RFC 8007

RFC 8007: Content Delivery Network Interconnection (CDNI) Control Interface / Triggers 🎀

okay bestie, this is the title block 💅

• Series: Internet Engineering Task Force (IETF) 🌸
• Request for Comments: 8007 ✨
• Authors: R. Murray and B. Niven-Jenkins, both at Nokia 🫶
• Category: Standards Track (so it's an actual Internet standard, not just a suggestion 👑)
• ISSN: 2070-1721
• Date: December 2016 🎄
• Obsoletes / Updates: nothing listed in the title block 🦋

---

Abstract 🌸

so this doc is about the bit of the Content Delivery Network Interconnection (CDNI) Control interface that lets one CDN trigger stuff in another CDN that's delivering content on its behalf 🧚. the upstream CDN can ask the downstream CDN to pre-position metadata or content, or to invalidate or purge metadata or content 💖. and the upstream CDN can keep an eye on how that triggered activity is going in the downstream CDN 👀. main character energy, honestly 💅

Status of This Memo 📜

this is an Internet Standards Track document 🔥

it's a product of the Internet Engineering Task Force (IETF) and it represents the consensus of the IETF community 🫶. it got public review and was approved for publication by the Internet Engineering Steering Group (IESG) ✨. if you want more info on Internet Standards, check Section 2 of RFC 7841 🌈

for the current status of this document, any errata, and how to send feedback, go to 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) as in effect on the date of publication 📚. please actually read these, bestie, because they explain your rights and restrictions for this doc 🙈. code components pulled out of this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come 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 ................................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

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 ✨

okay so [RFC6707] sets up the problem scope for Content Delivery Network Interconnection (CDNI) and lists the four categories of interfaces that may be used to put a CDNI solution together: Control, Metadata, Request Routing, and Logging 🧩

then [RFC7336] builds on [RFC6707] and goes deeper into each interface and how they relate to each other 🦋

this document is all about the "CI/T" interface, which is "CDNI Control interface / Triggers" 💖. it doesn't cover the parts of the Control interface about configuration, bootstrapping, or authentication of CDN Interconnect interfaces 🙈. Section 4 of [RFC7337] lists the requirements specific to the CI/T interface, and the ones that apply to it are CI-1 to CI-6 🔥

here's the vibe of the rest of the doc:

• Section 2 gives the high-level model for the CI/T interface 🌈
• Section 3 covers collections of Trigger Status Resources 🎀
• Section 4 defines the web service the downstream CDN provides 🧚
• Section 5 lists the properties of CI/T Commands and Status Resources 💅
• Section 6 has example messages 🍓

1.1. Terminology 📚

this doc reuses the terminology from [RFC6707], and it 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] 🔐 (these are the official requirement words, so they keep their exact meaning, no vibes-based interpretation allowed 💀)

2. Model for CDNI Triggers ✨

okay so bestie, a CI/T Command is basically the uCDN asking the dCDN to go do some work on data tied to content requests that came from the uCDN 💅

There are two kinds of CI/T Commands: CI/T Trigger Commands and CI/T Cancel Commands. The Cancel one is how you ask to stop an earlier Trigger Command 🛑 A CI/T Trigger Command is one of these three types:

• preposition - used to instruct the dCDN to fetch metadata from the uCDN, or content from any origin including the uCDN. 🚚
• invalidate - used to instruct the dCDN to revalidate specific metadata or content before reusing it. 🔍
• purge - used to instruct the dCDN to delete specific metadata or content. 🗑️

The CI/T interface is a web service run by the dCDN 🌐 It's where CI/T Commands get issued and where you can track what they triggered. It's built on top of HTTP/1.1 [RFC7230]. When this document says URL, it means HTTP/HTTPS URIs, same as Section 2.7 of [RFC7230] 🦋

When the dCDN accepts a CI/T Command, it makes a resource that shows the status of the triggered activity, called a Trigger Status Resource 📊 The uCDN can poll Trigger Status Resources to see how things are going.

The dCDN keeps at least one collection of Trigger Status Resources for each uCDN 🗂️ Each uCDN can only see its own collections, and the locations get shared when CDNI is set up. Very private, very iconic 🔒

To trigger something, the uCDN POSTs a CI/T Command to the collection of Trigger Status Resources. If the dCDN says yes, it makes a brand-new Trigger Status Resource and sends back its location ✨ To check progress, the uCDN can GET that Trigger Status Resource. Want to cancel a CI/T Trigger Command? The uCDN can POST to the collection of Trigger Status Resources, or just delete the Trigger Status Resource 🙈

On top of the full collection of Trigger Status Resources for the uCDN, the dCDN can also keep filtered views 💜 Those are defined in Section 3, and they include collections for active and completed CI/T Trigger Commands. They're super handy when you want to poll the status of a bunch of jobs at once 🎀

Here's Figure 1, the basic message flow for the uCDN triggering activity in the dCDN and then checking on it. Only the successful path is shown, and examples of the actual messages are 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 🦋

