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RFC 8007

Content Delivery Network Interconnection (CDNI) Control Interface / Triggers

Pages: 49
Proposed Standard
Errata
Part 1 of 2 – Pages 1 to 27
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Top   ToC   RFC8007 - Page 1
Internet Engineering Task Force (IETF)                         R. Murray
Request for Comments: 8007                              B. Niven-Jenkins
Category: Standards Track                                          Nokia
ISSN: 2070-1721                                            December 2016


            Content Delivery Network Interconnection (CDNI)
                      Control Interface / Triggers

Abstract

This document describes the part of the Content Delivery Network Interconnection (CDNI) 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-position metadata or content or to request that it invalidate or purge metadata or content. The upstream CDN can monitor the status of activity that it has triggered in the downstream CDN. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc8007. Copyright Notice Copyright (c) 2016 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 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.
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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 ................................7 2.2.1. Multiple Interconnected CDNs ........................7 2.3. Trigger Results ............................................8 3. Collections of Trigger Status Resources .........................9 4. CDNI Trigger Interface .........................................10 4.1. Creating Triggers .........................................11 4.2. Checking Status ...........................................12 4.2.1. Polling Trigger Status Resource Collections ........12 4.2.2. Polling Trigger Status Resources ...................13 4.3. Canceling Triggers ........................................13 4.4. Deleting Triggers .........................................14 4.5. Expiry of Trigger Status Resources ........................14 4.6. Loop Detection and Prevention .............................15 4.7. Error Handling ............................................15 4.8. Content URLs ..............................................16 5. CI/T Object Properties and Encoding ............................17 5.1. CI/T Objects ..............................................17 5.1.1. CI/T Commands ......................................17 5.1.2. Trigger Status Resources ...........................18 5.1.3. Trigger Collections ................................20 5.2. Properties of CI/T Objects ................................21 5.2.1. Trigger Specification ..............................21 5.2.2. Trigger Type .......................................23 5.2.3. Trigger Status .....................................24 5.2.4. PatternMatch .......................................24 5.2.5. Absolute Time ......................................25 5.2.6. Error Description ..................................26 5.2.7. Error Code .........................................26 6. Examples .......................................................27 6.1. Creating Triggers .........................................28 6.1.1. Preposition ........................................28 6.1.2. Invalidate .........................................30 6.2. Examining Trigger Status ..................................32 6.2.1. Collection of All Triggers .........................32 6.2.2. Filtered Collections of Trigger Status Resources ...33 6.2.3. Individual Trigger Status Resources ................34 6.2.4. Polling for Changes in Status ......................36 6.2.5. Deleting Trigger Status Resources ..................38 6.2.6. Error Reporting ....................................39
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   7. IANA Considerations ............................................40
      7.1. CDNI Payload Type Parameter Registrations .................40
      7.2. "CDNI CI/T Trigger Types" Registry ........................41
      7.3. "CDNI CI/T Error Codes" Registry ..........................41
   8. Security Considerations ........................................41
      8.1. Authentication, Authorization, Confidentiality,
           Integrity Protection ......................................42
      8.2. Denial of Service .........................................43
      8.3. Privacy ...................................................44
   9. References .....................................................44
      9.1. Normative References ......................................44
      9.2. Informative References ....................................45
   Appendix A. Formalization of the JSON Data ........................47
   Acknowledgments ...................................................49
   Authors' Addresses ................................................49

1. Introduction

[RFC6707] introduces the problem scope for Content Delivery Network Interconnection (CDNI) and lists the four categories of interfaces that may be used to compose a CDNI solution (Control, Metadata, Request Routing, and 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/T 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 downstream CDN. o Section 5 lists properties of CI/T Commands and Status Resources. o Section 6 contains example messages.
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1.1. Terminology

This document reuses the terminology defined in [RFC6707] and uses "uCDN" and "dCDN" as shorthand for "upstream CDN" and "downstream CDN", respectively. 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].

