Resources.  If the dCDN accepts the
   trigger, CI/T
   Command, it creates a new Trigger Status Resource and returns its
   location to the uCDN.  To monitor progress, the uCDN can GET the
   Trigger Status Resource.  To request cancellation of a trigger CI/T Trigger
   Command the uCDN can POST to the collection of Trigger Status
   Resources, or simply DELETE the Trigger Status Resource.

   In addition to the collection of all Trigger Status Resources for the
   uCDN, the dCDN can maintain filtered views of that collection.  These
   filtered views are defined in Section 3 and include collections of
   Trigger Status Resources corresponding to active and completed triggers. CI/T
   Trigger Commands.  These collections provide a mechanism for polling
   the status of multiple jobs.

   Figure 1 is an example showing the basic message flow used by the
   uCDN to trigger activity in the dCDN, and for the uCDN to discover
   the status of that activity.  Only successful triggering is shown.
   Examples of the messages are given in Section 6.

      uCDN                                                   dCDN
       |    (1) POST http://dcdn.example.com/triggers/uCDN     |
      [ ] --------------------------------------------------> [ ]--+
       |                                                      [ ]  | (2)
       |    (3) HTTP 201 Response                             [ ]<-+
      [ ] <-------------------------------------------------- [ ]
       |     Loc: http://dcdn.example.com/triggers/uCDN/123    |
       |                                                       |
       .                           .                           .
       .                           .                           .
       .                           .                           .
       |                                                       |
       |   (4) GET http://dcdn.example.com/triggers/uCDN/123   |
      [ ] --------------------------------------------------> [ ]
       |                                                      [ ]
       |   (5) HTTP 200 Trigger Status Resource               [ ]
      [ ] <-------------------------------------------------- [ ]
       |                                                       |
       |                                                       |

              Figure 1: Basic CDNI Message Flow for Triggers

   The steps in Figure 1 are:

   1.  The uCDN triggers action in the dCDN by posting a CI/T Command to
       a collection of Trigger Status Resources,
       "http://dcdn.example.com/triggers/uCDN".  The URL of this was
       given to the uCDN when the trigger CI/T interface was established.

   2.  The dCDN authenticates the request, validates the trigger and CI/T Command
       and, if it accepts the request, creates a new Trigger Status
       Resource.

   3.  The dCDN responds to the uCDN with an HTTP 201 response status,
       and the location of the Trigger Status Resource.

   4.  The uCDN can repeatedly poll poll, possibly repeatedly, the Trigger Status
       Resource in the dCDN.

   5.  The dCDN responds with the Trigger Status Resource, describing
       progress or results of the triggered activity. CI/T Trigger Command.

   The remainder of this document describes the messages, Trigger Status
   Resources, and collections of Trigger Status Resources in more
   detail.

2.1.  Timing of Triggered Activity

   Timing of the execution of triggered activity CI/T Commands is under the dCDN's control,
   including its start-time and pacing of the activity in the network.

   Invalidate

   CI/T invalidate and purge triggers commands MUST be applied to all data
   acquired before the trigger command was created in accepted by the dCDN.  The dCDN MAY
   SHOULD NOT apply the
   triggers CI/T invalidate and purge commands to data acquired
   after trigger creation. the CI/T Command was accepted, but this may not always be
   achievable so the uCDN cannot count on that.

   If the uCDN wishes to invalidate or purge content, content then immediately
   pre-position replacement content at the same URLs, it SHOULD ensure
   the dCDN has completed the invalidate/purge before initiating the
   prepositioning.  Otherwise, there is a risk that the dCDN pre-
   positions the new content, then immediately invalidates or purges it
   (as a result of the two uCDN requests running in parallel).

   Because the CI/T Command timing is under the dCDN's control, the dCDN
   implementation can choose whether to apply CI/T invalidate and purge
   commands to content acquisition that has already started when the
   command is received.

2.2.  Trigger Results  Scope of Triggered Activity

   Each trigger CI/T Command can operate on multiple metadata and content URLs.

   Multiple representations of an HTTP resource may share the same URL.
   CI/T Trigger Commands that invalidate or purge metadata or content
   apply to all resource representations with matching URLs.

   The
   trigger dCDN MUST reject CI/T Commands from a uCDN that act on another
   uCDN's data.  Security considerations are discussed further in
   section Section 8.

2.3.  Trigger Results

   Possible states for a Trigger Status Resource are defined in section
   Section 5.2.3.

   The CI/T Trigger Command MUST NOT be reported as "complete" 'complete' until all
   actions have been completed successfully.  The reasons for failure,
   and URLs or Patterns affected, SHOULD be enumerated in the Trigger
   Status Resource.  For more detail, see section Section 4.7.

   If a dCDN is also acting as a uCDN in a cascade, it MUST forward
   triggers CI/T
   Commands to any downstream CDNs that may have data affected by the
   trigger. be affected.  The trigger CI/T
   Trigger Command MUST NOT be reported as 'complete' in a CDN until it
   is 'complete' in all of its downstream CDNs.  If a trigger CI/T Trigger
   Command is reported as 'processed' in any dCDN, intermediate CDNs
   MUST NOT report 'complete', instead they must also report
   'processed'.  A
   trigger CI/T Command MAY be reported as 'failed' as soon as
   it fails in a CDN or in any of its downstream CDNs.  A cancelled trigger CI/T
   Trigger Command MUST be reported as 'cancelling' until it has been
   reported as 'cancelled', 'complete', or 'failed' by all dCDNs in a
   cascade.

3.  Collections of Trigger Status Resources

   As described in Section 2, Trigger Status Resources exist in the dCDN
   to report the status of activity triggered by each uCDN.

   A collection of Trigger Status Resources is a resource that contains
   a reference to each Trigger Status Resource in that collection.

   The dCDN MUST make a collection of a uCDN's Trigger Status Resources
   available to that uCDN.  This collection includes all of the Trigger
   Status Resources created for CI/T Commands from the uCDN
   triggers that have
   been accepted by the dCDN, and have not yet been deleted by the uCDN,
   or expired and removed by the dCDN (as described in section
   Section 4.4).  Trigger Status Resources belonging to a uCDN MUST NOT
   be visible to any other CDN.  The dCDN could, for example, achieve
   this by offering different collection URLs to each uCDN, or and/or by
   filtering the response based on the uCDN with which the HTTP client uCDN.
   is associated.

   To trigger activity in a dCDN, or to cancel triggered activity, the
   uCDN POSTs a CI/T Command to the dCDN's collection of the uCDN's
   Trigger Status Resources.

   In order to allow the uCDN to check the status of multiple jobs in a
   single request, the dCDN SHOULD also maintain collections
   representing filtered views of the collection of all Trigger Status
   Resources.  If it implements these  These filtered collections, collections are optional-to-implement but,
   if implemented, the dCDN MUST include links to them in the collection
   of all triggers. Trigger Status Resources.  The filtered collections are:

   o  Pending - Trigger Status Resources for triggers CI/T Trigger Commands that
      have been accepted, but not yet acted upon.

   o  Active - Trigger Status Resources for triggered activity CI/T Trigger Commands that is
      are currently being processed in the dCDN.

   o  Complete - Trigger Status Resources representing activity that
      completed successfully successfully, and 'processed' triggers CI/T Trigger Commands for
      which no further status updates will be made by the dCDN.

   o  Failed - Trigger Status Resources representing activity CI/T Commands that
      failed
      failes or was were cancelled by the uCDN.