So the steps in Figure 1 go like this 👀

1. The uCDN triggers action in the dCDN by POSTing a CI/T Command to a collection of Trigger Status Resources, which is https://dcdn.example.com/triggers/uCDN. The uCDN got this URL when the CI/T interface was set up 🔑
2. The dCDN authenticates the request, validates the CI/T Command, and if it accepts, makes a new Trigger Status Resource 🛡️
3. The dCDN replies to the uCDN with an HTTP 201 response status and the location of the Trigger Status Resource 📮
4. The uCDN can poll the Trigger Status Resource in the dCDN, and it can do that again and again if it wants 🔁
5. The dCDN responds with the Trigger Status Resource, which describes the progress or results of the CI/T Trigger Command 📈

The rest of this document goes deeper on the messages, Trigger Status Resources, and collections of Trigger Status Resources 🧚

---

2.1. Timing of Triggered Activity

Timing of CI/T Command execution is totally up to the dCDN 🕰️ That includes when things start and how the activity gets paced across 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. 😬

Real talk: the uCDN can't count on the dCDN skipping newer data. Don't build your whole plan around that one 🙃

If the uCDN wants 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). That's the classic race-condition plot twist 💀

Because the dCDN controls CI/T Command timing, the dCDN implementation gets to choose whether it applies CI/T "invalidate" and "purge" commands to content acquisition that already started when the command came in 🎛️

---

2.2. Scope of Triggered Activity

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

Multiple representations of an HTTP resource can share the same URL 🎨 CI/T Trigger Commands that invalidate or purge metadata or content apply to all resource representations with matching URLs. So one command can hit a whole bunch of versions at once 💥

2.2.1. Multiple Interconnected CDNs

In a network of interconnected CDNs, one uCDN originates a given item of metadata and its associated content 🌐 That uCDN can distribute the metadata and content to more than one dCDN, and those dCDNs can pass it further downstream to other CDNs 🌊

An intermediate CDN is a dCDN that passes CDNI Metadata and content on to dCDNs further downstream 🔗

A "diamond" configuration is when a dCDN can acquire metadata and content that started in one uCDN, either straight from that uCDN or through an intermediate CDN, or through more than one intermediate CDN 💎

CI/T Commands from the single source uCDN affect metadata and content in all dCDNs. But in a diamond configuration, the dCDN might not be able to figure out which uCDN it got the content from 🤷‍♀️ In that case, a dCDN MUST allow each uCDN it may have acquired the content from to act on that content using CI/T Commands.

In all other cases, a dCDN MUST reject CI/T Commands from a uCDN that tries to act on another uCDN's content, for example with HTTP 403 ("Forbidden") 🚫 Nobody touches somebody else's stuff, periodt 💅

Security considerations are covered in more detail in Section 8 🔐

The diamond configuration can lead to inefficient interactions, but they're otherwise harmless. For example:

• 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. 🔁
• 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. 🔄
• 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. 🌊✨

3. Collections of Trigger Status Resources 🗂️

Okay so, like we talked about in Section 2, Trigger Status Resources live in the dCDN so they can keep everyone posted on the activity each uCDN triggered 👀

A collection of Trigger Status Resources is basically a resource that holds a reference to every Trigger Status Resource in that collection. It's like a little playlist of links 🎀

The dCDN MUST make a collection of a uCDN's Trigger Status Resources available to that uCDN. This collection has everything created for CI/T Commands from that uCDN that the dCDN accepted, and that the uCDN hasn't deleted yet, or that the dCDN hasn't expired and removed (as described in Section 4.4). Trigger Status Resources belonging to a uCDN MUST NOT be visible to any other CDN. Not me, not sharing your stuff 🙅‍♀️ For example, the dCDN could do this by giving each uCDN its own collection URL and filtering the response based on which uCDN the HTTP client is connected with 💅

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. Simple as that 🫶

Now, so the uCDN can check on a bunch of jobs in one request, the dCDN MAY also keep collections that are filtered views of the collection of all Trigger Status Resources. These filtered collections are "optional-to-implement," but if the dCDN does build them, it MUST include links to them in the collection of all Trigger Status Resources. The filtered collections are:

• Pending - Trigger Status Resources for CI/T Trigger Commands that have been accepted but not yet acted upon ⏳
• Active - Trigger Status Resources for CI/T Trigger Commands that are currently being processed in the dCDN 🔥
• Complete - Trigger Status Resources representing activity that completed successfully, plus processed CI/T Trigger Commands for which the dCDN will make no further status updates ✨
• Failed - Trigger Status Resources representing CI/T Commands that failed or were canceled by the uCDN 💀

---

4. CDNI Trigger Interface 🦋

This section describes an interface that lets a uCDN trigger activity in a dCDN. It's giving protocol 🌸

The CI/T interface is built on top of HTTP, so dCDNs can make use of any HTTP feature when they implement the CI/T interface. For example, a dCDN SHOULD make use of HTTP's caching mechanisms to indicate that a requested response or representation has not been modified. That way the uCDN doesn't have to do as much work figuring out 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. Both sides need to speak it, bestie 🤝

The URL of the dCDN's collection of all Trigger Status Resources needs to be either discovered by the uCDN or configured in it. How the discovery happens is outside the scope of this document, so that's a different story 🗺️

CI/T Commands are POSTed to the dCDN's collection of all Trigger Status Resources. If the dCDN accepts a CI/T Trigger Command, it creates a new Trigger Status Resource and sends its URI back to the uCDN in an HTTP 201 response. After that, the uCDN can keep an eye on the triggered activity using that resource and the collections described in Section 3 👀✨

