Internet DRAFT - draft-goldstein-cdni-metadata-model-extensions
draft-goldstein-cdni-metadata-model-extensions
Network Working Group G. Goldstein
Internet-Draft W. Power
Updates: 8006, 8008 (if approved) Lumen Technologies
Intended status: Standards Track G. Bichot
Expires: 8 September 2022 Broadpeak
A. Siloniz
Telefonica
7 March 2022
CDNI Metadata Model Extensions
draft-goldstein-cdni-metadata-model-extensions-02
Abstract
The Content Delivery Network Interconnection (CDNI) Metadata
interface enables interconnected Content Delivery Networks (CDNs) to
exchange content distribution metadata in order to enable content
acquisition and delivery. To facilitate a wider set of use cases
such as Open Caching, this document describes extensions to the CDNI
Metadata object model and its associated Capabilities model as
documented in "CDNI Metadata" RFC8006 and "CDNI Request Routing:
Footprint and Capabilities Semantics" RFC8008 .
This document is a reflection of the content in the Streaming Video
Alliance specification titled "SVA Configuration Interface: Part 2
Extensions to CDNI Metadata Object Model".
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 8 September 2022.
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Copyright Notice
Copyright (c) 2022 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 (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction and Scope . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 6
2. CDNI Metadata Model Extensions . . . . . . . . . . . . . . . 6
2.1. Cache Control Metadata . . . . . . . . . . . . . . . . . 8
2.1.1. MI.CachePolicy . . . . . . . . . . . . . . . . . . . 9
2.1.2. MI.NegativeCachePolicy . . . . . . . . . . . . . . . 11
2.1.3. MI.StaleContentCachePolicy . . . . . . . . . . . . . 12
2.1.4. MI.CacheBypassPolicy . . . . . . . . . . . . . . . . 14
2.1.5. MI.ComputedCacheKey . . . . . . . . . . . . . . . . . 16
2.2. Origin Access Metadata . . . . . . . . . . . . . . . . . 17
2.2.1. MI.SourceMetadataExtended . . . . . . . . . . . . . . 18
2.2.1.1. MI.SourceExtended . . . . . . . . . . . . . . . . 19
2.2.1.2. MI.LoadBalanceMetadata . . . . . . . . . . . . . 22
2.2.2. MI.Auth . . . . . . . . . . . . . . . . . . . . . . . 24
2.2.2.1. MI.HeaderAuth . . . . . . . . . . . . . . . . . . 24
2.2.2.2. MI.AWSv4Auth . . . . . . . . . . . . . . . . . . 26
2.3. Edge Control Metadata . . . . . . . . . . . . . . . . . . 28
2.3.1. MI.CrossOriginPolicy . . . . . . . . . . . . . . . . 28
2.3.1.1. MI.AccessControlAllowOrigin . . . . . . . . . . . 31
2.3.2. MI.AllowCompress . . . . . . . . . . . . . . . . . . 33
2.3.3. MI.TrafficType . . . . . . . . . . . . . . . . . . . 35
2.3.4. MI.OcnSelection . . . . . . . . . . . . . . . . . . . 36
2.3.4.1. MI.OcnDelivery . . . . . . . . . . . . . . . . . 37
2.4. Processing Stage Metadata . . . . . . . . . . . . . . . . 38
2.4.1. MI.ProcessingStages . . . . . . . . . . . . . . . . . 40
2.4.2. MI.StageRules . . . . . . . . . . . . . . . . . . . . 43
2.4.3. MI.ExpressionMatch . . . . . . . . . . . . . . . . . 45
2.4.4. MI.StageMetadata . . . . . . . . . . . . . . . . . . 46
2.4.5. MI.RequestTransform . . . . . . . . . . . . . . . . . 48
2.4.6. MI.ResponseTransform . . . . . . . . . . . . . . . . 49
2.4.7. MI.SyntheticResponse . . . . . . . . . . . . . . . . 50
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2.4.8. MI.HeaderTransform . . . . . . . . . . . . . . . . . 52
2.4.9. MI.HTTPHeader . . . . . . . . . . . . . . . . . . . . 54
2.5. General Metadata . . . . . . . . . . . . . . . . . . . . 55
2.5.1. MI.ServiceIDs . . . . . . . . . . . . . . . . . . . . 55
2.5.2. MI.PrivateFeatureList . . . . . . . . . . . . . . . . 57
2.5.2.1. MI.PrivateFeature . . . . . . . . . . . . . . . . 58
2.5.3. MI.RequestRouting . . . . . . . . . . . . . . . . . . 59
3. Metadata Expression Language . . . . . . . . . . . . . . . . 60
3.1. Expression Variables . . . . . . . . . . . . . . . . . . 62
3.2. Expression Operators and keywords . . . . . . . . . . . . 63
3.3. Expression Built-in Functions . . . . . . . . . . . . . . 64
3.3.1. Basic Functions: Type Conversions . . . . . . . . . . 64
3.3.2. Basic Functions: String Conversions . . . . . . . . . 65
3.3.3. Convenience Functions . . . . . . . . . . . . . . . . 65
3.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 66
3.4.1. Compile Time Errors . . . . . . . . . . . . . . . . . 66
3.4.2. Runtime Errors . . . . . . . . . . . . . . . . . . . 67
3.5. Expression Examples . . . . . . . . . . . . . . . . . . . 67
3.5.1. ComputedCacheKey . . . . . . . . . . . . . . . . . . 67
3.5.2. ExpressionMatch . . . . . . . . . . . . . . . . . . . 67
3.5.3. ResponseTransform . . . . . . . . . . . . . . . . . . 68
3.5.4. MI.ServiceIDs . . . . . . . . . . . . . . . . . . . . 68
4. CDNI Capabilities Extensions . . . . . . . . . . . . . . . . 69
4.1. FCI Metadata Object . . . . . . . . . . . . . . . . . . . 69
4.2. FCI Model Extensions . . . . . . . . . . . . . . . . . . 70
4.2.1. FCI.AuthTypes . . . . . . . . . . . . . . . . . . . . 70
4.2.2. FCI.ProcessingStages . . . . . . . . . . . . . . . . 72
4.2.3. FCI.SourceMetadataExtended . . . . . . . . . . . . . 73
4.2.4. FCI.RequestRouting . . . . . . . . . . . . . . . . . 74
4.2.5. FCI.PrivateFeatures . . . . . . . . . . . . . . . . . 75
4.2.5.1. FCI.PrivateFeature . . . . . . . . . . . . . . . 76
4.2.6. FCI.OcnSelection . . . . . . . . . . . . . . . . . . 76
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 77
5.1. CDNI Payload Types . . . . . . . . . . . . . . . . . . . 77
6. Security Considerations . . . . . . . . . . . . . . . . . . . 79
7. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 79
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 79
8.1. Normative References . . . . . . . . . . . . . . . . . . 79
8.2. Informative References . . . . . . . . . . . . . . . . . 80
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 81
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1. Introduction and Scope
The Content Delivery Network Interconnection (CDNI) Metadata
interface enables interconnected Content Delivery Networks (CDNs) to
exchange content distribution metadata in order to enable content
acquisition and delivery. To facilitate a wider set of use cases
encountered in the commercial CDN and Open Caching ecosystems, this
document describes extensions to the CDNI Metadata object model and
its associated Capabilities model.
The objectives of this document are:
1. Identify the requirements for extending [RFC8006] and [RFC8008]
and specify a set of extensions that realize these requirements.
2. Maintain backward compatibility with [RFC8006] and [RFC8008] by
not altering the definitions or semantics of the original object
model. All extensions are defined as new GenericMetadata
Objects.
3. Define the metadata object model independently of the APIs used
to publish and retrieve metadata.
Scope this document ADDRESSES:
1. Define and register CDNI GenericMetadata objects, as defined in
section 4 of [RFC8006].
2. Define and register CDNI Payload Types, as defined in section 7.1
of [RFC8006].
3. Define Capabilities Objects that facilitate advertisement of a
dCDN's support of these new metadata features, extending
definitions in section 5 of [RFC8008].
4. Specification of a Metadata Expression Language Section 3 used
within the metadata object model extensions.
5. Provide JSON examples illustrating real-world CDN and Open
Caching use cases.
Scope this document DOES NOT ADDRESS:
1. Metadata object model definitions already specified in [RFC8006].
2. Interface API definitions for publishing and retrieving
configuration metadata. The Metadata Interface (MI) as defined
in [RFC8006] can be used to retrieve metadata. To enable more
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sophisticated metadata configuration publishing workflows, the
Streaming Video Alliance (SVA) Open Caching API [OC-CI], as
documented in the SVA Configuration Interface Part 3 (Simple API)
and Part 4 (Advanced API) specifications can be used.
1.1. Terminology
For consistency with other CDNI documents this document follows the
CDNI convention of uCDN (upstream CDN) and dCDN (downstream CDN). It
should be noted, however, that uCDN and dCDN are roles that can be
played by a variety of entities in the distribution ecosystem. A
Content Provider, for example, can play the roles of a uCDN, while a
commercial CDN or Open Caching system can play either the roles of a
uCDN or dCDN. Additionally, this document reuses the terminology
defined in [RFC6707],[RFC7336], [RFC8006], [RFC8007] and [RFC8804].