4.  CDNI Trigger Interface

   This section describes an interface to enable an upstream CDN to
   trigger activity in a downstream CDN.

   Requests are made over HTTP, and the HTTP Method defines the
   operation the request would like to perform.

   The corresponding HTTP
   Response returns the status CI/T interface builds on top of the operation in the HTTP Status Code
   and returns the current representation HTTP, so dCDNs may make use of the resource (if
   appropriate) in the Response Body.
   any HTTP Responses from dCDNs feature when implementing the CI/T that contain interface.  For example,
   a response body dCDN SHOULD include an ETag
   to enable validation make use of cached versions HTTP's caching mechanisms to indicate that
   a requested response/representation has not been modified, reducing
   the uCDN's processing needed to determine whether the status of returned resources.
   triggered activity has changed.

   All dCDNs implementing CI/T MUST support the HTTP GET, HEAD, POST and
   DELETE methods as defined in [RFC7231].

   The only representation specified in this document is JSON,
   [RFC7159].  It MUST be supported by the uCDN and by the dCDN.

   The URL of the dCDN's collection of all Trigger Status Resources
   needs to be either discovered by, or configured in, the uCDN.  The
   mechanism for discovery of that URL is outside the scope of this
   document.

   CI/T Commands are POSTed to the dCDN's collection of all Trigger
   Status Resources.  If a command to create a new trigger CI/T Trigger Command is accepted by the dCDN, it
   the dCDN creates a new Trigger Status Resource and returns its URI to
   the dCDN uCDN in an HTTP 201 response.  The triggered activity can then be
   monitored by the uCDN using that resource and the collections
   described in Section 3.

   The URI of each Trigger Status Resource is returned to the uCDN when
   it is created. created, and URIs of all Trigger Status Resources are listed in
   the dCDN's collection of all Trigger Status Resources.  This means
   all Trigger Status Resources can be
   discovered, discovered by the uCDN, so dCDNs
   are free to assign whatever structure they desire to the URIs for CI/T CI/
   T resources.  Therefore uCDNs MUST NOT make
   any assumptions regarding the structure of CI/T URIs or the mapping
   between CI/T objects and their associated URIs.  URIs present in the
   examples in this document are purely illustrative and are not
   intended to impose a definitive structure on CI/T interface
   implementations.

   The CI/T interface builds on top of HTTP, so dCDNs may make use of
   any HTTP feature when implementing the CI/T interface.  For example,
   a dCDN SHOULD make use of HTTP's caching mechanisms to indicate that
   a requested response/representation has not been modified, reducing
   the uCDN's processing needed to determine whether the status of
   triggered activity has changed.

   The dCDN MUST ensure that activity triggered by NOT make any assumptions regarding
   the uCDN only affects
   metadata structure of CI/T URIs or content originating from that uCDN. the mapping between CI/T objects and
   their associated URIs.  URIs present in the examples in this document
   are purely illustrative and are not intended to impose a definitive
   structure on CI/T interface implementations.

4.1.  Creating Triggers

   To create issue a new trigger, CI/T Command, the uCDN makes an HTTP POST to the dCDN's
   collection of all of the uCDN's Trigger Status Resources.  The
   request body of that POST is a CI/T Command with a "trigger", Command, as described in
   Section 5.1.1.

   The dCDN validates and authenticates that request, CI/T Command, if it is
   malformed or the uCDN does not have sufficient access rights it MUST
   either respond with an appropriate 4xx HTTP error code and a resource Trigger
   Status Resource MUST NOT be created on the dCDN, or create a 'failed'
   Trigger Status Resource containing an appropriate error description.

   If the request

   When a CI/T Trigger Command is accepted, the uCDN MUST create a new
   Trigger Status
   Resource. Resource which will convey a specification of the CI/T
   Command and its current status.  The HTTP response to the dCDN MUST
   have status code 201 and MUST convey the URI of the Trigger Status
   Resource in the Location header field.  The HTTP response SHOULD
   include the content of the newly created Trigger Status Resource,
   this is recommended particularly in cases where the trigger CI/T Trigger
   Command has completed immediately.

   Once a Trigger Status Resource has been created the dCDN MUST NOT re-
   use its location, URI, even after that resource Trigger Status Resource has been
   removed.

   The "trigger" property of the Trigger Status Resource contains the
   Trigger Specification posted in the body dCDN SHOULD track and report on progress of the CI/T Command.  Note
   that this need not be a byte-for-byte copy.  For example, in the JSON
   representation the dCDN may re-serialise the information differently. Trigger
   Commands.  If the dCDN is not able to track the execution of triggered activity, do that, it MUST indicate that
   it has accepted the request but will not be providing further status
   updates.  To do this, it sets the "status" of the Trigger Status
   Resource to "processed".  In this case, CI/T processing should
   continue as for a "complete" request, so the Trigger Status Resource
   MUST be added to the dCDN's collection of Complete Triggers. Trigger Status
   Resources.  The dCDN SHOULD also provide an estimated completion time
   for the request, by using the "etime" property of the Trigger Status
   Resource.  This will allow the uCDN to schedule prepositioning after
   an earlier delete of the same URLs is expected to have finished.

   If the dCDN is able to track the execution of triggered activity, the
   trigger CI/T Commands and a CI/
   T Command is queued by the dCDN for later action, the "status"
   property of the Trigger Status Resource MUST be "pending".  Once trigger
   processing has started the "status" MUST be "active".  Finally, once
   the triggered activity CI/T Command is complete, the trigger status MUST be set to "complete" or
   "failed".

   A trigger CI/T Trigger Command may result in no activity in the dCDN if, for
   example, it is an invalidate or purge request for data the dCDN has
   not yet acquired, or a prepopulate request for data it has already
   acquired and which is still valid.  In this case, the "status" of the
   Trigger Status Resource MUST be "processed" or "complete", and the
   Trigger Status Resource MUST be added to the dCDN's collection of
   Complete
   Triggers. Trigger Status Resources.

   Once created, Trigger Status Resources can be cancelled or deleted by
   the uCDN, but not modified.  The dCDN MUST reject PUT and POST
   requests from the uCDN to Trigger Status Resources by responding with
   an appropriate HTTP status code.

4.2.  Checking Status

   The uCDN has two ways to check progress of activity CI/T Commands it has triggered
   in
   issued to the dCDN, described in sections Section 4.2.1 and
   Section 4.2.2.

   To check for change in status of a resource Trigger Status Resource or
   collection of
   resources Trigger Status Resources without re-fetching the whole resource
   Resource or collection, Collection, Entity Tags SHOULD be included by the dCDN
   for the uCDN to use as cache validators, as defined in [RFC7232].

   The dCDN SHOULD use the cache control headers for responses to GETs
   for Trigger Status Resources and Collections to indicate the
   frequency at which it recommends the uCDN should poll for change.