The URI of each Trigger Status Resource gets returned to the uCDN when it's created, and the URIs of all Trigger Status Resources are listed in the dCDN's collection of all Trigger Status Resources. So the uCDN can discover every single one, which means dCDNs are free to structure their CI/T URIs however they like 🎨 That's why uCDNs MUST NOT make any assumptions about the structure of CI/T URIs or how CI/T objects map to their URIs. The URIs in this document's examples are purely illustrative and are not meant to force a particular structure on CI/T implementations 🙈

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 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 doesn't 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. Rejected, but make it make sense 💅

When a CI/T Trigger Command is accepted, the uCDN MUST create a new Trigger Status Resource that conveys 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 matters most when the CI/T Trigger Command has already completed immediately, so it's a big deal ⚡

Once a Trigger Status Resource has been created, the dCDN MUST NOT reuse its URI, even after that Trigger Status Resource has been removed. No recycling URIs, ever 🙅‍♀️

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 can't do that, it MUST indicate that it accepted the request but won't 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 carry on as it would 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 give an estimated completion time for the request using the etime property of the Trigger Status Resource. This lets the uCDN schedule pre-positioning for after an earlier delete of the same URLs is expected to have finished ⏰

If the dCDN can track the execution of CI/T Commands and a CI/T Command gets queued 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 🏁

A CI/T Trigger Command might result in no activity in the dCDN at all. For example, that happens with an invalidate or purge request for data the dCDN hasn't acquired yet, or a preposition request for data it already has 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. Nothing to do, but still acknowledged 🌈

Once created, Trigger Status Resources can be canceled or deleted by the uCDN, but they can't be 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 on the progress of CI/T Commands it has issued to the dCDN, as described in Sections 4.2.1 and 4.2.2 🧚

To let the uCDN check for changes in the status of a Trigger Status Resource or a collection of them without refetching the whole thing, 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 on responses to GETs for Trigger Status Resources and Collections to indicate how often it recommends the uCDN poll for changes 🕰️

4.2.1. Polling Trigger Status Resource Collections 🧺

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

This makes it possible to poll the status of every CI/T Trigger Command in a single request. If the dCDN moves a Trigger Status Resource from the active collection to the completed one, the uCDN can fetch the result of that activity 🎉

When polling this way, the uCDN SHOULD use HTTP ETags to watch for changes, rather than fetching the whole collection over and over. An example of this is given in Section 6.2.4 💜

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 this way, the uCDN SHOULD use HTTP ETags to watch for changes, 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 actually canceling a CI/T Trigger Command is optional-to-implement 🥺

The dCDN MUST respond to the CI/T Cancel Command appropriately. For example, it responds with HTTP status code 200 ("OK") if the cancellation has been processed and the CI/T Command is inactive, 202 ("Accepted") if the command was accepted but is still active, or 501 ("Not Implemented") if the dCDN doesn't support cancellation 🚦

If the dCDN accepts cancellation of a pending Trigger Status Resource, the dCDN SHOULD NOT start processing that activity. Still, issuing a CI/T Cancel Command for a pending Trigger Status Resource doesn't guarantee the corresponding activity won't start, because the uCDN can't control the timing of that activity. Processing could, for example, begin after the uCDN sends the POST but before the dCDN handles that request 😬

If the dCDN accepts cancellation of an active or processed Trigger Status Resource, the dCDN SHOULD stop processing the CI/T Command. But, just like with a pending CI/T Command, the dCDN doesn't guarantee that 🤷‍♀️

If the CI/T Command can't 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 stops before normal completion, the status value in the Trigger Status Resource MUST be set to cancelled, and the Trigger Status Resource MUST be included in the collection of failed CI/T Trigger Commands 🛑

Canceling a complete or failed Trigger Status Resource doesn't need any processing in the dCDN. Its status MUST NOT be changed to cancelled 🧊

4.4. Deleting Triggers ✨

okay so the uCDN can delete Trigger Status Resources whenever it wants 💅, using the HTTP DELETE method. It's kinda like cancelling, except after a delete there's no Trigger Status Resource left hanging around 🫧

once something is deleted, every reference to that Trigger Status Resource MUST be removed from all Trigger Status Resource collections 🧹. if anyone tries to GET it later, the dCDN SHOULD reject that with an HTTP error 🙅‍♀️

if a "pending" Trigger Status Resource gets deleted, the dCDN SHOULD NOT start processing that activity 🛑. BUT deleting a "pending" one does not guarantee it hasn't started already 😭, because the uCDN can't control the timing of that activity. for example, processing could kick off after the uCDN sends the DELETE but before the dCDN actually handles that request. not me getting caught in a timing gap 💀

if an "active" or "processed" Trigger Status Resource is deleted, the dCDN SHOULD stop processing the CI/T Command. however, just like with a "pending" one, the dCDN doesn't guarantee this 🫶

deleting a "complete" or "failed" Trigger Status Resource requires no processing in the dCDN other than deleting the Trigger Status Resource itself. easy breezy 🌸

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" 🍓. when that happens, the dCDN removes the Trigger Status Resource and answers any later 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. no hiding the timer, bestie 🙈

it is 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" 🌈 that's the vibe the spec is going for.

to make sure the uCDN can still check on 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. timing is everything ⏰✨