The following terms are used throughout this document:
* API - Application Programming Interface
* AWS - Amazon Web Services
* CDN - Content Delivery Network
* CDNi - CDN Interconnect
* CORS - Cross-Origin Resource Sharing
* CP - Content Provider
* dCDN - Downstream CDN
* DNS - Domain Name System
* FCI - Footprint and Capabilities Advertising Interface
* HREF - Hypertext Reference (link)
* HTTP - Hypertext Transfer Protocol
* IETF - Internet Engineering Task Force
* ISP - Internet Service Provider
* JSON - JavaScript Object Notation
* MEL - Metadata Expression Language
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* Object - A collection of properties.
* OC - Open Caching
* OCN - Open Caching Node
* PatternMatch - An object which matches a string pattern
* UA - User Agent
* uCDN - Upstream CDN
* URI - Uniform Resource Identifier
* URN - Uniform Resource Name
* VOD - Video-on-Demand
* W3C - World Wide Web Consortium
1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. CDNI Metadata Model Extensions
This section details extensions to the CDNI Metadata model as defined
in Section 4 of [RFC8006], expressed as a set of new GenericMetadata
objects. To preserve backward compatibility with [RFC8006], no
changes are proposed to the original set of GenericMetadata.
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+---------+ +---------+ +------------+
|HostIndex++(*)+>+HostMatch++(1)+>+HostMetadata+------+(*)+-----+
+---------+ +---------+ +------+-----+ |
+ |
(*) +
+ V
+-> Contains or references V *****************
(1) One and only one +---------+ *GenericMetadata*
(*) Zero or more +--->+PathMatch| * Objects *<+
| +----+---++ ***************** |
+ + + ^ |
(*) (1) (1) +------------+ | |
+ + +->+PatternMatch| | |
| V +------------+ | |
| +------------+ | |
+--+PathMetadata+------+(*)+-----+ |
+------------+ |
|
|
|
+---------------------------------------+
|
+
New GenericMetadata Object by Categories (SVA)
+-------------------+ +-------------------+ +---------------------+
| Cache Control | | Origin Access | |Client Access Control|
+-------------------+ +-------------------+ +---------------------+
+-------------------+ +-------------------+ +---------------------+
| Edge Control | | Processing Stages | | General Metadata |
+-------------------+ +-------------------+ +---------------------+
Figure 1: CDNI Metadata Model with Extensions
The remainder of this section presents the extended set of
GenericMetadata objects organized by the categories in the above
diagram.
Note: In the following sections, the term "mandatory-to-specify" is
used to convey which properties MUST be included when serializing a
given capability object. When mandatory-to-specify is defined as
"Yes" for an individual property, it means that if the object
containing that property is included in a message, then the
mandatory-to-specify property MUST also be included.
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2.1. Cache Control Metadata
In addition to the cache control policies currently specified by CDNI
metadata, content providers often need more fine-grained control over
CDN caching, including scenarios where it is desirable to override or
adjust cache-control headers from the origin.
The following additional capabilities are needed for general CDN and
open caching use cases:
1. Positive Cache Control - Allows the uCDN to specify internal
caching policies for the dCDN and external caching policies
advertised to clients of the dCDN, overriding any cache control
policy set in the response from the uCDN.
2. Negative Cache Control - Allows the specification of caching
policies based on error response codes received from the origin,
allowing for fine-grained control of the downstream caching of
error responses. For example, it may be desirable to cache error
responses at the dCDN for a short period of time to prevent an
overwhelmed origin service or uCDN from being flooded with
requests.
3. Cache Bypass Control - Allows content providers to bypass CDN
caching when needed (typically for testing or performance
benchmarking purposes).
4. Stale Content Policies - Allows control over how the dCDN should
process requests for stale content. For example, this policy
allows the content provider to specify that stale content be
served from cache for a specified time period while refreshes
from the origin occur asynchronously.
5. Dynamically Constructed Cache Keys - While the properties
provided by the standard CDNI metadata Cache object provide some
simple control over the construction of the cache key, it is
typical in advanced CDN configurations to generate cache keys
that are dynamically constructed via lightweight processing of
various properties of the HTTP request and/or response. As an
example, an origin may specify a cache key as a value returned in
a specific HTTP response header. A rich expression language is
provided to allow for such advanced cache key construction.
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2.1.1. MI.CachePolicy
CachePolicy is a new GenericMetadata object that allows for the uCDN
to specify internal caching policies for the dCDN, as well as
external caching policies advertised to clients of the dCDN
(overriding any cache control policy set in the response from the
uCDN).
Property: internal
- Description: Specifies the internal cache control policy to be
used by the dCDN.
- Type: Number in seconds encoded as string (e.g. 5 is a five
second cache ) and/or a list of Enumeration [as-is|no-cache|no-
store]
- Mandatory-to-Specify: No. The default is to use the cache
control policy specified in the response from the uCDN.
Property: external
- Description: Specifies the external cache control policy to be
used by clients of this dCDN.
- Type: Number in seconds encoded as string (e.g. 5 is a five
second cache ) and/or a list of Enumeration [as-is|no-cache|no-
store]
- Mandatory-to-Specify: No. The default is to use the cache
control policy specified in the response from the uCDN.
Property: force
- Description: If set to True, the metadata interface cache
policy defined in the MI.CachePolicy will override any cache
control policy set in the response from the uCDN. If set to
False, the MI.CachePolicy is only used if there is no cache
control policy provided in the response from the uCDN.
- Type: Boolean
- Mandatory-to-Specify: No. The default is "False", which will
apply the MI.CachePolicy only if no policy is provided in the
response from the uCDN.
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Example 1: An MI.CachePolicy that sets the internal cache control
policy to five seconds. The external cache policy is set to 'no-
cache':
{
"generic-metadata-type": "MI.CachePolicy",
"generic-metadata-value": {
"internal": "5",
"external": "no-cache",
"force": "true"
}
}
Example 2: An MI.CachePolicy that sets the internal cache control
policy to "as-is" (keep the policy set in the response from the
uCDN). The external cache policy is set to 'no-cache:
{
"generic-metadata-type": "MI.CachePolicy",
"generic-metadata-value": {
"internal": "as-is",
"external": "no-cache",
"force": "true"
}
}
Example 3: An MI.CachePolicy in the context of the processing stages
model that sets a caching policy only if the HTTP status code
received from the origin is a 200. In this example, the internal
cache control policy is set to five seconds. The external cache
policy is set to 'no-cache'. Force is set to 'False', indicating
that the MI.CachePolicy only applies if there is no cache policy in
the response from the uCDN.
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{
"generic-metadata-type": "MI.ProcessingStages",
"generic-metadata-value": {
"origin-response": [
{
"match": {
"expression": "resp.status == 200"
},
"stage-metadata": {
"generic-metadata": [
{
"generic-metadata-type": "MI.CachePolicy",
"generic-metadata-value": {
"internal": "5",
"external": "no-cache",
"force": "false"
}
}
]
}
}
]
}
}
2.1.2. MI.NegativeCachePolicy
NegativeCachePolicy is a new GenericMetadata object that allows for
the specification of caching policies based on error response codes
received from the origin.
Property: error-codes
- Description: Array of HTTP response error status codes (See
Sections 6.5 and 6.6 of [RFC7231] , that if returned from the
uCDN, will be cached using the cache policy defined by the
cache-policy property.
- Type: Array of HTTP response error status codes
- Values: ["404", "503", "504"]
- Mandatory-to-Specify: No. The default is to revert to
[RFC8006] behavior.
Property: cache-policy
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- Description: MI.CachePolicy to apply to the HTTP response error
status codes returned by the uCDN.
- Mandatory-to-Specify: Yes
Example: A MI.NegativeCachePolicy that applies to HTTP error codes:
"404", "503", "504" and sets the internal cache control policy to
five seconds and external to 'no-cache'.
{
"generic-metadata-type": "MI.NegativeCachePolicy",
"generic-metadata-value": {
"error-codes": [ "404", "503", "504" ],
"cache-policy": {
"internal": "5",
"external": "no-cache",
"force": "true"
}
}
}
2.1.3. MI.StaleContentCachePolicy
MI.StaleContentCachePolicy is a new GenericMetadata object that
allows the uCDN to specify the policy to use by a dCDN when
responding with stale content. For example, this policy allows the
content provider to specify that stale content be served from cache
for a specified time period while refreshes from the origin occur
asynchronously.
Property: stale-while-revalidating
- Description: Instructs the dCDN to serve a stale version of a
resource while refreshing the resource with the uCDN. When set
to "True", the dCDN will return a previously cached version of
a resource while the resource is refreshed with the uCDN in the
background.
- Type: Boolean
- Mandatory-to-Specify: No. The default is False, which waits
for the uCDN to refresh a resource before responding to the
client.
Property: stale-if-error
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- Description: Instructs the dCDN to serve a stale version of a
resource if an error was received when trying to refresh the
resource with the uCDN. When set, the dCDN will return a
previously cached version of a resource instead of caching the
error response. Per Section 4 of [RFC5861], an error is any
situation that would result in a 500, 502, 503, or 504 HTTP
response status code being returned
- Type: Array of HTTP response error status codes. Example: [
"503", "504"]
- Mandatory-to-Specify: No. The default is to cache the error
response received from the uCDN.
Property: failed-refresh-ttl
- Description: Instructs the dCDN to serve a stale version of a
resource for the number of seconds specified in failed-refresh-
ttl before trying to revalidate the resource with the uCDN.
Use of failed-refresh-ttl allows the load to be reduced on the
uCDN during times of system stress.