4.2.1.  Polling Trigger Status Resource collections

   The uCDN can fetch the collection of its Trigger Status Resources, or
   filtered views of that collection.

   This makes it possible to poll status of all triggered activity CI/T Trigger Commands in
   a single request.  If the dCDN moves a Trigger Status Resource from
   the Active to the Completed collection, the uCDN can fetch the result
   of that activity.

   When polling in this way, the uCDN SHOULD use HTTP Entity Tags to
   monitor for change, rather than repeatedly fetching the whole
   collection.

4.2.2.  Polling Trigger Status Resources

   The uCDN has a URI provided by the dCDN for each Trigger Status
   Resource it has created, it may fetch that resource Trigger Status Resource at
   any time.

   This can be used to retrieve progress information, and to fetch the
   result of triggered activity. the CI/T Command.

   When polling in this way, the uCDN SHOULD use HTTP Entity Tags to
   monitor for change, rather than repeatedly fetching the Trigger
   Status Resource.

4.3.  Cancelling Triggers

   The uCDN can request cancellation of a trigger CI/T Trigger Command by
   POSTing a Trigger
   "cancel" CI/T Cancel Command to the collection of all triggers. Trigger Status
   Resources.

   Cancellation of a CI/T Trigger Command is optional-to-implement in
   the dCDN.

   The uCDN should dCDN MUST respond to that command the CI/T Cancel Command appropriately, for
   example with HTTP status code 200 "OK" if the cancellation has been
   processed and the trigger CI/T Command is inactive, 202 "Accepted" if the
   command has been accepted but the trigger CI/T Command remains active, or 403
   "Forbidden" if cancellation is not supported by the dCDN.

   If cancellation of a "pending" Trigger Status Resource is accepted by
   the dCDN, the dCDN SHOULD NOT start processing of that activity.
   Cancelling
   Issuing a CT/T cancel command for a "pending" trigger Trigger Status Resource
   does not however guarantee that not the corresponding activity is will not
   be started, because the uCDN cannot control the timing of that
   activity.  Processing could, for example, start after the POST is
   sent by the uCDN but before that request is processed by the dCDN.

   If cancellation of an "active" or "processed" Trigger Status Resource
   is accepted by the dCDN, the dCDN SHOULD stop processing the
   triggered activity. CI/T
   Command.  However, as with cancellation of a "pending"
   trigger, CI/T Command,
   the dCDN does not guarantee this.

   If the triggered activity CI/T Command cannot be stopped immediately, the
   trigger's status in the
   corresponding Trigger Status Resource MUST be set to "cancelling" "cancelling",
   and the Trigger Status Resource remains MUST remain in the collection of
   Trigger Status Resources for active triggers. CI/T Commands.  If processing is
   stopped before normal completion, the trigger's status value in the Trigger
   Status Resource MUST be set to "cancelled" "cancelled", and the Trigger Status
   Resource MUST be included in the collection of failed triggers. CT/T Trigger
   Commands.

   Cancellation of a "complete" or "failed" Trigger Status Resource
   requires no processing in the dCDN, its status MUST NOT be changed to
   "cancelled".

4.4.  Deleting Triggers

   The uCDN can delete Trigger Status Resources at any time, using the
   HTTP DELETE method.  The effect is similar to cancellation, but no
   Trigger Status Resource remains afterwards.

   Once deleted, the references to a Trigger Status Resource MUST be
   removed from all Trigger Status Resource collections.  Subsequent
   requests to GET the deleted resource Trigger Status Resource SHOULD fail. be
   rejected by the dCDN with an HTTP error.

   If a "pending" Trigger Status Resource is deleted, the dCDN SHOULD
   NOT start processing of that activity.  Deleting a "pending" trigger Trigger
   Status Resource does not however guarantee that it has not started
   because the uCDN cannot control the timing of that activity.
   Processing may, for example, start after the DELETE is sent by the
   uCDN but before that request is processed by the dCDN.

   If an "active" or "processed" Trigger Status Resource is deleted, the
   dCDN MAY SHOULD stop processing the triggered activity. CI/T Command.  However, as with
   deletion of a "pending" trigger, Trigger Status Resource, the dCDN does not
   guarantee this.

   Deletion of a "complete" or "failed" Trigger Status Resource requires
   no processing in the dCDN other than deletion of the resource. Trigger Status
   Resource.

4.5.  Expiry of Trigger Status Resources

   The dCDN can choose to automatically delete Trigger Status Resources
   some time after they become "complete", "processed", "failed" or
   "cancelled".  In this case, the dCDN will remove the resource Trigger Status
   Resource and respond to subsequent requests for it with an HTTP
   error.

   If the dCDN performs this housekeeping, it MUST have reported the
   length of time after which completed Trigger Status Resources will be
   deleted via a property of the collection of all Trigger Status
   Resources.  It is recommended RECOMMENDED that Trigger Status Resources are not
   automatically deleted by the dCDN for at least 24 hours after they
   become "complete", "processed", "failed" or "cancelled".

   To ensure it is able to get the status of its Trigger Status
   Resources for completed and failed
   triggers, CI/T Commands, it is recommended RECOMMENDED
   that the uCDN's uCDN polling interval is less than the time after which
   records for completed activity will be deleted.

4.6.  Loop Detection and Prevention

   Given three CDNs, A, B and C.  If CDNs B and C delegate delivery of
   CDN A's content to each other, CDN A's triggers CI/T Commands could be passed
   between CDNs B and C in a loop.  More complex networks of CDNs could
   contain similar loops involving more hops.

   In order to prevent and detect such CI/T loops, each CDN uses a CDN
   Provider ID to uniquely identify itself.  Each CDN MUST insert its
   CDN Provider ID into the cdn-path key of every CI/T Command it
   originates or cascades.  When receiving CI/T commands Commands a dCDN MUST
   check the cdn-path and reject any CI/T Command which already contains
   its own CDN Provider ID in the cdn-path.  Transit CDNs MUST check the
   cdn-path and not cascade the CI/T Command to dCDNs that are already
   listed in cdn-path.

   The CDN Provider Id consists of the two characters AS "AS" followed by
   the CDN Provider's AS Autonomous System number, then a colon (':') and
   an additional qualifier that is used to guarantee uniqueness in case
   a particular AS has multiple independent CDNs deployed.  For example
   "AS64496:0".

   If the CDN provider has multiple Autonomous Systems, the same AS
   number SHOULD be used in all messages from that CDN provider, unless
   there are multiple distinct CDNs.

   If the RI interface described in [I-D.ietf-cdni-redirection] is
   implemented by the dCDN, the CI/T and RI interfaces SHOULD use the
   same CDN Provider Id.

4.7.  Error Handling

   A dCDN can reject signal rejection of a CI/T Command using HTTP status
   codes.  For example, 400 if the request is malformed, or 401 if the
   uCDN does not have permission to create triggers issue CI/T Commands or it is trying
   to act on another CDN's data.

   If any part of the trigger CI/T Trigger Command fails, the trigger SHOULD be
   reported as "failed" once its activity is complete or if no further
   errors will be reported.  The "errors" property in the Trigger Status
   Resource will be used to enumerate which actions failed and the
   reasons for failure, and can be present while the trigger Trigger Status
   Resource is still "pending" or "active", if the trigger CI/T Trigger Command
   is still running for some URLs or Patterns in the Trigger
   Specification.