4.6. Loop Detection and Prevention 🔁

okay picture this: three CDNs, A, B, and C. if CDNs B and C keep handing CDN A's content back and forth to each other, CDN A's CI/T Commands could get passed between B and C in a loop 😵‍💫. more complicated networks of CDNs could have similar loops with more hops. a whole spiral situation 🌀

so to prevent and detect these 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 🛑. no going in circles, periodt 💅

the CDN PID is the two characters "AS" followed by the CDN provider's Autonomous System number [RFC1930], then a colon (":") and an additional qualifier 🎀. that qualifier exists 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 🦋

and 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. matching energy ✨

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 doesn't have permission to issue CI/T Commands or it's trying to act on another CDN's data 👀. bad vibes, all of them 😤

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 is where the failed actions and their reasons get listed 📋. it can show up while the Trigger Status Resource is still "pending" or "active", if the CI/T Trigger Command is still running for some of the URLs or patterns in the Trigger Specification 🏃‍♀️

once a request has been accepted, processing errors get reported in the Trigger Status Resource as a list of Error Descriptions 📝. each Error Description reports 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 can't pass a CI/T Command on to any of its cascaded dCDNs, here's the breakdown 👇

• if the CI/T Command is abandoned by the dCDN, the dCDN SHOULD report an error.
• 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 🙅‍♀️ revalidate first, no shortcuts.
• 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 🔄
• 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 get transformed by an intermediate CDN in a cascade, that intermediate CDN MUST similarly transform URLs in the CI/T Commands it passes to its dCDN 🪄. consistency is iconic.

when processing Trigger Specifications, CDNs MUST ignore the URL scheme (HTTP or HTTPS) when 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. http or https, the content gets handled either way 🌈

---

5. CI/T Object Properties and Encoding 💜

the CI/T Commands, Trigger Status Resources, and Trigger Collections, plus all of 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 "ptype" parameter 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, no exceptions 🫶

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. so nothing gets dropped on the floor 🦋

5.1. CI/T Objects 🧩

the top-level objects defined by the CI/T interface are described in this section ✨. the encoding of the 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.
• 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.
• 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.
• 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 🎀

Okay bestie, Trigger Collections MUST use the MIME media type application/cdni; ptype=ci-trigger-collection 💅 no exceptions, no cap.

A Trigger Collection is encoded as a JSON object containing the following name/value pairs. Here's the whole lineup 🧚

• 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.
• staleresourcetime ⏳
  • Description: This is how long the dCDN promises to keep a completed Trigger Status Resource. After that time, the dCDN SHOULD delete the Trigger Status Resource and all references to it from collections. 💀 tea spill
  • 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.
• 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.
• 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 is where we spell out the values that can show up in the top-level objects from Section 5.1, plus how they get encoded. Let's gooo ✨

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.

• type 🔥
  • Description: Defines the type of the CI/T Trigger Command.
  • Value: Trigger Type, as defined in Section 5.2.2.
  • Mandatory: Yes.
• 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.
• 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.
• 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.
• 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".
• 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 the bit that lives inside a Trigger Specification and says what action the trigger is asking for. Main character energy 👑

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". 💀 that's a hard no, bestie.

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).                           |
+-------------+-----------------------------------------------------+

5.2.3. Trigger Status ✨

Trigger Status tells you how the triggered activity is doing right now. 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 is a string pattern you match against a URI, plus some flags that describe how the matching should go. 🧠 It's encoded as a JSON object with these name/value pairs:

• 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.
• 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.
• 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.

Here's an example of a case-sensitive prefix match against https://www.example.com/trailers/ 🎀

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

5.2.5. Absolute Time ⏰

It's a JSON number: seconds since the UNIX epoch (00:00:00 UTC on 1 January 1970). Time is a whole vibe 🌈

5.2.6. Error Description 💀

An Error Description is how we report that a CI/T Command failed, or that the activity it triggered failed. 🙈 It's encoded as a JSON object with these name/value pairs:

• error 🚨
  • Value: Error Code, as defined in Section 5.2.7.
  • Mandatory: Yes.
• 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.
• description 📝
  • Description: A human-readable description of the error.
  • Value: A JSON string, the human-readable description.
  • Mandatory: No.

⚠️ Bestie, don't generalize the URLs in your error reports. Copy them exactly as they came in or the whole report gets messy 💅

Okay that's the vibe for Section 5.2! 🍃

5.2.7. Error Code 🚨

okay so this type is how the dCDN tells the uCDN that something went wrong while processing a trigger 😭. Every Error Code 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 🙅‍♀️. no cap, that part is serious!!

These are the Error Codes this document defines, and every single one 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".                        |
+--------------+----------------------------------------------------+

---

6. Examples 🎀

okay the next bit is all examples 🧚 of different CI/T objects encoded as JSON, so you can see what they actually look like!!

Discovery of the CI/T interface is out of scope for 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. hard rule, bestie, don't go reading tea leaves in the URL 🚫

In the examples in this section, https://dcdn.example.com/triggers is the location of the collection of all Trigger Status Resources, and the CDN PID of the uCDN is AS64496:1 💜

6.1. Creating Triggers 🦋

This is the uCDN triggering activity in the dCDN, bestie:

6.1.1. Preposition 🌸

Here's a CI/T "preposition" command 💖, which is a POST to the collection of all Trigger Status Resources.

Note that metadata.patterns and content.patterns are not allowed in a pre-position Trigger Specification ⚠️.