- Type: Integer
- Mandatory-to-Specify: No
Example 1: A MI.StaleContentCachePolicy where stale-while-
revalidating is true, instructing the dCDN to respond with a stale
cached version of the resource while it refreshes the resource with
the uCDN in the background:
{
"generic-metadata-type": "MI.StaleContentCachePolicy",
"generic-metadata-value": {
"stale-while-revalidating": true
}
}
Example 2: A MI.StaleContentCachePolicy where stale-if-error
instructs the dCDN to use the stale cached resource if it receives an
error of type 503 or 504 when trying to refresh the resource with the
uCDN.
failed-refresh-ttl instructs the dCDN to use a five second cache TTL
on the resource that receives an error when refreshing from the uCDN.
That is, after five seconds, the dCDN will attempt to refresh the
resource with the uCDN.
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{
"generic-metadata-type": "MI.StaleContentCachePolicy",
"generic-metadata-value": {
"stale-if-error": [ "503", "504" ],
"failed-refresh-ttl": "5"
}
}
Example 3: A MI.StaleContentCachePolicy where stale-while-
revalidating is true, instructing the dCDN to respond with a stale
cached version of the resource while it refreshes the resource with
the uCDN in the background.
stale-if-error instructs the dCDN to use the stale cached resource if
it receives an error of type 404, 503, or 504 when trying to refresh
the resource with the uCDN.
failed-refresh-ttl instructs the dCDN to use a five second cache TTL
on the resource that receives an error when refreshing from the uCDN.
That is, after five seconds, the dCDN will attempt to refresh the
resource with the uCDN.
{
"generic-metadata-type": "MI.StaleContentCachePolicy",
"generic-metadata-value": {
"stale-while-revalidating": "true",
"stale-if-error": [ "404", "503", "504" ],
"failed-refresh-ttl": "5"
}
}
2.1.4. MI.CacheBypassPolicy
CacheBypassPolicy is a new GenericMetadata object that allows a
client request to be set as non-cacheable. It is expected that this
feature will be used to allow clients to bypass cache when testing
the uCDN fill path. Note: CacheBypassPolicy is typically used in
conjunction with a path match or match expression on a header value
or query parameter. Any content previously cached (by client
requests that do not set CacheBypassPolicy) is not evicted.
Property: bypass-cache
- Description: A Boolean value that can activate the feature for
a given client request. It is expected that this feature will
be used within ProcessingStages to allow a client request to be
marked to bypass cache.
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- Type: Boolean
- Mandatory-to-Specify: No. The default is False.
Example 1: A MI.CacheBypassPolicy with the client HTTP header of:
CDN-BYPASS: "True":
{
"generic-metadata-type": "MI.ProcessingStages",
"generic-metadata-value": {
"client-request": [
{
"match": {
"expression": "req.h.cdn-bypass == 'true'"
},
"stage-metadata": {
"generic-metadata": [
{
"generic-metadata-type": "MI.CacheBypassPolicy",
"generic-metadata-value": {
"bypass-cache": "true"
}
}
]
}
}
]
}
}
Example 2: A MI.CacheBypassPolicy that applies to all requests where
the host header is bypass.example.com:
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{
"generic-metadata-type": "MI.ProcessingStages",
"generic-metadata-value": {
"client-request": [
{
"match": {
"expression": "req.h.host == 'bypass.example.com'"
},
"stage-metadata": {
"generic-metadata": [
{
"generic-metadata-type": "MI.CacheBypassPolicy",
"generic-metadata-value": {
"bypass-cache": "true"
}
}
]
}
}
]
}
}
2.1.5. MI.ComputedCacheKey
While the properties provided by the standard CDNi metadata Cache
object (See Section 4.2.6 of [RFC8006]) provide some simple control
over the construction of the cache key, it is typical in advanced CDN
configurations to generate cache keys that are dynamically
constructed via lightweight processing of various properties of the
HTTP request and/or response. As an example, an origin may specify a
cache key as a value returned in a specific HTTP response header.
ComputedCacheKey is a new GenericMetadata object that allows for the
specification of a cache key using the metadata expression language.
Typical use cases would involve the construction of a cache key from
one or more elements of the HTTP request. In cases where both the
ComputedCacheKey and the Cache object are applied, the
ComputedCacheKey will take precedence.
Property: expression
- Description: The expression that specifies how the cache key
shall be constructed.
- Type: String. An expression using [CDNI-MEL] to dynamically
construct the cache key from elements of the HTTP request and/
or response.
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- Mandatory-to-Specify: Yes
Example, using a custom request header as the cache key instead of
the URI path:
{
"generic-metadata-type": "MI.ComputedCacheKey",
"generic-metadata-value": {
"expression": "req.h.X-Cache-Key"
}
}
2.2. Origin Access Metadata
The CDNI metadata definitions for sources (also known as origins in
the CDN industry), are extended to provide the following capabilities
required:
1. Designation as to whether a source requires HTTPS access.
2. Specification of the source's TCP port number.
3. Web root path specification for the source.
4. Indication as to whether redirects should be followed.
5. Support for additional forms of origin authentication.
6. Multi-origin failover - The ability to specify a list of origins
that can act as fallbacks to the primary origin. Failure rules
can specify types of errors and timeout values that trigger
failover.
7. Multi-origin load balancing - The ability to specify a list of
origins that can be selected by one of several balancing rules
(round robin, content hash, IP hash).
8. Specification of SNI configurations required for origin access.
9. Specification of connection control parameters for origin access.
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2.2.1. MI.SourceMetadataExtended
SourceMetadataExtended is an alternative to the CDNI standard
SourceMetadata object, which adds a property to specify load
balancing across multiple sources, as well as a SourceExtended sub-
object with additional attributes to the CDNI standard Source object.
While both SourceMetadataExtended and SourceMetadata can be provided
for backward compatibility, a dCDN that advertises capability for
SourceMetadataExtended will ignore SourceMetadata if both are
provided for a given host or path match.
Property: sources
- Description: Sources from which the dCDN can acquire content,
listed in order of preference.
- Type: Array of SourceExtended objects
- Mandatory-to-Specify: No. Default is to use static
configuration, out-of-band from the CDNI metadata interface.
Property: load-balance
- Description: Specifies load balancing rules for the set of
sources.
- Type: LoadBalanceMetadata object
- Mandatory-to-Specify: No
Example of a SourceMetadataExtended object with the associated
LoadBalanceMetadata configuration object:
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{
"generic-metadata-type": "MI.SourceMetadataExtended",
"generic-metadata-value": {
"sources": [
{
"endpoints": [
"a.service123.ucdn.example",
"b.service123.ucdn.example"
],
"protocol": "http/1.1"
},
{
"endpoints": [
"origin.service123.example"
],
"protocol": "http/1.1"
}
],
"load-balance": {
"balance-algorithm": "content-hash",
"balance-path-pattern": "^/prod/(.*)/.*\\.ts$"
}
}
}
2.2.1.1. MI.SourceExtended
SourceExtended is an alternative to the CDNI standard Source object
with additional metadata. It contains all the attributes of the
[RFC8006] Source object (acquisition-auth, endpoints, and protocol),
with additions specified below.
Property: acquisition-auth
- Description: Authentication method to use when requesting
content from this source. Same as [RFC8006].
- Type: Auth (see [RFC8006] Section 4.2.7 and the new MI.Auth
types in this specification)
- Mandatory-to-Specify: No. Default is no authentication
required.
Property: endpoints
- Description: Origins from which the dCDN can acquire content.
If multiple endpoints are specified, they are all equal, i.e.,
the list is not ordered by preference. Same as [RFC8006].
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- Type: Array of Endpoint objects (see [RFC8006] Section 4.3.3)
- Mandatory-to-Specify: Yes..
Property: protocol
- Description: Network retrieval protocol to use when requesting
content from this source. Same as [RFC8006].
- Type: Protocol (see [RFC8006] Section 4.3.2)
- Mandatory-to-Specify: Yes..
Property: origin-host
- Description: HTTP host header to pass to the endpoints when
retrieving content from a uCDN. The host MUST conform to the
Domain Name System (DNS) syntax defined in [RFC1034] and
[RFC1123]
- Type: String
- Mandatory-to-Specify: No. The default is to use the host name
passed by the dCDN.
Property: webroot
- Description: The path element that is prepended to a resource's
URI before retrieving content from a uCDN.
- Type: String
- Mandatory-to-Specify: No. The default is to use the original
URI.
Property: follow-redirects
- Description: If the follow-redirects property is set to "True",
HTTP redirect responses returned from a uCDN will be followed
when retrieving content. Otherwise, the HTTP redirect response
is returned to the client.
- Type: Boolean
- Mandatory-to-Specify: No. The default is "True" (i.e., follow
redirect responses from the uCDN).
Property: timeout-ms
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- Description: A timeout (in milliseconds) to apply when
connecting to a uCDN. If the connection is not established
within timeout-ms, this source is abandoned and the next source
in the MI.SourceMetadataExtended sources array is tried. Once
a connection is established, timeout-ms is used on subsequent
reads of data from the uCDN.
- Type: Integer
- Mandatory-to-Specify: No. The default is to revert to
[RFC8006] behavior.
Property: failover-errors
- Description: Array of HTTP response error status codes
(Section 6 of [RFC7231]), that if returned from the uCDN, will
trigger a failover to the next source in the
MI.SourceMetadataExtended sources array. If the uCDN returns
an HTTP error code that is not in the failover-errors array,
that error code is returned to the client of the dCDN.
- Type: Array of HTTP response error status codes.
- Mandatory-to-Specify: No. The default is to revert to
[RFC8006] behavior.