   Once a request has been accepted, processing errors are reported in
   the Trigger Status Resource using a list of Error Descriptions.  Each
   Error Description is used to report errors against one or more of the
   URLs or Patterns in the Trigger Specification.

   If a surrogate affected by a trigger CI/T Trigger Command is offline in the
   dCDN, or the dCDN is unable to pass a CI/T Command on to any of its
   cascaded dCDNs:

   o  If the request CI/T Command is abandoned by the dCDN, the dCDN SHOULD
      report an error.

   o  An  A CI/T "invalidate" trigger command may be reported as "complete" when
      surrogates that may have the data are offline.  In this case,
      surrogates MUST NOT use the affected data without first
      revalidating it when they are back online.

   o  CI/T "preposition" and "purge" triggers commands can be reported as
      "processed" if affected caches are offline and the activity will
      complete when they return to service.

   o  Otherwise, the dCDN SHOULD keep the trigger Trigger Status Resource in
      state "pending" or "active" until the trigger CI/T Command is acted upon,
      or the uCDN chooses to cancel it.

4.8.  Content URLs

   To refer to content in the dCDN, the uCDN MUST present URLs in the
   same form as in the metadata it supplied to the dCDN.  By definition,
   it is always possible for the dCDN to locate content based on URLs in
   this form.

   Therefore, if content URLs are transformed by an intermediate CDN in
   a cascade, that intermediate CDN MUST transform URLs in CI/T commands Commands
   it passes to its dCDN.

   When processing Trigger Specifications, CDNs MUST ignore the URL
   scheme (http or https) in comparing URLs.  For example, for an a CI/T
   invalidate or purge trigger, command, content MUST be invalidated or purged
   regardless of the protocol clients use to request it.

5.  CI/T Object Properties and Encoding

   CI/T Commands, Trigger Status Resources and Trigger Collections and
   their properties are encoded using JSON, as defined in sections
   Section 5.1.1, Section 5.2.1, and Section 5.1.2.

   Names in JSON are case sensitive and therefore the sensitive.  The names and literal values
   specified here in the present document MUST always use lower-case.

   Unrecognised name/value pairs in JSON objects SHOULD NOT be treated
   as an error by either the uCDN or dCDN.  They SHOULD be ignored in
   the processing, and passed on by dCDN to any further dCDNs in a
   cascade.

5.1.  CI/T Objects

   The top-level objects defined by the CI/T interface are described in
   this section.  Each has an associated MIME Media Type.  The encoding
   of values used by these objects is described in Section 5.2.

5.1.1.  CI/T Commands

   CI/T Commands SHOULD use a MIME Media Type of application/
   cdni.ci.TriggerCommand+json.

   A CI/T Command is encoded as a JSON object containing the following
   name/value pairs.

      Name: trigger

         Description: A specification of the trigger type, and a set of
         data to act upon.

         Value: A Trigger Specification, as defined in Section 5.2.1.

         Mandatory: No, but exactly one of "trigger" or "cancel" MUST be
         present in a CI/T Command.

      Name: cancel

         Description: The URLs of Trigger Status Resources for triggers CI/T
         Trigger Commands that the uCDN wants to cancel.

         Value: A JSON array of URLs represented as JSON strings.

         Mandatory: No, but exactly one of "trigger" or "cancel" MUST be
         present in a CI/T Command.

      Name: cdn-path

         Description: The CDN Provider Identifiers of CDNs that have
         already accepted the CI/T Command.

         Value: A JSON array of JSON strings, where each string is a CDN
         Provider Identifier as defined in Section 4.6.

         Mandatory: Yes.

5.1.2.  Trigger Status Resource

   Trigger Status Resources SHOULD use a MIME Media Type of application/
   cdni.ci.TriggerStatus+json.

   A Trigger Status Resource is encoded as a JSON object containing the
   following name/value pairs.

      Name: trigger

         Description: The Trigger Specification posted in the body of
         the CI/T Command.  Note that was used to create this Trigger Status Resource. need not be a byte-for-byte
         copy.  For example, in the JSON representation the dCDN may re-
         serialise the information differently.

         Value: A Trigger Specification, as defined in Section 5.2.1.

         Mandatory: Yes

      Name: ctime

         Description: Time at which the CI/T Command was received by the
         dCDN.  Time is determined by the dCDN, there is no requirement
         to synchronise clocks between interconnected CDNs.

         Value: Absolute Time, as defined in Section 5.2.5.

         Mandatory: Yes

      Name: mtime

         Description: Time at which the Trigger Status Resource was last
         modified.  Time is determined by the dCDN, there is no
         requirement to synchronise clocks between interconnected CDNs.

         Value: Absolute Time, as defined in Section 5.2.5.

         Mandatory: Yes

      Name: etime

         Description: Estimate of the time at which the dCDN expects to
         complete the activity.  Time is determined by the dCDN, there
         is no requirement to synchronise clocks between interconnected
         CDNs.

         Value: Absolute Time, as defined in Section 5.2.5.

         Mandatory: No

      Name: status

         Description: Current status of the triggered activity.

         Value: Trigger Status, as defined in Section 5.2.3.

         Mandatory: Yes

      Name: errors

         Description: Descriptions of errors that have occurred while
         processing a Trigger Command.

         Value: A list of Error Descriptions, as defined in
         Section 5.2.6.

         Mandatory: No.

5.1.3.  Trigger Collection

   Trigger Collections SHOULD use a MIME Media Type of application/
   cdni.ci.TriggerCollection+json.

   A Trigger Collection is encoded as a JSON object containing the
   following name/value pairs.

      Name: triggers

         Description: Links to Trigger Status Resources in the
         collection.

         Value: A JSON array of URLs represented as JSON strings.

         Mandatory: Yes

      Name: staleresourcetime
         Description: The length of time for which the dCDN guarantees
         to keep a completed Trigger Status Resource.  After this time,
         the dCDN SHOULD delete the resource Trigger Status Resource and all
         references to it from collections.

         Value: A JSON number, integer time in seconds.

         Mandatory: Yes, in the collection of all Trigger Status
         Resources if the dCDN deletes stale entries.  If the property
         is present in the filtered collections, it MUST have the same
         value as in the collection of all Trigger Status Resources.

      Names: coll-all, coll-pending, coll-active, coll-complete, coll-
      failed

         Description: Link to a Trigger Collection.

         Value: A URL represented as a JSON string.

         Mandatory: Links to all of the filtered collections are
         mandatory in the collection of all Trigger Status Resources, if
         the dCDN implements the filtered collections.  Otherwise,
         optional.

      Name: cdn-id

         Description: The CDN Provider Identifier of the dCDN.

         Value: A JSON string, the dCDN's CDN Provider Identifier, as
         defined in Section 4.6.

         Mandatory: Only in the collection of all Trigger Status
         Resources, if the dCDN implements the filtered collections.
         Optional filtered collections.
         Optional in the filtered collections (the uCDN can always find
         the dCDN's cdn-id in the collection of all Trigger Status
         Resources, but the dCDN can choose to repeat that information
         in the its implementation of filtered collections. collections).