REQUEST:

POST /triggers HTTP/1.1
User-Agent: example-user-agent/0.1
Host: dcdn.example.com
Accept: */*
Content-Type: application/cdni; ptype=ci-trigger-command
Content-Length: 352

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

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

RESPONSE:

HTTP/1.1 201 Created
Date: Wed, 04 May 2016 08:48:10 GMT
Content-Length: 467
Content-Type: application/cdni; ptype=ci-trigger-status
Location: https://dcdn.example.com/triggers/0
Server: example-server/0.1

{
    "ctime": 1462351690,
    "etime": 1462351698,
    "mtime": 1462351690,
    "status": "pending",
    "trigger": {
        "content.urls": [
            "https://www.example.com/a/b/c/1",
            "https://www.example.com/a/b/c/2",
            "https://www.example.com/a/b/c/3",
            "https://www.example.com/a/b/c/4"
        ],
        "metadata.urls": [
            "https://metadata.example.com/a/b/c"
        ],
        "type": "preposition"
    }
}

6.1.2. Invalidate 🧹

Next up is a CI/T "invalidate" command 💅, another POST to the collection of all Trigger Status Resources. This one tells the dCDN to revalidate the content at https://www.example.com/a/index.html, plus any metadata and content whose URLs are prefixed by https://metadata.example.com/a/b/ using case-insensitive matching, and https://www.example.com/a/b/ using case-sensitive matching, respectively. the matching rules are doing a lot here 🤓

REQUEST:

POST /triggers HTTP/1.1
User-Agent: example-user-agent/0.1
Host: dcdn.example.com
Accept: */*
Content-Type: application/cdni; ptype=ci-trigger-command
Content-Length: 387

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

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

    "content.urls": [ "https://www.example.com/a/index.html" ],
    "content.patterns": [
        { "pattern": "https://www.example.com/a/b/*",
          "case-sensitive": true
        }
      ]
  },
  "cdn-path": [ "AS64496:1" ]
}

RESPONSE:

HTTP/1.1 201 Created
Date: Wed, 04 May 2016 08:48:11 GMT
Content-Length: 545
Content-Type: application/cdni; ptype=ci-trigger-status
Location: https://dcdn.example.com/triggers/1
Server: example-server/0.1

{
    "ctime": 1462351691,
    "etime": 1462351699,
    "mtime": 1462351691,
    "status": "pending",
    "trigger": {
        "content.patterns": [
            {
                "case-sensitive": true,
                "pattern": "https://www.example.com/a/b/*"
            }
        ],
        "content.urls": [
            "https://www.example.com/a/index.html"
        ],
        "metadata.patterns": [
            {
                "pattern": "https://metadata.example.com/a/b/*"
            }
        ],
        "type": "invalidate"
    }
}

6.2. Examining Trigger Status 🔍

Once Trigger Status Resources exist, the uCDN can check their status like this 👀.

6.2.1. Collection of All Triggers 📚

The uCDN can fetch the collection of all Trigger Status Resources it has created that have not yet been deleted or removed as expired ✨. After creating the "preposition" and "invalidate" triggers from above, this collection might look like this:

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: 341
Expires: Wed, 04 May 2016 08:49:11 GMT
Server: example-server/0.1
ETag: "-936094426920308378"
Cache-Control: max-age=60
Date: Wed, 04 May 2016 08:48:11 GMT
Content-Type: application/cdni; ptype=ci-trigger-collection

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

6.2.2. Filtered Collections of Trigger Status Resources 🗂️

The filtered collections are available to the uCDN too 🫧. Before the dCDN starts processing the two CI/T Trigger Commands from above, both of them will show up 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: 152
Expires: Wed, 04 May 2016 08:49:11 GMT
Server: example-server/0.1
ETag: "4331492443626270781"
Cache-Control: max-age=60
Date: Wed, 04 May 2016 08:48:11 GMT
Content-Type: application/cdni; ptype=ci-trigger-collection

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

At this point, if no other Trigger Status Resources had been created, the other filtered views 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: 54
Expires: Wed, 04 May 2016 08:49:11 GMT
Server: example-server/0.1
ETag: "7958041393922269003"
Cache-Control: max-age=60
Date: Wed, 04 May 2016 08:48:11 GMT
Content-Type: application/cdni; ptype=ci-trigger-collection

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

6.2.3. Individual Trigger Status Resources 🔎

You can also look at the Trigger Status Resources for the details of individual CI/T Trigger Commands 🥰. Here they are for the CI/T "preposition" and "invalidate" commands from the earlier 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: 467
Expires: Wed, 04 May 2016 08:49:10 GMT
Server: example-server/0.1
ETag: "6990548174277557683"
Cache-Control: max-age=60
Date: Wed, 04 May 2016 08:48:10 GMT
Content-Type: application/cdni; ptype=ci-trigger-status