Example of a SourceExtended object that describes a pair of endpoints
(servers) that the dCDN can use to acquire content for the applicable
host and/or URI path:
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{
"generic-metadata-type": "MI.SourceMetadataExtended",
"generic-metadata-value": {
"sources": [
{
"endpoints": [
"a.service123.ucdn.example",
"b.service123.ucdn.example:8443"
],
"protocol": "https/1.1",
"origin-host": "internal.example.com",
"webroot": "/prod",
"follow-redirects": false,
"timeout-ms": 4000,
"failover-errors": [ "502", "503", "504" ]
},
{
"endpoints": [ "origin.service123.example" ],
"protocol": "http/1.1",
"webroot": "/prod",
"follow-redirects": true,
"timeout-ms": 8000
}
]
}
}
2.2.1.2. MI.LoadBalanceMetadata
The LoadBalanceMetadata object defines how content acquisition
requests are distributed over the SourceExtended objects listed in
the SourceMetadataExtended object.
Property: balance-algorithm
- Description: Specifies the algorithm to be used when
distributing content acquisition requests over the sources in a
SourceMetadataExtended object. The available algorithms are
random, content-hash, and ip-hash.
o random: Requests are distributed over the sources in proportion to
their associated weights.
o content-hash: Requests are distributed over the sources in a
consistent fashion, based on the balance-path-pattern property.
o ip-hash: Requests are distributed over the sources in a consistent
fashion based on the IP address of the client requestor.
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1. Type: Enumeration [random|content-hash|ip-hash] encoded as a
lowercase string.
2. Mandatory-to-Specify: No. The default is to use sources in
preference order as defined in the SourceMetadataExtended object.
Property: balance-weights
- Description: This property specifies the relative frequency
that a source is used when distributing requests. For example,
if there are three SourceExtended objects in a
SourceMetadataExtended object with balance-weights [1, 2, 1],
source 1 will receive 1/4 of the requests; source 2 will
receive 2/4 of the requests; source 3 will receive 1/4 of the
requests.
- Type: Array of integers
- Mandatory-to-Specify: No. The default is to use sources in
preference order as defined in the SourceMetadataExtended
object.
Property: balance-path-pattern
- Description: This property specifies a regular expression
pattern to apply to the URI when calculating the content hash
used by the balance-algorithm. For example, "balance-path-
pattern": "^/prod/(.*)/.*\.ts$" would distribute requests based
on the URI but excluding the /prod prefix and the .ts segment
file.
- Type: String (regular expression)
- Mandatory-to-Specify: No. The default is to use the original
URI.
Example 1: The LoadBalanceMetadata object distributes content
acquisition requests over sources using a content-hash algorithm:
{
"generic-metadata-type": "MI.LoadBalanceMetadata",
"generic-metadata-value": {
"balance-algorithm": "content-hash",
"balance-path-pattern": "^/prod/(.*)/.*\\.ts$"
}
}
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Example 2: The LoadBalanceMetadata object distributes content
acquisition requests over sources using the random algorithm:
{
"generic-metadata-type": "MI.LoadBalanceMetadata",
"generic-metadata-value": {
"balance-algorithm": "random",
"balance-weights": [ 1, 2, 1 ]
}
}
2.2.2. MI.Auth
To meet the typical industry requirements for authenticating CDNs to
external origins, two new authentication types are defined.
auth-type: MI.HeaderAuth
- Description: Header based authentication is used to pass an
HTTP header (secret-name) and value (secret-value) to a uCDN
when requesting content. The header name and value are agreed
upon between parties out of band.
- Note: We may want to add a way to encrypt or separately
communicate the secret; this could be a general capability for
CDNI.
- auth-value: MI.HeaderAuth object specifying the header name and
value (secret name, secret key) required for authenticated
access to an origin. For more information, refer to the
MI.HeaderAuth section below.
auth-type: MI.AWSv4Auth
- Description: Allows for the specification of a set of headers
to be added to requests that are forwarded to an origin to
enable Amazon Web Services (AWS) authentication, as documented
by AWS (See Specifications & Standards References).
- auth-value: MI.AWSv4Auth object specifying the access
parameters. For more information, refer to the MI.AWSv4Auth
section below.
2.2.2.1. MI.HeaderAuth
The HeaderAuth metadata object is used in the auth-value property of
the
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Auth object, as defined in [RFC8006] section 4.2.7, and may be
applied to any
source by including or referencing it under its authentication
property. This method of authentication provides a simple capability
for a mutually agreed upon header to be added by the CDN to all
requests sent to a specific origin. Note that if a dynamically
generated header value is required, the RequestTransform capabilities
within StageProcessing can be used.
Property: header-name
- Description: Name of the authentication header.
- Type: String
- Mandatory-to-Specify: Yes
Property: header-value
- Description: Value of the authentication header (typically a
pre-shared key). Note that this value SHOULD NOT be disclosed;
it SHOULD be protected by some mechanism such as a secret-
sharing API, which is outside the scope of this specification.
- Type: String
- Mandatory-to-Specify: Yes
Example Auth object for header authentication:
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{
"generic-metadata-type": "MI.SourceMetadataExtended",
"generic-metadata-value": {
"sources": [
{
"endpoints": [ "origin.example.com" ],
"protocol": "http/1.1",
"acquisition-auth": {
"generic-metadata-type": "MI.Auth",
"generic-metadata-value": {
"auth-type": "MI.HeaderAuth",
"auth-value": {
"header-name": "X-Origin-Auth",
"header-value": "SECRETKEYJKSDHFSIFUI4UFH78HW4NF7"
}
}
}
}
]
}
}
2.2.2.2. MI.AWSv4Auth
The AWSv4Auth metadata object is used in the auth-value property of
the Auth object as defined in [RFC8006] section 4.2.7, and may be
applied to any source by including or referencing it under its
authentication property.
AWSv4 authentication causes upstream requests to have a signature
applied, following the method described in [AWSv4Method]. A hash-
based signature is calculated over the request URI and specified
headers, and provided in an Authorization: header on the upstream
request. The signature is tied to a pre-shared secret key specific
to an AWS service, region, and key ID.
1. We may want to add a way to encrypt or separately communicate the
secret; this could be a general capability for CDNI.
2. We may want to add optional properties that allow overriding the
default headers to sign.
3. We may want to add optional properties that allow the signature
to be sent in a way other than with the Authorization: header
(e.g., query strings are also supported).
Property: access-key-id
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- Description: The preconfigured ID of the pre-shared
authorization secret.
- Type: String
- Mandatory-to-Specify: Yes
Property: secret-access-key
- Description: The pre-shared authorization secret, which is the
basis of building the signature. This is a secret key that
SHOULD NOT be disclosed; it SHOULD be protected by some
mechanism such as a secret-sharing API, which is outside the
scope of this specification.
- Type: String
- Mandatory-to-Specify: Yes
Property: aws-region
- Description: The AWS region name that is hosting the service
and shares the key ID and corresponding pre-shared secret.
- Type: String
- Mandatory-to-Specify: Yes
Property: aws-service
- Description: The AWS service name that is serving the upstream
requests.
- Type: String
- Mandatory-to-Specify: No. It defaults to "s3" if not
specified.
Property: host-name
- Description: The host name to use as part of the signature
calculation.
- Type: String
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- Mandatory-to-Specify: No. It defaults to using the value of
the Host: header of the upstream request. This property is
available in case the application needs to override that
behavior.
Example Auth object for AWSv4 authentication:
{
"generic-metadata-type": "MI.SourceMetadataExtended",
"generic-metadata-value": {
"sources": [
{
"endpoints": [ "origin.example.com" ],
"protocol": "http/1.1",
"acquisition-auth": {
"generic-metadata-type": "MI.Auth",
"generic-metadata-value": {
"auth-type": "MI.AWSv4Auth",
"auth-value": {
"access-key-id": "MYACCESSKEYID",
"secret-access-key": "SECRETKEYJKSDHFSIUHKWRGHHF",
"aws-region": "us-west-1"
}
}
}
}
]
}
}
2.3. Edge Control Metadata
CDNs typically require a set of configuration metadata to inform
processing of responses downstream (at the edge and in the user
agent). This section specifies GenericMetadata objects to meet those
requirements.
2.3.1. MI.CrossOriginPolicy
Delegation of traffic between a CDN over an open caching node based
on HTTP redirection does change the domain name in the client
requests. This represents a cross-origin request that must be
managed appropriately using Cross-Origin Resource Sharing (CORS)
headers in the responses.
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The dynamic generation of CORS headers is typical in modern HTTP
request processing and avoids CORS validation forwarded to the CDN
origin servers, particularly with the preflight OPTIONS requests.
The CDNI metadata model requires extensions to specify how a CDN or
open caching node should generate and evaluate these headers.
Required capabilities:
1. Set a default value for CORS response headers independent of the
origin request header value.
2. Match the origin request header with a list of valid values,
including PatternMatch, to return or not return the CORS response
headers.
3. Set a list of custom headers that can be exposed to the client
(expose headers).
4. Support for preflight requests using the OPTIONS method,
including custom header validation, expose headers, and methods.
5. Support for credentials validation within CORS.
Simple CORS requests are those where both HTTP method and headers in
the request are included in the safe list defined by the World Wide
Web Consortium [W3C]. The user agent (UA) request can include an
origin header set to the URL domain of the webpage that the player
runs. Depending on the metadata configuration, the logic to apply by
the open caching node (OCN) is:
1. Validation of the origin header - Metadata can include a list of
valid domains to validate the request origin header. If it does
not match, the CORS header must not be included in the response.
2. WIldcard usage - Depending on the configuration, the resultant
CORS header to include in the response will be the same as the
request origin header, or a wildcard.