2. Model for CDNI Triggers

A 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 Commands: CI/T Trigger Commands and CI/T Cancel Commands. The CI/T Cancel Command can be used to request cancellation of an earlier CI/T Trigger Command. A CI/T Trigger Command is of one of the following 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 reusing it. o purge - used to instruct the dCDN to delete specific metadata or content. The CI/T interface is a web service offered by the dCDN. It allows CI/T Commands to be issued and allows triggered activity to be tracked. The CI/T interface builds on top of HTTP/1.1 [RFC7230]. References to URL in this document relate to HTTP/HTTPS URIs, as defined in Section 2.7 of [RFC7230]. When the dCDN accepts a CI/T Command, it creates a resource describing the status of the triggered activity -- a Trigger Status Resource. The uCDN can poll Trigger Status Resources to monitor progress. The dCDN maintains at least one collection of Trigger Status Resources for each uCDN. Each uCDN only has access to its own collections, the locations of which are shared when CDNI is established.
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   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 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 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 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 https://dcdn.example.com/triggers/uCDN    |
      [ ] --------------------------------------------------> [ ]--+
       |                                                      [ ]  | (2)
       |    (3) HTTP 201 Response                             [ ]<-+
      [ ] <-------------------------------------------------- [ ]
       |     Loc: https://dcdn.example.com/triggers/uCDN/123   |
       |                                                       |
       .                           .                           .
       .                           .                           .
       .                           .                           .
       |                                                       |
       |   (4) GET https://dcdn.example.com/triggers/uCDN/123  |
      [ ] --------------------------------------------------> [ ]
       |                                                      [ ]
       |   (5) HTTP 200 Trigger Status Resource               [ ]
      [ ] <-------------------------------------------------- [ ]
       |                                                       |
       |                                                       |

              Figure 1: Basic CDNI Message Flow for Triggers
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   The steps in Figure 1 are as follows:

   1.  The uCDN triggers action in the dCDN by POSTing a CI/T Command to
       a collection of Trigger Status Resources --
       "https://dcdn.example.com/triggers/uCDN".  This URL was given to
       the uCDN when the CI/T interface was established.

   2.  The dCDN authenticates the request, validates the 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 poll, possibly repeatedly, the Trigger Status
       Resource in the dCDN.

   5.  The dCDN responds with the Trigger Status Resource, describing
       the progress or results of the 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 CI/T Commands is under the dCDN's control, including its start time and pacing of the activity in the network. CI/T "invalidate" and "purge" commands MUST be applied to all data acquired before the command was accepted by the dCDN. The dCDN SHOULD NOT apply CI/T "invalidate" and "purge" commands to data acquired after 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 and then immediately pre-position replacement content at the same URLs, it SHOULD ensure that the dCDN has completed the invalidate/purge before initiating the pre-positioning. 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.
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2.2. Scope of Triggered Activity

Each 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.

2.2.1. Multiple Interconnected CDNs

In a network of interconnected CDNs, a single uCDN will originate a given item of metadata and associated content. It may distribute that metadata and content to more than one dCDN, which may in turn distribute that metadata and content to CDNs located further downstream. An intermediate CDN is a dCDN that passes on CDNI Metadata and content to dCDNs located further downstream. A "diamond" configuration is one where a dCDN can acquire metadata and content originated in one uCDN from that uCDN itself and an intermediate CDN, or via more than one intermediate CDN. CI/T Commands originating in the single source uCDN affect metadata and content in all dCDNs; however, in a diamond configuration, it may not be possible for the dCDN to determine which uCDN it acquired content from. In this case, a dCDN MUST allow each uCDN from which it may have acquired the content to act upon that content using CI/T Commands. In all other cases, a dCDN MUST reject CI/T Commands from a uCDN that attempts to act on another uCDN's content by using, for example, HTTP 403 ("Forbidden"). Security considerations are discussed further in Section 8. The diamond configuration may lead to inefficient interactions, but the interactions are otherwise harmless. For example: o When the uCDN issues an "invalidate" CI/T Command, a dCDN will receive that command from multiple directly connected uCDNs. The dCDN may schedule multiple such commands separately, and the last scheduled command may affect content already revalidated following execution of the "invalidate" command that was scheduled first.
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   o  If one of a dCDN's directly connected uCDNs loses its rights to
      distribute content, it may issue a CI/T "purge" command.  That
      purge may affect content the dCDN could retain because it's
      distributed by another directly connected uCDN.  But, that content
      can be reacquired by the dCDN from the remaining uCDN.