{
    "ctime": 1462351690,
    "etime": 1462351698,
    "mtime": 1462351690,
    "status": "pending",
    "trigger": {
        "content.urls": [
            "https://www.example.com/a/b/c/1",
            "https://www.example.com/a/b/c/2",
            "https://www.example.com/a/b/c/3",
            "https://www.example.com/a/b/c/4"
        ],
        "metadata.urls": [
            "https://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: 545
Expires: Wed, 04 May 2016 08:49:11 GMT
Server: example-server/0.1
ETag: "-554385204989405469"
Cache-Control: max-age=60
Date: Wed, 04 May 2016 08:48:11 GMT
Content-Type: application/cdni; ptype=ci-trigger-status
{
    "ctime": 1462351691,
    "etime": 1462351699,
    "mtime": 1462351691,
    "status": "pending",
    "trigger": {
        "content.patterns": [
            {
                "case-sensitive": true,
                "pattern": "https://www.example.com/a/b/*"
            }
        ],
        "content.urls": [
            "https://www.example.com/a/index.html"
        ],
        "metadata.patterns": [
            {
                "pattern": "https://metadata.example.com/a/b/*"
            }
        ],
        "type": "invalidate"
    }
}

6.2.4. Polling for Changes in Status ✨

okay so the uCDN SHOULD use the ETags of collections or Trigger Status Resources when it's polling for changes in status 🔄 here's how that looks bestie 💖

REQUEST:

GET /triggers/pending HTTP/1.1
User-Agent: example-user-agent/0.1
Host: dcdn.example.com
Accept: */*
If-None-Match: "4331492443626270781"

RESPONSE:

HTTP/1.1 304 Not Modified
Content-Length: 0
Expires: Wed, 04 May 2016 08:49:11 GMT
Server: example-server/0.1
ETag: "4331492443626270781"
Cache-Control: max-age=60
Date: Wed, 04 May 2016 08:48:11 GMT
Content-Type: application/cdni; ptype=ci-trigger-collection

REQUEST:

GET /triggers/0 HTTP/1.1
User-Agent: example-user-agent/0.1
Host: dcdn.example.com
Accept: */*
If-None-Match: "6990548174277557683"

RESPONSE:

HTTP/1.1 304 Not Modified
Content-Length: 0
Expires: Wed, 04 May 2016 08:49:10 GMT
Server: example-server/0.1
ETag: "6990548174277557683"
Cache-Control: max-age=60
Date: Wed, 04 May 2016 08:48:10 GMT
Content-Type: application/cdni; ptype=ci-trigger-status

Once the CI/T Trigger Command is complete, the contents of the filtered collections get updated along with their ETags 🎀 For example, once both example CI/T Trigger Commands are complete, the collections of pending and complete Trigger Status Resources might look like this 👀

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: 54
Expires: Wed, 04 May 2016 08:49:15 GMT
Server: example-server/0.1
ETag: "1337503181677633762"
Cache-Control: max-age=60
Date: Wed, 04 May 2016 08:48:15 GMT
Content-Type: application/cdni; ptype=ci-trigger-collection

{
    "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: 152
Expires: Wed, 04 May 2016 08:49:22 GMT
Server: example-server/0.1
ETag: "4481489539378529796"
Cache-Control: max-age=60
Date: Wed, 04 May 2016 08:48:22 GMT
Content-Type: application/cdni; ptype=ci-trigger-collection

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

---

6.2.5. Deleting Trigger Status Resources 🗑️

okay so the uCDN can delete completed and failed Trigger Status Resources to shrink the collections 🧹, as described in Section 4.4. For example, to delete the "preposition" request from the 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: Wed, 04 May 2016 08:48:22 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 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: 105
Expires: Wed, 04 May 2016 08:49:22 GMT
Server: example-server/0.1
ETag: "-6938620031669085677"
Cache-Control: max-age=60
Date: Wed, 04 May 2016 08:48:22 GMT
Content-Type: application/cdni; ptype=ci-trigger-collection

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

---

6.2.6. Error Reporting 🚨

okay this one is so real 😭 in this example the uCDN asked for pre-positioning of "https://newsite.example.com/index.html", but the dCDN couldn't find 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: 486
Expires: Wed, 04 May 2016 08:49:26 GMT
Server: example-server/0.1
ETag: "5182824839919043757"
Cache-Control: max-age=60
Date: Wed, 04 May 2016 08:48:26 GMT
Content-Type: application/cdni; ptype=ci-trigger-status

{
    "ctime": 1462351702,
    "errors": [
        {
            "content.urls": [
                "https://newsite.example.com/index.html"
            ],
            "description": "newsite.example.com not in HostIndex",
            "error": "emeta"
        }
    ],
    "etime": 1462351710,
    "mtime": 1462351706,
    "status": "active",
    "trigger": {
        "content.urls": [
            "https://newsite.example.com/index.html"
        ],
        "type": "preposition"
    }
}

---

7. IANA Considerations 🌸

7.1. CDNI Payload Type Parameter Registrations 🎀

The IANA is requested to register the following new Payload Types in the "CDNI Payload Types" registry defined by [RFC7736], for use with the "application/cdni" MIME media type.

+-----------------------+---------------+
| Payload Type          | Specification |
+-----------------------+---------------+
| ci-trigger-command    | RFC 8007      |
| ci-trigger-status     | RFC 8007      |
| ci-trigger-collection | RFC 8007      |
+-----------------------+---------------+

7.2. "CDNI CI/T Trigger Types" Registry 🧚

The IANA is requested to create a new "CDNI CI/T Trigger Types" subregistry under the "Content Delivery Network Interconnection (CDNI) Parameters" registry.

Additions to the "CDNI CI/T Trigger Types" registry will be made via the RFC Required policy as defined in [RFC5226].