3. If no validation of request is included in the origin header, set
a default value for CORS response headers independent of the
origin request header value.
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When a UA makes a request that includes a method or headers that are
not included in the safe-list, the client will make a CORS preflight
request using the OPTIONS method to the resource including the origin
header. If CORS is enabled and the requests passes the origin
validation, the OCN SHOULD respond with the set of headers that
indicate what is permitted for that resource, including one or more
of the following:
1. Allowed methods
2. Allowed credentials
3. Allowed request headers
4. Max age that the OPTIONS request is valid
5. Headers that can be exposed to the client
CrossoriginPolicy is a GenericMetadata object that allows for the
specification of dynamically generated CORS headers.
Property: allow-origin
- Description: Validation of simple CORS requests.
- Type: Object MI.AccessControlAllowOrigin
- Values: One element for each of the following properties.
- Mandatory-to-Specify: Yes
Property: expose-headers
- Description: A list of values the OCN will include in the
Access-Control-Expose-Headers response header to a preflight
request.
- Type: Array of strings
- Mandatory-to-Specify: No
Property: allow-methods
- Description: A list of values the OCN will include in the
Access-Control-Allow-Methods response header to a preflight
request.
- Type: Array of strings
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- Mandatory-to-Specify: No
Property: allow-headers
- Description: A list of values the OCN will include in the
Access-Control-Allow-Headers response header to a preflight
request.
- Type: Array of strings
- Mandatory-to-Specify: No
Property: allow-credentials
- Description: The value the OCN will include in the Access-
Control-Allow-Credentials response header to a preflight
request.
- Type: Boolean
- Mandatory-to-Specify: No
Property: max-age
- Description: The value the OCN will include in the Access-
Control-Max-Age response header to a preflight request.
- Type: Integer
- Mandatory-to-Specify: No
2.3.1.1. MI.AccessControlAllowOrigin
The MI.AccessControlAllowOrigin object has the following properties:
Property: allow-list
- Description: List of valid URLs that will be used to match the
request origin header. The Origin header is a HTTP extension.
Its value is a version of the Referer header in some specific
requests, and used for Cross Origin requests. . Permitted
values are schema://hostname[:port]
- Type: Array of PatternMatch objects
- Mandatory-to-Specify: Yes
Property: wildcard-return
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- Description: If "True", the OCN will include a wildcard (*) in
the Access-Control-Allow-Origin response header. If "False",
the OCN will reflect the request origin header in the Access-
Control-Allow-Origin response header.
- Type: Boolean
- Mandatory-to-Specify: Yes
The examples below demonstrate how to configure response headers
dynamically for CORS validation.
Example 1: A simple CORS validation configuration:
{
"generic-metadata-type": "MI.CrossoriginPolicy",
"generic-metadata-value": {
"allow-origin": {
"allow-list": [
{
"pattern": "*"
}
],
"wildcard-return": true
}
}
}
Example 2: Validation of a preflight request when some of the headers
included in the subsequent object request are not included in the
CORS specification safelist:
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{
"generic-metadata-type": "MI.CrossoriginPolicy",
"generic-metadata-value": {
"allow-origin": {
"allow-list": [
{
"pattern": "*://sourcepage.example.com"
},
"wildcard-return": false
},
"allow-methods": [ "GET", "POST" ],
"allow-credentials": true,
"allow-headers": [ "X-PINGOTHER", "Content-Type" ],
"expose-headers": [ "X-User", "Authorization" ],
"max-age": 3600
}
}
}
2.3.2. MI.AllowCompress
Downstream CDNs often have the ability to compress HTTP response
bodies in cases where the client has declared that it can accept
compressed responses (via an Accept-Encoding header), but the source/
origin has returned an uncompressed response.
The specific compression algorithm used by the dCDN is negotiated by
the client's Accept-Encoding header according to [RFC7694] (including
q= preferences) and the compression capabilities available on the
dCDN.
In addition, HeaderTransform allows the uCDN to normalize, or modify,
the Accept-Encoding header to allow for fine-grain control over the
selection of the compression algorithm (e.g., gzip, compress,
deflate, br, etc.).
AllowCompress is a new GenericMetadata object that allows the dCDN to
compress content before sending to the client.
Property: allow-compress
- Description: If set to "True", then the dCDN will try to
compress the response to the client based on the Accept-
Encoding request header.
- Type: Boolean
- Values: True or False
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- Mandatory-to-Specify: No. The default is "False".
Example 1: An MI.AllowCompress that allows manifests (*.m3u8) to be
compressed by the dCDN:
{
"match": {
"expression": "req.h.uri *= '*.m3u8'"
},
"stage-metadata": {
"generic-metadata": [
{
"generic-metadata-type": "MI.AllowCompress",
"generic-metadata-value": {
"allow-compress": "true"
}
}
]
}
}
Example 2: An MI.AllowCompress that allows manifests (*.m3u8) to be
compressed by the dCDN but normalizing the client's Accept-Encoding
header:
{
"match": {
"expression": "req.h.accept-encoding *= '*gzip*'"
},
"stage-metadata": {
"generic-metadata": [
{
"generic-metadata-type": "MI.AllowCompress",
"generic-metadata-value": {
"allow-compress": "true"
}
}
]
}
}
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2.3.3. MI.TrafficType
Content delivery networks often apply different infrastructure,
network routes, and internal metadata for different types of traffic.
Delivery of large static objects (such as software downloads), may,
for example, use different network routes than video stream delivery.
In an HTTP adaptive bitrate video service, every video title
corresponds to a set of video files and descriptors according to
different video protocols, and this is independent of the type of
service (Video-on-Demand, Live, Catch-up, etc.).
The way the video service is consumed by the user agents can vary.
For instance, a segment that belongs to a Video-on-Demand (VoD) title
can be requested for every moment the content is available for the
user agents to consume, while a segment of live content will be only
requested as long as the time-shift duration is configured for that
service. Knowing those differences, a CDN or OCN provider can
implement specific strategies that will maximize performance and
thereby provide more available capacity to the upstream provider. It
should be noted that the dCDNs handling of the traffic types is
implementation-specific and not prescribed here.
TrafficType metadata defines a set of descriptors that characterize
either the type or usage of the traffic, enabling CDNs and OCNs to
apply any internal configuration rules without exposing an
unnecessary number of internal details. Note that the interpretation
of these traffic types and application of rules such as rate limiting
or delivery pacing are implementation specific.
Property: traffic-type
- Description: A literal that defines the traffic type. uCDN will
use the literal that is most representative of the traffic
being delegated.
- Type: Enumeration [vod, live, object-download] encoded as
lowercase string
- Mandatory-to-Specify: Yes
Property: hints
- Description: Other traffic characteristics that the uCDN can
indicate to the dCDN as suggestions for service optimization.
Accepts free-form unconstrained values.
- Type: Array of strings
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- Mandatory-to-Specify: No
A TrafficType definition example for HostMetadata:
{
"generic-metadata-type": "MI.TrafficType",
"generic-metadata-value": {
"traffic-type": "vod",
"hints": [ "low-latency", "catch-up" ]
}
}
2.3.4. MI.OcnSelection
Configuration metadata is required to permit several levels of OCN
selection policies. For example, in a mobile network, several
physical locations are possible (i.e., candidates) for hosting the
OCN that will take charge in the delegation for the uCDN. This is
the case when the cache is virtualized and deployed dynamically.
Depending on the OCN selection policy (which may be a cost driver),
the dCDN may attempt to favor certain types of caches at the edge,
for example. The default OCN selection policy might be "best-
effort". Another one might be linked to the network characteristics
like "Edge" or ("average latency< 10ms").
OcnSelection is a new GenericMetadata object that allows the uCDN to
indicate to the dCDN a preference in terms of OCN selection.
Property: ocn-delivery
- Description: Instructs the dCDN to perform delegation operating
a particular medium and/or a transport arrangement.
- Type: Object MI.OcnDelivery
- Mandatory-to-Specify: No. At least one of the two properties,
ocn-type or ocn-delivery, must be present.
Property: ocn-type
- Description: Instructs the dCDN to perform delegation operating
the type of open caching nodes.
- Type: A string corresponding to one of the open caching node
types announced by the dCDN through the FCI interface.
- Mandatory-to-Specify: No. At least one of the two properties,
ocn-type or ocn-delivery, must be present.
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Property: ocn-selection
- Description: This property enforces the selection of OCNs,
considering the ocn-type and/or the ocn-delivery properties.
"False" means best-effort.
- Type: string. "attempt-or-failed" and "attempt-or-besteffort"
mean that the delegation must be attempted considering the ocn-
type and/or the ocn-delivery properties. If not possible, it
is considered as an error and either fails (configuration
failure) or the dCDN continues with a best-effort procedure.
Last, "best effort" means the dCDN tries its best to fulfil the
requested ocn-selection policy.
- Mandatory-to-Specify: No. Best-effort is the default OCN
selection policy.
2.3.4.1. MI.OcnDelivery
An ocn-delivery object contains the following properties:
Property: ocn-medium
- Description: Instructs the dCDN to perform delegation operating
a particular medium. The following values are specified:
"SATELLITE".
- Type: String
- Mandatory-to-Specify: No. Either the ocn-medium property or
the ocn-transport property must be present.
Property: ocn-transport
- Description: Instructs the dCDN to perform delegation operating
a particular transport arrangement. The following values are
specified: "MABR".
- Type: String
- Mandatory-to-Specify: No. At least one of the two properties
(ocn-medium or ocn-transport) must be present.