   o  When the uCDN originating an item of content issues a CI/T purge
      followed by a pre-position, two directly connected uCDNs will pass
      those commands to a dCDN.  That dCDN implementation need not merge
      those operations or notice the repetition, in which case the purge
      issued by one uCDN will complete before the other.  The first uCDN
      to finish its purge may then forward the "preposition" trigger,
      and content pre-positioned as a result might be affected by the
      still-running purge issued by the other uCDN.  However, the dCDN
      will reacquire that content as needed, or when it's asked to
      pre-position the content by the second uCDN.  A dCDN
      implementation could avoid this interaction by knowing which uCDN
      it acquired the content from, or it could minimize the
      consequences by recording the time at which the
      "invalidate"/"purge" command was received and not applying it to
      content acquired after that time.

2.3. Trigger Results

Possible states for a Trigger Status Resource are defined in Section 5.2.3. The CI/T Trigger Command MUST NOT be reported as "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 details, see Section 4.7. If a dCDN is also acting as a uCDN in a cascade, it MUST forward CI/T Commands to any dCDNs that may be affected. The CI/T Trigger Command MUST NOT be reported as "complete" in a CDN until it is "complete" in all of its dCDNs. If a CI/T Trigger Command is reported as "processed" in any dCDN, intermediate CDNs MUST NOT report "complete"; instead, they MUST also report "processed". A CI/T Command MAY be reported as "failed" as soon as it fails in a CDN or in any of its dCDNs. A canceled 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.
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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 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 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 and by filtering the response based on the uCDN with which the HTTP client 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 MAY also maintain collections representing filtered views of the collection of all Trigger Status Resources. These filtered collections are "optional-to-implement", but if they are implemented, the dCDN MUST include links to them in the collection of all Trigger Status Resources. The filtered collections are: o Pending - Trigger Status Resources for CI/T Trigger Commands that have been accepted but not yet acted upon. o Active - Trigger Status Resources for CI/T Trigger Commands that are currently being processed in the dCDN. o Complete - Trigger Status Resources representing activity that completed successfully, and "processed" CI/T Trigger Commands for which no further status updates will be made by the dCDN. o Failed - Trigger Status Resources representing CI/T Commands that failed or were canceled by the uCDN.
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4. CDNI Trigger Interface

This section describes an interface to enable a uCDN to trigger activity in a dCDN. 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. 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 CI/T Trigger Command is accepted by the dCDN, the dCDN creates a new Trigger Status Resource and returns its URI to the 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, 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 by the uCDN, so dCDNs are free to assign whatever structure they desire to the URIs for 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.
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4.1. Creating Triggers

To issue a 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, as described in Section 5.1.1. The dCDN validates the CI/T Command. If the command is malformed or the uCDN does not have sufficient access rights, the dCDN MUST either respond with an appropriate 4xx HTTP error code and not create a Trigger Status Resource or create a "failed" Trigger Status Resource containing an appropriate Error Description. When a CI/T Trigger Command is accepted, the uCDN MUST create a new Trigger Status Resource that 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 [RFC7231]. The HTTP response SHOULD include the content of the newly created Trigger Status Resource. This is particularly important in cases where the CI/T Trigger Command has completed immediately. Once a Trigger Status Resource has been created, the dCDN MUST NOT reuse its URI, even after that Trigger Status Resource has been removed. The dCDN SHOULD track and report on the progress of CI/T Trigger Commands using a Trigger Status Resource (Section 5.1.2). If the dCDN is not able to 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 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 pre-positioning after an earlier delete of the same URLs is expected to have finished. If the dCDN is able to track the execution of 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 processing has started, the status MUST be "active". Finally, once the CI/T Command is complete, the status MUST be set to "complete" or "failed".
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   A 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 "preposition" request for data that it has
   already acquired and that 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 Trigger Status Resources.