The initial contents of the "CDNI CI/T Trigger Types" registry comprise the names and descriptions listed in Section 5.2.2 of this document, with this document acting as the specification.

7.3. "CDNI CI/T Error Codes" Registry 💜

The IANA is requested to create a new "CDNI CI/T Error Codes" subregistry under the "Content Delivery Network Interconnection (CDNI) Parameters" registry.

Additions to the "CDNI CI/T Error Codes" registry will be made via the Specification Required policy as defined in [RFC5226]. The Designated Expert will verify that new Error Code registrations do not duplicate existing Error Code definitions (in name or functionality), prevent gratuitous additions to the namespace, and prevent any additions to the namespace that would impair the interoperability of CDNI implementations.

The initial contents of the "CDNI CI/T Error Codes" registry comprise the names and descriptions of the Error Codes listed in Section 5.2.7 of this document, with this document acting as the specification.

---

8. Security Considerations 🔥

okay this section is SERIOUS bestie, read it all 🙈

The CI/T interface provides a mechanism to allow a uCDN to generate requests into the dCDN and to inspect its own CI/T requests and their current states. The CI/T interface does not allow access to, or modification of, the uCDN or dCDN metadata relating to content delivery or to the content itself. It can only control the presence of that metadata in the dCDN, and the processing work and network utilization involved in ensuring that presence.

By examining "preposition" requests to a dCDN, and correctly interpreting content and metadata URLs, an attacker could learn the uCDN's or content owner's predictions for future content popularity. By examining "invalidate" or "purge" requests, an attacker could learn about changes in the content owner's catalog.

By injecting CI/T Commands, an attacker or a misbehaving uCDN would generate work in the dCDN and uCDN as they process those requests. So would a man-in-the-middle attacker modifying valid CI/T Commands generated by the uCDN. In both cases, that would decrease the dCDN's caching efficiency by causing it to unnecessarily acquire or reacquire content metadata and/or content.

A dCDN implementation of CI/T MUST restrict the actions of a uCDN to the data corresponding to that uCDN. Failure to do so would allow uCDNs to detrimentally affect each other's efficiency by generating unnecessary acquisition or reacquisition load.

An origin that chooses to delegate its delivery to a CDN is trusting that CDN to deliver content on its behalf; the interconnection of CDNs is an extension of that trust to dCDNs. That trust relationship is a commercial arrangement, outside the scope of the CDNI protocols. So, while a malicious CDN could deliberately generate load on a dCDN using the CI/T interface, the protocol does not otherwise attempt to address malicious behavior between interconnected CDNs.

8.1. Authentication, Authorization, Confidentiality, Integrity Protection 🔐

A CI/T implementation MUST support Transport Layer Security (TLS) transport for HTTP (HTTPS) as per [RFC2818] and [RFC7230].

TLS MUST be used by the server side (dCDN) and the client side (uCDN) of the CI/T interface, including authentication of the remote end, unless alternate methods are used for ensuring the security of the information in the CI/T interface requests and responses (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).

The use of TLS for transport of the CI/T interface allows the dCDN and the uCDN to authenticate each other using TLS client authentication and TLS server authentication.

Once the dCDN and the uCDN have mutually authenticated each other, TLS allows:

• The dCDN and the uCDN to authorize each other (to ensure that they are receiving CI/T Commands from, or reporting status to, an authorized CDN).
• CDNI commands and responses to be transmitted with confidentiality.
• Protection of the integrity of CDNI commands and responses.

When TLS is used, the general TLS usage guidance in [RFC7525] MUST be followed.

The mechanisms for access control are dCDN-specific and are not standardized as part of this CI/T specification.

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 unauthorized users from generating unnecessary load in dCDNs or uCDNs due to revalidation, reacquisition, or unnecessary acquisition.

When deploying a network of interconnected CDNs, the possible inefficiencies related to the diamond configuration discussed in Section 2.2.1 should be considered.

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 interface. 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 the 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 by performing batch processing.

8.3. Privacy ✨

okay so bestie, the CI/T protocol does NOT carry any info about individual end users of a CDN 🙈 so there are no privacy concerns for end users. slay, we're safe on that front 🫶

BUT 😭 the CI/T protocol does carry stuff that CDN operators and content owners could consider commercially sensitive 💼 that's the tea. the good news is mutually authenticated TLS 🔐 (the setup we talked about in Section 8.1) keeps that data confidential while it's zipping around in transit 🦋 and it stops anyone who isn't the authorized dCDN from peeking at it 👀 literally main character energy for security 👑

the dCDN MUST ensure that it only exposes CI/T data related to a uCDN to clients it has authenticated as belonging to that uCDN. no sharing the tea with randos, periodt 💅