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2.4. Processing Stage Metadata
It is typical in CDN configurations to define matching rules and
metadata that are to be applied at specific stages in the request
processing pipeline. For example, it may be required to append a
host header prior to forwarding a request to an origin, or modify the
response returned from an origin prior to storing in the cache.
+-------+ +---------------+ +--------+
| +--->|A B+--->| |
| | | | | uCDN |
| UA | | dCDN | | |
| | | | | Source |
| |<---+D C|<---+ |
+-------+ +---------------+ +--------+
Figure 2: Processing stages
Processing stages:
1. clientRequest - Rules run on the client request prior to further
processing.
2. originRequest - Rules run prior to making a request to the
origin.
3. originResponse - Rules run after a response is received from the
origin and before being placed in the cache.
4. clientResponse - Rules run prior to sending the response to the
client. If the response is from the cache, rules are applied to
the response retrieved from the cache prior to sending to the
client.
Requirements:
1. Header Matching - While CDNI metadata defines some basic
matching rules for host names and pattern patching on paths, CDN
and open caching use cases often require matching on specific
fields in Hypertext Transfer Protocol (HTTP) request and
response headers to set metadata. A typical example may be
matching on a user agent string to set access controls or
matching on a mime-type header to set caching rules. A rich
expression matching syntax that allows matching on any
combination of host, path, and header values covers most typical
use cases.
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2. Expression Matching - Header matching alone is not always
sufficient for identifying a set of requests or responses that
require specific metadata. CDN and open caching systems often
require a rich set of matching rules, with full regular
expressions and Boolean combinations of matching parameters for
host, path, and header elements of a request. In typical CDN
implementations, this capability is provided by a rich
expression language that can be embedded in the metadata
configurations.
3. URI Modifications - In processing HTTP requests, modifications
to the request Uniform Resource Identifier (URI) are often
required for uses such as collapsing multiple paths to a common
cache key or normalizing file extension naming conventions
before making a request to the origin. In cases where the
modified URI needs to be constructed dynamically, an expression
language is provided that allows elements of requests and
responses to be concatenated with string literals.
4. Header Modifications - In processing HTTP requests, it is often
required to modify HTTP request or response headers at one of
the processing stages, requiring CDNI metadata to have the
capability to update any field in an HTTP request or response
header. It should be noted that certain HTTP headers (such as
Set-Cookie) have multiple occurrences in a request or response,
thereby requiring that we allow for add and replace designations
for header modification. In cases where a header value needs to
be constructed dynamically, an expression language is provided
that allows elements of requests and responses to be
concatenated with string literals. All of the following
capabilities are required at each processing stage:
5. Add Request Header Field - Add a header name/value to the
request, along with any headers of the same name that may
already be present.
6. Replace Request Header Field - Add a header name/value to the
request, replacing any headers of the same name that may already
be present.
7. Delete Request Header Field - Delete all occurrences of the
named header from the request.
8. Add Response Header Field - Add a header name/value to the
response, along with any headers of the same name that may
already be present.
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9. Replace Response Header Field - Add a header name/value to the
response, replacing any headers of the same name that may
already be present.
10. Delete Response Header Field - Delete all occurrences of the
named header from the response.
11. Synthetic Responses - It is quite common in CDN configurations
to specify a synthetic response be generated based on inspection
of aspects of the original request or the origin response. The
synthetic response capability allows for the specification of a
set of response headers, a status code, and a response body. In
cases where a header value or the synthetic response body needs
to be constructed dynamically, an expression language is
provided that allows elements of requests and responses to be
concatenated with string literals.
2.4.1. MI.ProcessingStages
A ProcessingStages object is a new GenericMetadata which describes
the matching rules, metadata, and transformations to be applied at
specific stages in the request processing pipeline. The processing
rules and transformations are defined as a child data model
referenced within a ProcessingStages object, as defined below.
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+----------------+
|ProcessingStages|
+----------------+
(*)
|
+----------------+-------+---------+----------------+
| | | |
v v v v
+-------------+ +-------------+ +--------------+ +--------------+
|ClientRequest| |OriginRequest| |OriginResponse| |ClientResponse|
+-------------+ +-------------+ +--------------+ +--------------+
(*) (*) (*) (*)
| | | |
+---------------+----------------+----------------+
|
| +---------------+
| +-------->|ExpressionMatch|
| | +---------------+
| |
| | *****************
| (*) +--->*GenericMetadata*
| +----------+ +-------------+ | * Objects *
+--->+StageRules+--->|StageMetadata+(*)-+ *****************
+----------+ +-------------+
(*) (*)
| |
+-------+ +-----------+
| |
v v
+----------------+ +-----------------+
|RequestTransform|(*)-+ +-(*)|ResponseTransform|
+----------------+ | | +-----------------+
(*) | |
| | |
| v v
| +---------------+
| |HeaderTransform|(*)-+
| +---------------+ |
| |
v |
+-----------------+ |
|SyntheticResponse|(*)--+ v
+-----------------+ | +----------+
+----->|HTTPHeader|
+----------+
Figure 3: CDNi ProcessingStages metadata model with contained objects
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Each of the four processing stages is represented by an array of
StageRules objects, with each StageRules object defining criteria
along with metadata that MUST be applied if the match applies to
"True". It should be noted that the StageRules objects in the array
are evaluated and processed in order. A possible future extension to
this processing model could allow for an if-else structure, where
processing for a stage is halted upon the first match of a StageRules
expression.
Property: client-request
- Description: Allows for the specification of conditional
metadata to be applied at the client request processing stages,
as defined in the Rule Processing Stages section. The
StageRules in the array are evaluated in order.
- Type: Array of StageRules objects
- Mandatory-to-Specify: No
Property: origin-request
- Description: Allows for the specification of conditional
metadata to be applied at origin request processing stages, as
defined in the Rule Processing Stages section. The StageRules
in the array are evaluated in order.
- Type: Array of StageRules objects
- Mandatory-to-Specify: No
Property: origin-response
- Description: Allows for the specification of conditional
metadata to be applied at origin response processing stages, as
defined in the Rule Processing Stages section. The StageRules
in the array are evaluated in order.
- Type: Array of StageRules objects
- Mandatory-to-Specify: No
Property: client-response
- Description: Allows for the specification of conditional
metadata to be applied at client response processing stages, as
defined in the Rule Processing Stages section. The StageRules
in the array are evaluated in order.
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- Type: Array of StageRules objects
- Mandatory-to-Specify: No
Example specifying all four processing stages. In this example, the
client-request stage has two StageRules, appling one set of metadata
if "ExpressionMatch1" evaluates to "True" and applying another set of
metadata if "ExpressionMatch2" evaluates to "True".
{
"generic-metadata-type": "MI.ProcessingStages",
"generic-metadata-value": {
"client-request" : [
{
"match" : < ExpressionMatch1 for conditional metadata >
"stage-metadata" : <StageMetadata1 for clientRequest stage>,
},
{
"match" : <Additional ExpressionMatch2 for conditional metadata >
"stage-metadata" : <StageMetadata2 for clientRequest stage>,
}
],
"origin-request" : [{
"match" : <Optional ExpressionMatch for conditional metadata >
"stage-metadata" : <StageMetadata for originRequest stage>,
}],
"origin-response" : [{
"match" : <Optional ExpressionMatch for conditional metadata >
"stage-metadata" : <StageMetadata for originResponse stage>,
}],
"client-response" : [{
"match" : <Optional ExpressionMatch for conditional metadata >
"stage-metadata" : <StageMetadata for clientResponse stage>,
}]
}
}
2.4.2. MI.StageRules
A StageRules object is used within the context of ProcessingStages to
define elements in a list of match rules and stage-specific metadata
and transformations that MUST be applied conditionally on a rich
expression match.
Property: match
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- Description: An ExpressionMatch object encapsulating a rich
expression using the CDNI Metadata Expression Language [CDNI-
MEL] to evaluate aspects of the HTTP request and/or response.
The stage-metadata rules are only applied if the match
evaluates to "True" or if no match expression is provided
- Type: ExpressionMatch object
- Mandatory-to-Specify: No. The stage-metadata rules are always
applied if no match expression is provided. This would be the
case when stage-metadata should be applied unconditionally
within the context of the higher-level host and path matches.
Property: stage-metadata
- Description: Specifies the set of StageMetadata to be applied
at the processing stage if the match expression evaluates to
"True" or is not present.
- Type: Array of StageMetadata objects, applied in order.
- Mandatory-to-Specify: Yes
An example of StageRules that are applied just after responses are
received from the origin. In this example, receipt of a response
status code of 304 from the origin indicates that CachePolicy
metadata SHOULD be applied (as specified via an external HREF), and
that response headers SHOULD be modified (X-custom-response-header
added and ETag deleted).
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{
"match": {
"expression": "resp.status == 304"
},
"stage-metadata": {
"generic-metadata": [
{
"type": "MI.CachePolicy",
"href": "https://metadata.ucdn.example/origin_response_cache"
}
],
"response-transform": {
"headers": {
"add": [
{
"name": "X-custom-response-header",
"value": "header-value"
}
],
"delete": [ "ETag" ]
}
}
}
}
2.4.3. MI.ExpressionMatch
The ExpressionMatch object contains the rich expression that must
evaluate to "True" for the StageMetadata to be applied for the
specific StageRules. Defining expressions as stand-alone objects
allows for sets of reusable match expressions to be reused via
metadata reference linking.
Property: expression
- Description: A rich expression using CDNI-MEL to evaluate
aspects of the HTTP request and/or response. See documentation
on the Metadata Expression Language for details on the
expression of matching variables and syntax.