   Once created, Trigger Status Resources can be canceled 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 -- for example, 405 ("Method Not
   Allowed").

4.2. Checking Status

The uCDN has two ways to check the progress of CI/T Commands it has issued to the dCDN, as described in Sections 4.2.1 and 4.2.2. To allow the uCDN to check for changes in the status of a Trigger Status Resource or collection of Trigger Status Resources without refetching the whole resource or collection, the dCDN SHOULD include entity-tags (ETags) 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 that 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 the status of all 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 ETags to monitor for change, rather than repeatedly fetching the whole collection. An example of this is given in Section 6.2.4.
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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 Trigger Status Resource at any time. This can be used to retrieve progress information and to fetch the result of the CI/T Command. When polling in this way, the uCDN SHOULD use HTTP ETags to monitor for change, rather than repeatedly fetching the Trigger Status Resource.

4.3. Canceling Triggers

The uCDN can request cancellation of a CI/T Trigger Command by POSTing a CI/T Cancel Command to the collection of all Trigger Status Resources. The dCDN is required to accept and respond to the CI/T Cancel Command, but the actual cancellation of a CI/T Trigger Command is optional-to-implement. The dCDN MUST respond to the CI/T Cancel Command appropriately -- for example, with HTTP status code 200 ("OK") if the cancellation has been processed and the CI/T Command is inactive, 202 ("Accepted") if the command has been accepted but the CI/T Command remains active, or 501 ("Not Implemented") 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 the processing of that activity. Issuing a CI/T Cancel Command for a "pending" Trigger Status Resource does not, however, guarantee that the corresponding activity 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 CI/T Command. However, as with cancellation of a "pending" CI/T Command, the dCDN does not guarantee this. If the CI/T Command cannot be stopped immediately, the status in the corresponding Trigger Status Resource MUST be set to "cancelling", and the Trigger Status Resource MUST remain in the collection of Trigger Status Resources for active CI/T Commands. If processing is stopped before normal completion, the status value in the Trigger
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   Status Resource MUST be set to "cancelled", and the Trigger Status
   Resource MUST be included in the collection of failed CI/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 Trigger Status Resource SHOULD be rejected by the dCDN with an HTTP error. If a "pending" Trigger Status Resource is deleted, the dCDN SHOULD NOT start the processing of that activity. Deleting a "pending" 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 SHOULD stop processing the CI/T Command. However, as with deletion of a "pending" 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 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 Trigger Status Resource and respond to subsequent requests for it with an HTTP error. If the dCDN does remove Trigger Status Resources automatically, it MUST report the length of time after which it will do so, using a property of the collection of all Trigger Status Resources. It is
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   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 that it is able to get the status of its Trigger Status
   Resources for completed and failed CI/T Commands, it is RECOMMENDED
   that the 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 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 (PID) to uniquely identify itself. In every CI/T Command it originates or cascades, each CDN MUST append an array element containing its CDN PID to a JSON array under an entry named "cdn-path". When receiving CI/T Commands, a dCDN MUST check the cdn-path and reject any CI/T Command that already contains its own CDN PID 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 the cdn-path. The CDN PID consists of the two characters "AS" followed by the CDN provider's Autonomous System number [RFC1930], 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 ASes, the same AS number SHOULD be used in all messages from that CDN provider, unless there are multiple distinct CDNs. If the CDNI Request Routing Redirection interface (RI) described in [RFC7975] is implemented by the dCDN, the CI/T interface and the RI SHOULD use the same CDN PID.