5.2.  Properties of CI/T Objects

   This section defines the values that can appear in the top level
   objects described in Section 5.1, and their encodings.

5.2.1.  Trigger Specification

   A Trigger Collection is encoded as a JSON object containing the
   following name/value pairs.

   An unrecognised name/value pair in the Trigger Specification object
   contained in a CI/T Command SHOULD be preserved in the Trigger
   Specification of any Trigger Status Resource it creates.

      Name: type

         Description: This property defines the type of the trigger. CI/T Trigger
         Command.

         Value: Trigger Type, as defined in Section 5.2.2.

         Mandatory: Yes

      Name: metadata.urls

         Description: The uCDN URLs of the metadata the trigger CI/T Trigger
         Command applies to.

         Value: A JSON array of URLs represented as JSON strings.

         Mandatory: No, but at least one of 'metadata.*' or 'content.*'
         MUST be present and non-empty.

      Name: content.urls

         Description: URLs of content the trigger CI/T Trigger Command applies
         to, see Section 4.8.

         Value: A JSON array of URLs represented as JSON strings.

         Mandatory: No, but at least one of 'metadata.*' or 'content.*'
         MUST be present and non-empty.

      Name: content.ccid

         Description: The Content Collection Identifier of content the
         trigger applies to.  The 'ccid' is a grouping of content, as
         defined by [I-D.ietf-cdni-metadata].

         Value: A JSON array of strings, where each string is a Content
         Collection Identifier.

         Mandatory: No, but at least one of 'metadata.*' or 'content.*'
         MUST be present and non-empty.

      Name: metadata.patterns

         Description: The metadata the trigger applies to.

         Value: A JSON array of Pattern Match, as defined in
         Section 5.2.4.

         Mandatory: No, but at least one of 'metadata.*' or 'content.*'
         MUST be present and non-empty, and metadata.patterns MUST NOT
         be present if the TriggerType is Preposition.

      Name: content.patterns

         Description: The content data the trigger applies to.

         Value: A JSON array of Pattern Match, as defined in
         Section 5.2.4.

         Mandatory: No, but at least one of 'metadata.*' or 'content.*'
         MUST be present and non-empty, and content.patterns MUST NOT be
         present if the TriggerType is Preposition.

5.2.2.  Trigger Type

   Trigger Type is used in a Trigger Specification to describe trigger
   action.  It MUST be one of the JSON strings in the following table:

   +-------------+-----------------------------------------------------+
   | JSON String | Description                                         |
   +-------------+-----------------------------------------------------+
   | preposition | A request for the dCDN to acquire metadata or       |
   |             | content.                                            |
   | invalidate  | A request for the dCDN to invalidate metadata or    |
   |             | content. After servicing this request the dCDN will |
   |             | not use the specified data without first re-        |
   |             | validating it using, for example, an "If-None-      |
   |             | Match" HTTP request. The dCDN need not erase the    |
   |             | associated data.                                    |
   | purge       | A request for the dCDN to erase metadata or         |
   |             | content. After servicing the request, the specified |
   |             | data MUST NOT be held on the dCDN. dCDN (the dCDN should  |
   |             | re-acquire the metadata or content from uCDN if it  |
   |             | needs it).                                          |
   +-------------+-----------------------------------------------------+

5.2.3.  Trigger Status

   This describes the current status of a Trigger.  It MUST be one of
   the JSON strings in the following table:

   +------------+------------------------------------------------------+
   | JSON       | Description                                          |
   | String     |                                                      |
   +------------+------------------------------------------------------+
   | pending    | The trigger CI/T Trigger Command has not yet been acted      |
   |            | upon.                                                |
   | active     | The trigger CI/T Trigger Command is currently being acted    |
   |            | upon.                                                |
   | complete   | The triggered activity CI/T Trigger Command completed successfully.     |
   | processed  | The trigger CI/T Trigger Command has been accepted and no further status    |
   |            | further status update will be made (can be used in cases where   |
   |            | cases where completion cannot be confirmed).         |
   | failed     | The triggered activity CI/T Trigger Command could not be completed.     |
   | cancelling | The triggered activity Processing of the CI/T Trigger Command is still in   |
   |            | progress, but the CI/T Trigger Command has been      |
   |            | trigger has been cancelled by the uCDN.                               |
   | cancelled  | The triggered activity CI/T Trigger Command was cancelled by the uCDN.  |
   +------------+------------------------------------------------------+

5.2.4.  PatternMatch

   A Pattern Match consists of a string pattern to match, and flags
   describing the type of match.

   It is encoded as a JSON object with the following name/value pairs:

      Name: pattern

         Description: A pattern for string matching.

         Value: A JSON string representing the pattern.  The pattern may
         contain the wildcards * and ?, where * matches any sequence of
         characters (including the empty string) and ? matches exactly
         one character.  The three literals "\" , "*" and "?"  MUST be
         escaped as "\\", "\*" and "\?".

         Mandatory: Yes.

      Name: case-sensitive

         Description: Flag indicating whether or not case-sensitive
         matching should be used.

         Value: One of the JSON values 'true' or 'false'.

         Mandatory: No, default is case-insensitive match.

      Name: match-query-string
         Description: Flag indicating whether or not the query string
         should be included in the pattern match.

         Value: One of the JSON values 'true' or 'false'.

         Mandatory: No, default is not to include the query string in
         the pattern match.

   Example of case-sensitive prefix match against
   "http://www.example.com/trailers/":

   {
       "pattern": "http://www.example.com/trailers/*",
       "case-sensitive": true
   }

5.2.5.  Absolute Time

   A JSON number, seconds since the UNIX epoch.

5.2.6.  Error Description

   An Error Description is used to report failure of a Trigger CI/T Command, or
   in the activity it triggered.

      Name: error

         Value: Error Code, as defined in Section 5.2.7.

         Mandatory: Yes.

      Names: metadata.urls, content.urls, metadata.patterns,
      content.patterns

         Description: Metadata and content references copied from the
         Trigger Specification.  Only those URLs and patterns to which
         the error applies are included in each property, but those URLs
         and patterns MUST be exactly as they appear in the request, the
         dCDN MUST NOT generalise the URLs.  (For example, if the uCDN
         requests prepositioning of URLs "http://content.example.com/a"
         and "http://content.example.com/b", the dCDN must not
         generalise its error report to Pattern
         "http://content.example.com/*".)

         Value: A JSON array of JSON strings, where each string is
         copied from a 'content.*' or 'metadata.*' value in the
         corresponding Trigger Specification.

         Mandatory: At least one of these name/value pairs is mandatory
         in each Error Description object.

      Name: description

         Description: A human-readable description of the error.

         Value: A JSON string, the human-readable description.

         Mandatory: No.

5.2.7.  Error Code

   This type is used by the dCDN to report failures in trigger
   processing.