- Type: String, using CDNI-MEL syntax. See the METADATA
EXPRESSION LANGUAGE (CDNI-MEL) section.
- Mandatory-to-Specify: Yes
Example of ExpressionMatch on the referrer and user agent request
headers:
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{
"expression" : "req.h.user-agent *= '*Safari*' and req.h.referrer == 'www.myhost.com'"
}
2.4.4. MI.StageMetadata
The StageMetadata object contains GenericMetadata and HTTP request/
response transformations that MUST be applied for a StageRules match.
The following table defines the processing stages where request and
response transformations are possible:
+================+===================+====================+
| Stage | request-transform | response-transform |
+================+===================+====================+
| clientRequest | yes | yes |
+----------------+-------------------+--------------------+
| originRequest | yes | yes |
+----------------+-------------------+--------------------+
| originResponse | no | yes |
+----------------+-------------------+--------------------+
| clientResponse | no | yes |
+----------------+-------------------+--------------------+
Table 1: StageMetadata stages
Note that for the stages where both request and response
transformations are allowed, it is possible to specify both. This
may be the case if, for example, the request URI needs alteration for
cache-key generation and the response headers need to be manipulated.
Property: generic-metadata
- Description: Specifies the set of GenericMetadata to be applied
for a StageRules match. A typical use case would be the
application of a CachePolicy or TimeWindowACL conditionally on
matching HTTP headers. Support for this capability is optional
and can be advertised via feature-flags in the FCI interface.
- Type: Array of GenericMetadata, applied in order. Note that
not all GenericMetadata object types may be applicable at all
processing stages.
- Mandatory-to-Specify: No. The generic-metadata property would
not be needed when StageMetadata is used to only specify
request or response transformations, such as modifications of
HTTP headers.
Property: request-transform
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- Description: Specifies a transformation to be applied to the
HTTP request for a StageRules match. The transformation can be
the modification of any request header and/or the modification
of the URI. Modifications are applied such that downstream
processing stages receive the modified HTTP request as their
input. Support for this capability is optional and can be
advertised via feature-flags in the FCI interface.
- Type: RequestTransform object
- Mandatory-to-Specify: No
Property: response-transform
- Description: Specifies a transformation to be applied to the
HTTP response for a StageRules match. The transformation can
be the modification of any response header, HTTP response
status code, or the generation of a synthetic response.
Modifications are applied such that downstream processing
stages receive the modified HTTP response as their input.
Support for this capability is optional and can be advertised
via feature-flags in the FCI interface.
- Type: ResponseTransform object
- Mandatory-to-Specify: No
Example of a StageMetadata object:
{
"generic-metadata" : [{
< Optional list of generic metadata to apply at this stage >
}],
"request-transform" : {
"headers" : { <list of request headers to add/replace/delete> },
"uri" : < URI rewrite, either static or dynamically constructed>
}
"response-transform" : {
"headers" : { <list of response headers to add/replace/delete> },
"response-status" : <Status either static or dynamically constructed >
}
}
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2.4.5. MI.RequestTransform
The RequestTransform object contains metadata for transforming the
HTTP request for a specific StageRules object. The transformation
can be the modification of any request header and/or the modification
of the URI. Modifications are applied such that downstream
processing stages receive the modified HTTP request as their input.
Property: headers
- Description: A HeaderTransform object specifying HTTP request
headers to add, replace, or delete.
- Type: HeaderTransform object
- Mandatory-to-Specify: No
Property: uri
- Description: Replacement value for the HTTP request.
- Type: String. Either a literal (static string) or an
expression using CDNI-MEL to dynamically construct a URI value
from elements of the HTTP request and/or response.
- Mandatory-to-Specify: No
Property: uri-is-expression
- Description: Flag to signal whether the URI is a static string
literal or a CDNI-MEL expression that needs to be dynamically
evaluated.
- Type: Boolean
- Mandatory-to-Specify: No. The default is "False", indicating
that the URI is a string literal and does not need to be
evaluated.
Example of a RequestTransform object illustrating a dynamically
constructed URI rewrite:
{
"request-transform" : {
"headers" : { <Optional list of request headers to add/replace/delete> },
"uri" : "req.uri.path",
"uri-is-expression" : true
}
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2.4.6. MI.ResponseTransform
The ResponseTransform object contains metadata for transforming the
HTTP response for a StageRules match. The transformation can be the
modification of any response header, HTTP response status code, or
the generation of a synthetic response. Modifications are applied
such that downstream processing stages receive the modified HTTP
response as their input.
Property: headers
- Description: A HeaderTransform object specifying HTTP response
headers to add, replace, or delete.
- Type: HeaderTransform object
- Mandatory-to-Specify: No
Property: response-status
- Description: Replacement value for the HTTP response status
code.
- Type: Integer. Either a static integer or an expression using
CDNI-MEL that evaluates to an integer to dynamically generate
an HTTP status code based on elements of the HTTP request and/
or response. Expressions that do not evaluate to an integer
shall be considered invalid and result in no override of
origin-provided response status.
- Mandatory-to-Specify: No
Property: status-is-expression
- Description: Flag to signal whether the response-status is a
static integer or a CDNI-MEL expression that needs to be
dynamically evaluated to generate an HTTP response status code.
- Type: Boolean
- Mandatory-to-Specify: No. The default is "False", indicating
that the response-status is a static integer and does not need
to be evaluated.
Property: synthetic
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- Description: Specification of a complete replacement of any
HTTP response that may have been generated in an earlier
processing stage with a synthetic response. Use of this
property to specify a synthetic response would override any
response transformations or status codes specified by other
properties.
- Type: SyntheticResponse object
- Mandatory-to-Specify: No
Example of a ResponseTransform object, illustrating a dynamically
constructed header value that uses the expression language to
concatenate the user agent and host header, and forces a 403 HTTP
response status code:
{
"response-transform": {
"headers": {
"add": [
{
"name": "X-custom-response-header",
"value": "req.h.user-agent . ‘-‘ . req.h.host",
"value-is-expressions": true
}
]
},
"response-status": "403"
}
}
2.4.7. MI.SyntheticResponse
The SyntheticResponse object allows for the specification of a
synthetic response to be generated in response to the HTTP request
being processed. The synthetic response can contain a set of
response headers, a status code, and a response body, and is a
complete replacement for any HTTP response elements generated in an
earlier processing stage.
A dynamically generated Content-Length HTTP response header is
generated based on the length of the generated response body.
Property: headers
- Description: An array of HTTP header objects that specify the
full set of headers to be applied to the synthetic response.
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- Type: Array of HTTP header objects
- Mandatory-to-Specify: No, although it would be unusual to not
specify minimal standard response headers, such as Content-
Type.
Property: response-status
- Description: HTTP response status code.
- Type: Integer. Either a static integer or an expression using
CDNI-MEL that evaluates to an integer to dynamically generate
an HTTP status code based on elements of the upstream HTTP
request and/or response. Expressions that do not evaluate to
an integer shall be considered invalid and result in a 500
status for the synthetic response.
- Mandatory-to-Specify: Yes
Property: status-is-expression
- Description: Flag to signal whether the response-status is a
static integer or a CDNI-MEL expression that needs to be
dynamically evaluated to generate an HTTP response status code.
- Type: Boolean
- Mandatory-to-Specify: No. The default is "False", indicating
that the response-status is a static integer and does not need
to be evaluated.
Property: body
- Description: Body for the synthetic HTTP response. The
response body can either be static or dynamically constructed
from a rich expression.
- Type: String. Either a literal (static string) or an
expression using CDNI-MEL to dynamically construct a response
body from elements of the HTTP request and/or response.
- Mandatory-to-Specify: No. If absent, an empty HTTP response
with a zero-value Content-Length header is generated.
Property: body-is-expression
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- Description: Flag to signal whether the synthetic response body
is a static string literal or a CDNI-MEL expression that needs
to be dynamically evaluated.
- Type: Boolean
- Mandatory-to-Specify: No. The default is "False", indicating
that the body is a string literal and does not need to be
evaluated.
Example of a SyntheticResponse object illustrating a dynamically
constructed response body that uses the expression language to
combine the request URI with static text and forces a 405 HTTP
response status code:
{
"headers": [
{
"name": "content-type",
"value": "text/plain"
},
{
"name": "X-custom-response-header",
"value": "some static value"
}
],
"response-status": "405",
"response-body": "'Sorry, Access to resource '.req.uri.' not allowed'",
"body-is-expression": false
}
2.4.8. MI.HeaderTransform
The HeaderTransform object specifies how HTTP headers MUST be added,
replaced, or deleted from HTTP requests and responses.
Property: add
- Description: List of HTTP headers (name/value pairs) that MUST
be added to the HTTP request or response. Note that any
existing headers in the request or response with the same names
of those added are not affected, resulting in multiple headers
with the same name.
- Type: Array of HTTPHeader objects containing header name/value
pairs
- Mandatory-to-Specify: No
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Property: replace
- Description: List of HTTP headers (name/value pairs) that MUST
be added to the HTTP request or response, replacing any
previous headers with the same name.
- Type: Array of HTTPHeader objects containing header name/value
pairs
- Mandatory-to-Specify: No
Property: delete
- Description: List of names of HTTP headers that MUST be deleted
from the
- HTTP request or response. If a named header appears multiple
times, all occurrences are deleted.