4.7. Error Handling

A dCDN can signal rejection of a CI/T Command using HTTP status codes -- for example, 400 ("Bad Request") if the request is malformed, or 403 ("Forbidden") or 404 ("Not Found") if the uCDN does not have permission to issue CI/T Commands or it is trying to act on another CDN's data.
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   If any part of the 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 Status
   Resource is still "pending" or "active", if the 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 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 CI/T Command is abandoned by the dCDN, the dCDN SHOULD
      report an error.

   o  A CI/T "invalidate" 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" 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 Status Resource in
      state "pending" or "active" until either the CI/T Command is acted
      upon or the uCDN chooses to cancel it.

4.8. Content URLs

If content URLs are transformed by an intermediate CDN in a cascade, that intermediate CDN MUST similarly transform URLs in CI/T 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 a CI/T "invalidate" or "purge" command, content MUST be invalidated or purged regardless of the protocol clients used to request it.
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5. CI/T Object Properties and Encoding

The CI/T Commands, Trigger Status Resources, and Trigger Collections, as well as their properties, are encoded using JSON, as defined in Sections 5.1.1, 5.1.2, and 5.1.3. They MUST use the MIME media type "application/cdni", with parameter "ptype" values as defined below and in Section 7.1. Names in JSON are case sensitive. The names and literal values specified in the present document MUST always use lowercase. JSON types, including "object", "array", "number", and "string", are defined in [RFC7159]. Unrecognized name/value pairs in JSON objects SHOULD NOT be treated as an error by either the uCDN or dCDN. They SHOULD be ignored during processing and passed on by the 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. The encoding of values used by these objects is described in Section 5.2.

5.1.1. CI/T Commands

CI/T Commands MUST use a MIME media type of "application/cdni; ptype=ci-trigger-command". 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.
Top   ToC   RFC8007 - Page 18
      Name: cancel

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

         Value: A non-empty 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 PIDs of CDNs that have already issued the
         CI/T Command to their dCDNs.

         Value: A non-empty JSON array of JSON strings, where each
         string is a CDN PID as defined in Section 4.6.

         Mandatory: Yes.

5.1.2. Trigger Status Resources

Trigger Status Resources MUST use a MIME media type of "application/cdni; ptype=ci-trigger-status". 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 this need not be a byte-for-byte copy. For example, in the JSON representation the dCDN may re-serialize the information differently. Value: A Trigger Specification, as defined in Section 5.2.1. Mandatory: Yes.
Top   ToC   RFC8007 - Page 19
      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 synchronize 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 synchronize 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 synchronize 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.
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      Name: errors

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

         Value: An array of Error Descriptions, as defined in
         Section 5.2.6.  An empty array is allowed and is equivalent to
         omitting "errors" from the object.

         Mandatory: No.

5.1.3. Trigger Collections

Trigger Collections MUST use a MIME media type of "application/cdni; ptype=ci-trigger-collection". 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 zero or more 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 Trigger Status Resource and all references to it from collections. Value: A JSON number, which must be a positive integer, representing 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.
Top   ToC   RFC8007 - Page 21
      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 PID of the dCDN.

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

         Mandatory: Only in the collection of all Trigger Status
         Resources, if the dCDN implements the 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 its implementation of filtered 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 unrecognized 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: Defines the type of the CI/T Trigger Command. Value: Trigger Type, as defined in Section 5.2.2. Mandatory: Yes.
Top   ToC   RFC8007 - Page 22
      Name: metadata.urls

         Description: The uCDN URLs of the metadata the 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 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 [RFC8006].

         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 PatternMatch objects, 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 Trigger Type is "preposition".
Top   ToC   RFC8007 - Page 23
      Name: content.patterns

         Description: The content data the trigger applies to.

         Value: A JSON array of PatternMatch objects, 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 Trigger Type is "preposition".