   +------------+------------------------------------------------------+
   | Error Code | Description                                          |
   +------------+------------------------------------------------------+
   | emeta      | The dCDN was unable to acquire metadata required to  |
   |            | fulfil the request.                                  |
   | econtent   | The dCDN was unable to acquire content (preposition (CT/T         |
   |            | triggers preposition commands only).                          |
   | eperm      | The uCDN does not have permission to trigger issue the CI/T  |
   |            | requested activity Command (for example, the data is owned by another   |
   |            | by another CDN).                                                |
   | ereject    | The dCDN is not willing to fulfil the request (for CI/T Command   |
   |            | (for example, a preposition request for content at a time |
   |            | time when the dCDN would not accept Request Routing  |
   |            | requests from the uCDN).                             |
   | ecdn       | An internal error in the dCDN or one of its          |
   |            | downstream CDNs.                                     |
   | ecancelled | The uCDN cancelled the request.                      |
   +------------+------------------------------------------------------+

6.  Examples

   The following sections provide examples of different CI/T objects
   encoded as JSON.

   Discovery of the triggers interface is out of scope of this document.
   In an implementation, all CI/T URLs are under the control of the
   dCDN.  The uCDN MUST NOT attempt to ascribe any meaning to individual
   elements of the path.

   In examples in this section, the URL 'http://dcdn.example.com/
   triggers' is used as the location of the collection of all triggers, Trigger
   Status Resources, and the CDN Provider Id of uCDN is "AS64496:1".

6.1.  Creating Triggers

   Examples of the uCDN triggering activity in the dCDN:

6.1.1.  Preposition

   An example of a CI/T preposition request, command, a POST to the "AllTriggers"
   collection. collection of
   all Trigger Status Resources.

   Note that "metadata.patterns" and "content.patterns" are not allowed
   in a preposition Trigger Specification.

   REQUEST:

     POST /triggers HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*
     Content-Type: application/cdni.ci.TriggerCommand+json
     Content-Length: 347

     {
       "trigger" : {
         "type": "preposition",

         "metadata.urls" : [ "http://metadata.example.com/a/b/c" ],
         "content.urls" : [
             "http://www.example.com/a/b/c/1",
             "http://www.example.com/a/b/c/2",
             "http://www.example.com/a/b/c/3",
             "http://www.example.com/a/b/c/4"
           ]
       },
       "cdn-path" : [ "AS64496:1" ]
     }

   RESPONSE:

     HTTP/1.1 201 Created
     Date: Sun, 31 Aug 2014 09:53:18 GMT
     Content-Length: 472
     Content-Type: application/cdni.ci.TriggerStatus+json
     Location: http://dcdn.example.com/triggers/0
     Server: example-server/0.1

     {
         "ctime": 1409478798,
         "etime": 1409478806,
         "mtime": 1409478798,
         "status": "pending",
         "trigger": {
             "content.urls": [
                 "http://www.example.com/a/b/c/1",
                 "http://www.example.com/a/b/c/2",
                 "http://www.example.com/a/b/c/3",
                 "http://www.example.com/a/b/c/4"
             ],
             "metadata.urls": [
                 "http://metadata.example.com/a/b/c"
             ],
             "type": "preposition"
         }
     }

6.1.2.  Invalidate

   An example of an a CI/T invalidate request, command, another POST to the
   "AllTriggers" collection.
   collection of all Trigger Status Resources.  This instructs the dCDN
   to re-validate the content at "http://www.example.com/a/index.html",
   as well as any metadata and content whose URLs are prefixed by
   "http://metadata.example.com/a/b/" using case-insensitive matching,
   and "http://www.example.com/a/b/" respectively, using case-insensitive case-sensitive
   matching.

   REQUEST:

     POST /triggers HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*
     Content-Type: application/cdni.ci.TriggerCommand+json
     Content-Length: 384

     {
       "trigger" : {
         "type": "invalidate",

         "metadata.patterns" : [
             { "pattern" : "http://metadata.example.com/a/b/*" }
           ],

         "content.urls" : [ "http://www.example.com/a/index.html" ],
         "content.patterns" : [
             { "pattern" : "http://www.example.com/a/b/*",
               "case-sensitive" : true
             }

           ]
       },
       "cdn-path" : [ "AS64496:1" ]
     }

   RESPONSE:

     HTTP/1.1 201 Created
     Date: Sun, 31 Aug 2014 09:53:19 GMT
     Content-Length: 551
     Content-Type: application/cdni.ci.TriggerStatus+json
     Location: http://dcdn.example.com/triggers/1
     Server: example-server/0.1

     {
         "ctime": 1409478799,
         "etime": 1409478807,
         "mtime": 1409478799,
         "status": "pending",
         "trigger": {
             "content.patterns": [
                 {
                     "case-sensitive": true,
                     "pattern": "http://www.example.com/a/b/*"
                 }
             ],
             "content.urls": [
                 "http://www.example.com/a/index.html"
             ],
             "metadata.patterns": [
                 {
                     "pattern": "http://metadata.example.com/a/b/*"
                 }
             ],
             "type": "invalidate"
         }
     }

6.2.  Examining Trigger Status

   Once triggers Trigger Status Resources have been created, the uCDN can check
   their status as shown in these examples.

6.2.1.  Collection of All Triggers

   The uCDN can fetch the set collection of all the triggers Trigger Status Resources it
   has created and
   which that have not yet been deleted or removed as expired.

   After creation of the "preposition" and "invalidate" triggers shown
   above, this collection might look as follows:

   REQUEST:

     GET /triggers HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*

   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 347
     Expires: Sun, 31 Aug 2014 09:54:19 GMT
     Server: example-server/0.1
     Etag: "-6516741166528256414"
     Cache-Control: max-age=60
     Date: Sun, 31 Aug 2014 09:53:19 GMT
     Content-Type: application/cdni.ci.TriggerCollection+json

     {
         "cdn-id": "AS64496:0",
         "coll-active": "/triggers/active",
         "coll-complete": "/triggers/complete",
         "coll-failed": "/triggers/failed",
         "coll-pending": "/triggers/pending",
         "staleresourcetime": 86400,
         "triggers": [
             "http://dcdn.example.com/triggers/0",
             "http://dcdn.example.com/triggers/1"
         ]
     }

6.2.2.  Filtered Collections of Triggers Trigger Status Resources

   The filtered collections are also available to the uCDN.  Before the
   dCDN starts processing the two triggers CI/T Trigger Commands shown above,
   both will appear in the collection of Pending Triggers, for example:

   REQUEST:

     GET /triggers/pending HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*

   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 153
     Expires: Sun, 31 Aug 2014 09:54:19 GMT
     Server: example-server/0.1
     Etag: "5012053611544832286"
     Cache-Control: max-age=60
     Date: Sun, 31 Aug 2014 09:53:19 GMT
     Content-Type: application/cdni.ci.TriggerCollection+json

     {
         "staleresourcetime": 86400,
         "triggers": [
             "http://dcdn.example.com/triggers/0",
             "http://dcdn.example.com/triggers/1"
         ]
     }

   At this point, if no other triggers Trigger Status Resources had been created,
   the other filtered views of the triggers would be empty.  For example:

   REQUEST:

     GET /triggers/complete HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*

   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 56
     Expires: Sun, 31 Aug 2014 09:54:19 GMT
     Server: example-server/0.1
     Etag: "2986340333785000363"
     Cache-Control: max-age=60
     Date: Sun, 31 Aug 2014 09:53:19 GMT
     Content-Type: application/cdni.ci.TriggerCollection+json