9. References 📚

9.1. Normative References 💖

• [RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation, selection, and registration of an Autonomous System (AS)", BCP 6, RFC 1930, DOI 10.17487/RFC1930, March 1996, <http://www.rfc-editor.org/info/rfc1930>.
• [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>.
• [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, DOI 10.17487/RFC2818, May 2000, <http://www.rfc-editor.org/info/rfc2818>.
• [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, <http://www.rfc-editor.org/info/rfc3986>.
• [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, DOI 10.17487/RFC5226, May 2008, <http://www.rfc-editor.org/info/rfc5226>.
• [RFC6707] Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content Distribution Network Interconnection (CDNI) Problem Statement", RFC 6707, DOI 10.17487/RFC6707, September 2012, <http://www.rfc-editor.org/info/rfc6707>.
• [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 2014, <http://www.rfc-editor.org/info/rfc7159>.
• [RFC7230] Fielding, R., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014, <http://www.rfc-editor.org/info/rfc7230>.
• [RFC7231] Fielding, R., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 10.17487/RFC7231, June 2014, <http://www.rfc-editor.org/info/rfc7231>.
• [RFC7232] Fielding, R., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests", RFC 7232, DOI 10.17487/RFC7232, June 2014, <http://www.rfc-editor.org/info/rfc7232>.
• [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, "Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 2015, <http://www.rfc-editor.org/info/rfc7525>.
• [RFC8006] Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma, "Content Delivery Network Interconnection (CDNI) Metadata", RFC 8006, DOI 10.17487/RFC8006, December 2016, <http://www.rfc-editor.org/info/rfc8006>.

9.2. Informative References 🌸

• [CBOR-CDDL] Vigano, C. and H. Birkholz, "CBOR data definition language (CDDL): a notational convention to express CBOR data structures", Work in Progress, draft-greevenbosch-appsawg-cbor-cddl-09, September 2016.
• [RFC7336] Peterson, L., Davie, B., and R. van Brandenburg, Ed., "Framework for Content Distribution Network Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336, August 2014, <http://www.rfc-editor.org/info/rfc7336>.
• [RFC7337] Leung, K., Ed., and Y. Lee, Ed., "Content Distribution Network Interconnection (CDNI) Requirements", RFC 7337, DOI 10.17487/RFC7337, August 2014, <http://www.rfc-editor.org/info/rfc7337>.
• [RFC7736] Ma, K., "Content Delivery Network Interconnection (CDNI) Media Type Registration", RFC 7736, DOI 10.17487/RFC7736, December 2015, <http://www.rfc-editor.org/info/rfc7736>.
• [RFC7975] Niven-Jenkins, B., Ed., and R. van Brandenburg, Ed., "Request Routing Redirection Interface for Content Delivery Network (CDN) Interconnection", RFC 7975, DOI 10.17487/RFC7975, October 2016, <http://www.rfc-editor.org/info/rfc7975>.

Appendix A. Formalization of the JSON Data 🧚

This appendix is non-normative. 🍓

The JSON data described in this document has been formalized using the CBOR Data Definition Language (CDDL) [CBOR-CDDL] (where "CBOR" means "Concise Binary Object Representation"), as follows: 💜

 CIT-object = CIT-command / Trigger-Status-Resource / Trigger-Collection

 CIT-command ; use media type application/cdni; ptype=ci-trigger-command
 = {
   ? trigger: Triggerspec
   ? cancel: [* URI]
   cdn-path: [* Cdn-PID]
 }

 Trigger-Status-Resource ; application/cdni; ptype=ci-trigger-status
 = {
   trigger: Triggerspec
   ctime: Absolute-Time
   mtime: Absolute-Time
   ? etime: Absolute-Time
   status: Trigger-Status
   ? errors: [* Error-Description]
 }

 Trigger-Collection ; application/cdni; ptype=ci-trigger-collection
 = {
   triggers: [* URI]
   ? staleresourcetime: int ; time in seconds
   ? coll-all: URI
   ? coll-pending: URI
   ? coll-active: URI
   ? coll-complete: URI
   ? coll-failed: URI
   ? cdn-id: Cdn-PID
 }

 Triggerspec = { ; see Section 5.2.1
   type: Trigger-Type
   ? metadata.urls: [* URI]
   ? content.urls: [* URI]
   ? content.ccid: [* Ccid]
   ? metadata.patterns: [* Pattern-Match]
   ? content.patterns: [* Pattern-Match]
 }
 Trigger-Type = "preposition" / "invalidate"
    / "purge" ; see Section 5.2.2

 Trigger-Status = "pending" / "active" / "complete" / "processed"
    / "failed" / "cancelling" / "cancelled" ; see Section 5.2.3

 Pattern-Match = { ; see Section 5.2.4
   pattern: tstr
   ? case-sensitive: bool
   ? match-query-string: bool
 }

 Absolute-Time = number ; seconds since UNIX epoch (Section 5.2.5)

 Error-Description = { ; see Section 5.2.6
   error: Error-Code
   ? metadata.urls: [* URI]
   ? content.urls: [* URI]
   ? metadata.patterns: [* Pattern-Match]
   ? content.patterns: [* Pattern-Match]
   ? description: tstr
 }

 Error-Code = "emeta" / "econtent" / "eperm" / "ereject"
    / "ecdn" / "ecanceled"  ; see Section 5.2.7

 Ccid = tstr ; see RFC 8006

 Cdn-PID = tstr .regexp "AS[0-9]+:[0-9]+"

 URI = tstr

---

Acknowledgments 💖

The authors thank Kevin Ma for his input, and Carsten Bormann for his review and formalization of the JSON data. 🫶

Authors' Addresses 🎀

Rob Murray Nokia 3 Ely Road Milton, Cambridge CB24 6DD United Kingdom

Email: rob.murray@nokia.com

Ben Niven-Jenkins Nokia 3 Ely Road Milton, Cambridge CB24 6DD United Kingdom

Email: ben.niven-jenkins@nokia.com