5.2.2. Trigger Type

Trigger Type is used in a Trigger Specification to describe trigger action. All trigger types MUST be registered in the IANA "CDNI CI/T Trigger Types" registry (see Section 7.2). A dCDN receiving a request containing a trigger type it does not recognize or does not support MUST reject the request by creating a Trigger Status Resource with a status of "failed" and the "errors" array containing an Error Description with error "eunsupported". The following trigger types are defined by this document: +-------------+-----------------------------------------------------+ | 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 | | | revalidating 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 (the | | | dCDN should reacquire the metadata or content from | | | the uCDN if it needs it). | +-------------+-----------------------------------------------------+
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5.2.3. Trigger Status

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

5.2.4. PatternMatch

A PatternMatch consists of a string pattern to match against a URI, 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 URI matching. Value: A JSON string representing the pattern. The pattern can contain the wildcards * and ?, where * matches any sequence of [RFC3986] pchar or "/" characters (including the empty string) and ? matches exactly one [RFC3986] pchar character. The three literals $, * and ? MUST be escaped as $$, $* and $? (where $ is the designated escape character). All other characters are treated as literals. Mandatory: Yes.
Top   ToC   RFC8007 - Page 25
      Name: case-sensitive

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

         Value: One of the JSON values "true" (the matching is case
         sensitive) or "false" (the matching is case insensitive).

         Mandatory: No; default is case-insensitive match.

      Name: match-query-string

         Description: Flag indicating whether to include the query part
         of the URI when comparing against the pattern.

         Value: One of the JSON values "true" (the full URI, including
         the query part, should be compared against the given pattern)
         or "false" (the query part of the URI should be dropped before
         comparison with the given pattern).

         Mandatory: No; default is "false".  The query part of the URI
         should be dropped before comparison with the given pattern.

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

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

5.2.5. Absolute Time

A JSON number, seconds since the UNIX epoch (00:00:00 UTC on 1 January 1970).
Top   ToC   RFC8007 - Page 26

5.2.6. Error Description

An Error Description is used to report the failure of a CI/T Command or failure in the activity it triggered. It is encoded as a JSON object with the following name/value pairs: 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 generalize the URLs. (For example, if the uCDN requests pre-positioning of URLs "https://content.example.com/a" and "https://content.example.com/b", the dCDN must not generalize its error report to the pattern "https://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. All Error Codes MUST be registered in the IANA "CDNI CI/T Error Codes" registry (see Section 7.3). Unknown Error Codes MUST be treated as fatal errors, and the request MUST NOT be automatically retried without modification.
Top   ToC   RFC8007 - Page 27
   The following Error Codes are defined by this document and MUST be
   supported by an implementation of the CI/T interface.

   +--------------+----------------------------------------------------+
   | Error Code   | Description                                        |
   +--------------+----------------------------------------------------+
   | emeta        | The dCDN was unable to acquire metadata required   |
   |              | to fulfill the request.                            |
   | econtent     | The dCDN was unable to acquire content (CI/T       |
   |              | "preposition" commands only).                      |
   | eperm        | The uCDN does not have permission to issue the     |
   |              | CI/T Command (for example, the data is owned by    |
   |              | another CDN).                                      |
   | ereject      | The dCDN is not willing to fulfill the CI/T        |
   |              | Command (for example, a "preposition" request for  |
   |              | content at a time when the dCDN would not accept   |
   |              | Request Routing requests from the uCDN).           |
   | ecdn         | An internal error in the dCDN or one of its dCDNs. |
   | ecanceled    | The uCDN canceled the request.                     |
   | eunsupported | The Trigger Specification contained a "type" that  |
   |              | is not supported by the dCDN.  No action was taken |
   |              | by the dCDN other than to create a Trigger Status  |
   |              | Resource in state "failed".                        |
   +--------------+----------------------------------------------------+



(page 27 continued on part 2)

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