     {
         "staleresourcetime": 86400,
         "triggers": []
     }

6.2.3.  Individual Trigger Status Resources

   The Trigger Status Resources can also be examined for detail about
   individual triggers. CI/T Trigger Commands.  For example, for the CI/T
   "preposition" and "invalidate" triggers commands from previous examples:

   REQUEST:

     GET /triggers/0 HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*

   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 472
     Expires: Sun, 31 Aug 2014 09:54:19 GMT
     Server: example-server/0.1
     Etag: "-4765587034697674779"
     Cache-Control: max-age=60
     Date: Sun, 31 Aug 2014 09:53:19 GMT
     Content-Type: application/cdni.ci.TriggerStatus+json

     {
         "ctime": 1409478798,
         "etime": 1409478806,
         "mtime": 1409478798,
         "status": "pending",
         "trigger": {
             "content.urls": [
                 "http://www.example.com/a/b/c/1",
                 "http://www.example.com/a/b/c/2",
                 "http://www.example.com/a/b/c/3",
                 "http://www.example.com/a/b/c/4"
             ],
             "metadata.urls": [
                 "http://metadata.example.com/a/b/c"
             ],
             "type": "preposition"
         }
     }

   REQUEST:

     GET /triggers/1 HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*

   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 551
     Expires: Sun, 31 Aug 2014 09:54:19 GMT
     Server: example-server/0.1
     Etag: "-7657333837290433420"
     Cache-Control: max-age=60
     Date: Sun, 31 Aug 2014 09:53:19 GMT
     Content-Type: application/cdni.ci.TriggerStatus+json

     {
         "ctime": 1409478799,
         "etime": 1409478807,
         "mtime": 1409478799,
         "status": "pending",
         "trigger": {
             "content.patterns": [
                 {
                     "case-sensitive": true,
                     "pattern": "http://www.example.com/a/b/*"
                 }
             ],
             "content.urls": [
                 "http://www.example.com/a/index.html"
             ],
             "metadata.patterns": [
                 {
                     "pattern": "http://metadata.example.com/a/b/*"
                 }
             ],
             "type": "invalidate"
         }
     }

6.2.4.  Polling for Change

   The uCDN SHOULD use the Entity Tags of collections or resources Trigger Status
   Resources when polling for change in status, as shown in the
   following examples:

   REQUEST:

     GET /triggers/pending HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*
     If-None-Match: "5012053611544832286"

   RESPONSE:

     HTTP/1.1 304 Not Modified
     Content-Length: 0
     Expires: Sun, 31 Aug 2014 09:54:19 GMT
     Server: example-server/0.1
     Etag: "5012053611544832286"
     Cache-Control: max-age=60
     Date: Sun, 31 Aug 2014 09:53:19 GMT
     Content-Type: application/cdni.ci.TriggerCollection+json

   REQUEST:

     GET /triggers/0 HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*
     If-None-Match: "-4765587034697674779"

   RESPONSE:

     HTTP/1.1 304 Not Modified
     Content-Length: 0
     Expires: Sun, 31 Aug 2014 09:54:19 GMT
     Server: example-server/0.1
     Etag: "-4765587034697674779"
     Cache-Control: max-age=60
     Date: Sun, 31 Aug 2014 09:53:19 GMT
     Content-Type: application/cdni.ci.TriggerStatus+json

   When the triggered activity CI/T Trigger Command is complete, the contents of the
   filtered collections will be updated, updated along with their Entity Tags.
   For example, when the two example triggers CI/T Trigger Commands are complete,
   the collections of pending and complete triggers Trigger Status Resources
   might look like:

   REQUEST:

     GET /triggers/pending HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*

   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 56
     Expires: Sun, 31 Aug 2014 09:54:29 GMT
     Server: example-server/0.1
     Etag: "-4471185573414616962"
     Cache-Control: max-age=60
     Date: Sun, 31 Aug 2014 09:53:29 GMT
     Content-Type: application/cdni.ci.TriggerCollection+json

     {
         "staleresourcetime": 86400,
         "triggers": []
     }

   REQUEST:

     GET /triggers/complete HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*

   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 153
     Expires: Sun, 31 Aug 2014 09:54:30 GMT
     Server: example-server/0.1
     Etag: "-1508172875796647067"
     Cache-Control: max-age=60
     Date: Sun, 31 Aug 2014 09:53:30 GMT
     Content-Type: application/cdni.ci.TriggerCollection+json

     {
         "staleresourcetime": 86400,
         "triggers": [
             "http://dcdn.example.com/triggers/0",
             "http://dcdn.example.com/triggers/1"
         ]
     }

6.2.5.  Removing a  Deleting Trigger

   To request the Status Resources

   The dCDN to cancel a Trigger, the uCDN can delete the
   Trigger Resource.  It can also delete completed and failed triggers Trigger Status Resources to
   reduce the size of the collections.  For example, to remove delete the
   "preposition" request from earlier examples:

   REQUEST:

     DELETE /triggers/0 HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*

   RESPONSE:

     HTTP/1.1 204 No Content
     Date: Sun, 31 Aug 2014 09:53:30 GMT
     Content-Length: 0
     Content-Type: text/html; charset=UTF-8
     Server: example-server/0.1

   This would, for example, cause the collection of completed triggers Trigger
   Status Resources shown in the example above to be updated to:

   REQUEST:

     GET /triggers/complete HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*

   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 106
     Expires: Sun, 31 Aug 2014 09:54:30 GMT
     Server: example-server/0.1
     Etag: "-1842390246836476263"
     Cache-Control: max-age=60
     Date: Sun, 31 Aug 2014 09:53:30 GMT
     Content-Type: application/cdni.ci.TriggerCollection+json

     {
         "staleresourcetime": 86400,
         "triggers": [
             "http://dcdn.example.com/triggers/1"
         ]
     }

6.2.6.  Error Reporting

   In this example the uCDN has requested prepositioning of
   "http://newsite.example.com/index.html", but the dCDN was unable to
   locate metadata for that site:

   REQUEST:

     GET /triggers/2 HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*

   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 505
     Expires: Sun, 31 Aug 2014 09:54:38 GMT
     Server: example-server/0.1
     Etag: "-3893590191073700822"
     Cache-Control: max-age=60
     Date: Sun, 31 Aug 2014 09:53:38 GMT
     Content-Type: application/cdni.ci.TriggerStatus+json

     {
         "ctime": 1409478810,
         "errors": [
             {
                 "content.urls": [
                     "http://newsite.example.com/index.html"
                 ],
                 "description":
                   "No HostIndex entry found for newsite.example.com",
                 "error": "emeta"
             }
         ],
         "etime": 1409478818,
         "mtime": 1409478814,
         "status": "active",
         "trigger": {
             "content.urls": [
                 "http://newsite.example.com/index.html"
             ],
             "type": "preposition"
         }
     }

7.  IANA Considerations
7.1.  Media type registrations

7.1.1.  CI/T Commands

   The MIME media type for CI/T Commands is application/
   cdni.ci.TriggerCommand+json.

   Type Name: application

   Subtype name: cdni.ci.TriggerCommand+json

   Required parameters: N/A

   Optional parameters: N/A

   Encoding considerations: binary

   Security Considerations: See [RFCthis], Section 8

   Interoperability Considerations: Described in [RFCthis]

   Published Specification: [RFCthis]

   Applications that use this media type: No known applications
   currently use this media type.

   Additional Information:

      Deprecated alias names for this type: N/A

      Magic number(s): N/A

      File Extensions: N/A

      Macintosh file type code(s): TEXT

   Person & email address to contact for further information: IESG
   <iesg@ietf.org>

   Intended Usage: COMMON

   Restrictions on usage: None

   Author: Rob Murray <rob.murray@alcatel-lucent.com>

   Change controller: IESG <iesg@ietf.org>
   Note: No "charset" parameter is defined for this registration because
   a charset parameter is not defined for application/json [RFC7159].

7.1.2.  CI/T Trigger Status Resource

   The MIME media type for CI/T Trigger Status Resources is application/
   cdni.ci.TriggerStatus+json.

   Type Name: application

   Subtype name: cdni.ci.TriggerStatus+json

   Required parameters: N/A

   Optional parameters: N/A

   Encoding considerations: binary

   Security Considerations: See [RFCthis], Section 8

   Interoperability Considerations: Described in [RFCthis]

   Published Specification: [RFCthis]

   Applications that use this media type: No known applications
   currently use this media type.

   Additional Information:

      Deprecated alias names for this type: N/A

      Magic number(s): N/A

      File Extensions: N/A

      Macintosh file type code(s): TEXT

   Person & email address to contact for further information: IESG
   <iesg@ietf.org>

   Intended Usage: COMMON

   Restrictions on usage: None

   Author: Rob Murray <rob.murray@alcatel-lucent.com>

   Change controller: IESG <iesg@ietf.org>
   Note: No "charset" parameter is defined for this registration because
   a charset parameter is not defined for application/json [RFC7159].

7.1.3.  CI/T Trigger Collection

   The MIME media type for CI/T Trigger Collections is application/
   cdni.ci.TriggerCollection+json.

   Type Name: application

   Subtype name: cdni.ci.TriggerCollection+json

   Required parameters: N/A

   Optional parameters: N/A

   Encoding considerations: binary

   Security Considerations: See [RFCthis], Section 8

   Interoperability Considerations: Described in [RFCthis]

   Published Specification: [RFCthis]

   Applications that use this media type: No known applications
   currently use this media type.

   Additional Information:

      Deprecated alias names for this type: N/A

      Magic number(s): N/A

      File Extensions: N/A

      Macintosh file type code(s): TEXT

   Person & email address to contact for further information: IESG
   <iesg@ietf.org>

   Intended Usage: COMMON

   Restrictions on usage: None

   Author: Rob Murray <rob.murray@alcatel-lucent.com>

   Change controller: IESG <iesg@ietf.org>
   Note: No "charset" parameter is defined for this registration because
   a charset parameter is not defined for application/json [RFC7159].

8.  Security Considerations

8.1.  Authentication, Confidentiality, Integrity Protection

   A CI/T dCDN server implementation MUST support TLS transport for HTTP (https) as
   per [RFC2818].  The use of TLS for transport of the CI/T interface
   allows the dCDN and the uCDN to authenticate each other (to ensure
   they are receiving CI/T Commands from, or reporting status to, an
   authenticated CDN).

   In an environment where any such protection is required, TLS SHOULD
   be used for transport of the CI/T requests and responses, unless
   alternate methods are used for ensuring that only authorised clients
   are able to access their own data (such as setting up an IPsec tunnel
   between the two CDNs, or using a physically secured internal network
   between two CDNs that are owned by the same corporate entity).  Both
   parties of the transaction (the uCDN and the dCDN) SHOULD use mutual
   authentication.

   A TLS implementation of CI/T MUST support the
   TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 cipher suite ([RFC5288]).  An
   implementation of the CI/T Interface SHOULD prefer cipher suites
   which support perfect forward secrecy over cipher suites that don't.

   HTTP requests that attempt to access or operate on CI/T data
   belonging to another CDN MUST be rejected using, for example, HTTP
   "403 Forbidden" or "404 Not Found".  This is intended to prevent
   unauthorised users from generating unnecessary load in dCDN or uCDN
   due to revalidation, reacquisition, or unnecessary acquisition.

   Note that in a "diamond" configuration, where one uCDN's content can
   be acquired via more than one directly-connected uCDN, it may not be
   possible for the dCDN to determine from which uCDN it acquired
   content.  In this case, the dCDN MUST allow each uCDN from which the
   content could have been acquired to act upon that content using CI/T
   Commands.

8.2.  Denial of Service

   This document does not define a specific mechanism to protect against
   Denial of Service (DoS) attacks on the CI/T.  However, CI/T endpoints
   can be protected against DoS attacks through the use of TLS transport
   and/or via mechanisms outside the scope of the CI/T interface, such
   as firewalling or use of Virtual Private Networks (VPNs).

   Depending on the implementation, triggered activity may consume
   significant processing and bandwidth in the dCDN.  A malicious or
   faulty uCDN could use this to generate unnecessary load in the dCDN.
   The dCDN should consider mechanisms to avoid overload, for example by
   rate-limiting acceptance or processing of CI/T Commands, or batching
   up its processing.

9.  Acknowledgements

   The authors thank Kevin Ma for his input.

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC7159]  Bray, T., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, March 2014.

   [RFC7231]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Semantics and Content", RFC 7231, June 2014.

   [RFC7232]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Conditional Requests", RFC 7232, June 2014.

10.2.  Informative References

   [I-D.ietf-cdni-metadata]
              Niven-Jenkins, B., Murray, R., Caulfield, M., Leung, K., and K. Ma,
              "CDN Interconnection Metadata", draft-ietf-
              cdni-metadata-07 draft-ietf-cdni-
              metadata-08 (work in progress), July October 2014.

   [I-D.ietf-cdni-redirection]
              Niven-Jenkins, B. and R. Brandenburg, "Request Routing
              Redirection Interface for CDN Interconnection", draft-
              ietf-cdni-redirection-03
              ietf-cdni-redirection-06 (work in progress), August December
              2014.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC5288]  Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
              Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
              August 2008.

   [RFC6707]  Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
              Distribution Network Interconnection (CDNI) Problem
              Statement", RFC 6707, September 2012.

   [RFC7336]  Peterson, L., Davie, B., and R. van Brandenburg,
              "Framework for Content Distribution Network
              Interconnection (CDNI)", RFC 7336, August 2014.

   [RFC7337]  Leung, K. and Y. Lee, "Content Distribution Network
              Interconnection (CDNI) Requirements", RFC 7337, August
              2014.

Authors' Addresses

   Rob Murray
   Velocix (Alcatel-Lucent)
   3 Ely Road
   Milton, Cambridge  CB24 6DD
   UK

   Email: rmurray@velocix.com rob.murray@alcatel-lucent.com

   Ben Niven-Jenkins
   Velocix (Alcatel-Lucent)
   3 Ely Road
   Milton, Cambridge  CB24 6DD
   UK

   Email: ben@velocix.com ben.niven-jenkins@alcatel-lucent.com