- Type: Array of strings, with each string naming an HTTP header
to delete
- Mandatory-to-Specify: No
Example of a HeaderTransform object illustrating the addition of two
customer headers, the replacement of any previously provided Accept-
Encoding header, and the removal of any previously provided
Authorization or Accept-Language headers:
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{
"add": [
{
"name": "X-custom-header1",
"value": "header-value 1"
},
{
"name": "X-custom-header2",
"value": "header-value 2"
}
],
"replace": [
{
"name": "Accept-Encoding",
"value": "gzip,deflate,br"
}
],
"delete": [
"Authorization",
"Accept-Language"
]
}
2.4.9. MI.HTTPHeader
The HTTPHeader object contains a name/value pair for an HTTP header
to add or replace in a request or response. The CDNI-MEL expression
language can be used to dynamically generate response values.
Property: name
- Description: Name of the HTTP header.
- Type: String
- Mandatory-to-Specify: Yes
Property: value
- Description: New value of the named HTTP header.
- Type: String. Either a static string or an expression using
[CDNI-MEL] to dynamically construct a header value from
elements of the HTTP request and/or response.
- Mandatory-to-Specify: Yes
Property: value-is-expression
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- Description: Flag to signal whether the value is a static
string literal or a [CDNI-MEL] expression that needs to be
dynamically evaluated.
- Type: Boolean
- Mandatory-to-Specify: No. The default is "False", indicating
that the value is a string literal and does not need to be
evaluated.
Example of an HTTPHeader illustrating a dynamically constructed
header value that equals the session parameter from the query string:
{
"name": "X-custom-response-header",
"value": "req.uri.query.session",
"value-is-expression": true
}
2.5. General Metadata
This section documents a set of general purpose GenericMetadata
objects whose use and interpretation may be specific to a CDN or Open
Caching system's implementation, enabling extensibility and service
differentiation for providers.
2.5.1. MI.ServiceIDs
CDN configurations typically have multiple tiers of identifiers that
group configurations by customer account to facilitate logging,
billing, and support operations. This structure supports two tiers
of identifiers (a serviceID which typically identifies a high level
customer's service, and a propertyID which typically represents a
logical grouping of a set of hosts within a customers' service. It
should be noted, however, that the interpretation of ServiceID and
PropertyID are implementation-specific, and may not be used by all
CDNs and Open Caching systems.
This metadata model extension allows for the association service
identifier metadata to a host or path match and to allow for these
IDs to be dynamically generated via an expression language. For
example, it may be necessary to extract a portion of the Request URI
path to derive a service identifier (e.g.: /news/* maps to one
propertyID and /movies/* maps to a different propertyID). When
processing the MI.ServiceIDs metadata for a request, implementations
SHOULD override any previously assigned service identifiers with
those specified by this metadata.
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MI.ServiceIDs is a new GenericMetadata object that allows for the
specification of the two tiers of CDN-specific service identifiers
and service names.
Property: service-id
- Description: A provider-specific identifier for the service
(typically a customer account identifier).
- Type: String. Either a literal (static string) or an
expression using CDNI-MEL to dynamically construct the ID from
elements of the HTTP request and/or response.
- Mandatory-to-Specify: No
Property: service-id-is-expression
- Description: Flag to signal whether the service-id is a static
string literal or a CDNI-MEL expression that needs to be
dynamically evaluated.
- Type: Boolean
- Mandatory-to-Specify: No. The default is "False", indicating
that the service-id is a string literal and does not need to be
evaluated.
Property: service-name
- Description: Human-readable name for the service-id.
- Type: String
- Mandatory-to-Specify: No
Property: property-id
- Description: A provider-specific identifier for the property
(typically identifies a child configuration within the parent
service-id).
- Type: String. Either a literal (static string) or an
expression using CDNI-MEL to dynamically construct the ID from
elements of the HTTP request and/or response.
- Mandatory-to-Specify: No
Property: property-id-is-expression
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- Description: Flag to signal whether the property-id is a static
string literal or a CDNI-MEL expression that needs to be
dynamically evaluated.
- Type: Boolean
- Mandatory-to-Specify: No. The default is "False", indicating
that the property-id is a string literal and does not need to
be evaluated.
Property: property-name
- Description: Human-readable name for the property-id.
- Type: String
- Mandatory-to-Specify: No
Example illustrating the assignment of a literal service-id along
with a dynamically computed property-id that is extracted from the
root element of the request URI path.
{
"generic-metadata-type": "MI.ServiceIDs",
"generic-metadata-value": {
"service-id": "12345",
"service-name": "My Streaming Service",
"property-id": "path_element(req.uri, 1)",
"property-id-is-expression": true
}
}
2.5.2. MI.PrivateFeatureList
The dCDN may gather a certain number of private features (i.e., not
[yet] adopted by SVA or considered marginal) that it may want to
expose to the content provider and/or the uCDN. Although private,
the announcement, selection, and configuration of this private
feature could be done through the OC API.
One example could be the support in OCNs of a new protocol that
allows the ability to get additional insight about the user agent
status (e.g., CTA Wave CMCD).
As another example, Broadpeak has developed a feature called
S4Streaming, and would like to give the opportunity to control that
feature to the uCDN.
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PrivateFeatureListis a GenericMetadata configuration object as a base
generic object that permits the control of private features.
Property: features
- Description: The list of feature configuration objects.
- Type: List (array) of MI.PrivateFeature objects .
- Mandatory-to-Specify: Yes
2.5.2.1. MI.PrivateFeature
MI.PrivateFeature object contains the following properties:
Property: feature-oid
- Description: The owner/organization that has specified that
feature.
- Type: String
- Mandatory-to-Specify: Yes
Property: feature-type
- Description: Indicates the type/name of the private feature
configuration object.
- Type: String
- Mandatory-to-Specify: Yes
Property: feature-value
- Description: Feature configuration object.
- Type: Format/type is defined by the value of the feature-type
property above.
- Mandatory-to-Specify: Yes
Note that the private features exposed by the dCDN can be advertised
through a dedicated FCI object.
Example, illustrating the Broadpeak S4 Streaming feature:
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{
"generic-metadata-type": "MI.PrivateFeatureList",
"generic-metadata-value": {
"feature": {
"feature-oid": "Broadpeak",
"feature-type": "S4Streaming",
"feature-value": {
"footprint": {
"footprint-type": "ipv4cidr",
"footprint-value": [
"192.0.2.0/24",
"198.51.100.0/24"
]
},
"activation": "ON",
"mode": "transparent",
"policy": "bandwidth-max"
}
}
}
}
2.5.3. MI.RequestRouting
The uCDN requires the ability to indicate whether HTTP redirect, DNS
redirect, and manifest rewrite are allowed, and indicate which is
preferable. This is required in cases where the uCDN would like to
delegate the traffic relying on the iterative method but knows the
client will not support HTTP redirect. In that case, the uCDN needs
a means to force the dCDN to perform request routing based on DNS
redirect (or manifest rewrite).
This configuration possibility is useful only if the dCDN can
advertise the mode of redirection it supports. There is an ongoing
discussion in the IETF CDNI group to understand the semantics behind
the redirection modes currently in Footprint & Capabilities
Advertising Interface (I-DNS and I-HTTP). It is not clear whether
this indicates that the dCDN supports one or both delegation modes
(the request routing performed by the uCDN can only be based on DNS
redirect or HTTP redirect or both), or whether it indicates that the
dCDN supports, as its own request routing mode, DNS redirect and/or
HTTP redirect. The latter is required for this new configuration
object to be valid.
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MI.RequestRouting is a new GenericMetadata object that allows the
uCDN to force the dCDN request routing mode(s) to be applied when
working in iterative redirection mode. The list of redirection modes
supported by the dCDN is advertised through the FCI.RedirectionMode
object. The list of request routing modes supported by the dCDN is
advertised through the FCI.RequestRoutingMode object.
Property: request-routing-modes
- Description: Instructs the dCDN to perform request routing
according to one or more preferred modes among those supported
and advertised by the dCDN through the FCI.RequestRouting
object. One must understand that forcing (instead of letting
the dCDN request router select) one particular request routing
mode may trigger some inefficiency in the request routing
process.
- Type: List (array) of iterative request routing modes
- Values: "DNS", "HTTP", "MANIFEST_REWRITE"
- Mandatory-to-Specify: No. By default, all request routing
modes supported by the dCDN can be used by the dCDN as part of
its request routing process.
Example, illustrating the uCDN forcing the dCDN to use DNS or HTTP as
the method for request routing in case the uCDN performs an iterative
delegation (i.e., iterative redirection mode):
{
"generic-metadata-type": "MI.RequestRouting",
"generic-metadata-value": {
"request-routing-modes": [ "DNS", "HTTP" ]
}
}
3. Metadata Expression Language
The CDNI Metadata Expression Language provides a syntax with a rich
set of variables, operators, and built-in functions to facilitate use
cases within the extended CDNi metadata model.
Enables expression matching to dynamically determine if
StageMetadata (Section 2.4) should be applied at a StageRules
match.
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Enables the dynamic construction of a value to be used in
scenarios such as constructing a service identifier or cache key,
setting an HTTP header, rewriting a request URI, setting a
response status code, or dynamically generating a response body
for a SyntheticResponse.
Expressions can evaluate to a Boolean, string, or integer, depending
on the use case:
+=============================+=================+==================+
| Usage | Description | Evaluation |
| | | Results |
+=============================+=================+==================+
| ExpressionMatch.expression | Dynamically | Boolean. |
| | determines if | Expressions that |
| | StageMetadata | do not evaluate |
| | should be | to True or False |
| | applied at a | shall be |
| | specific | considered as |
| | StageRules. | False. |
+-----------------------------+-----------------+------------------+
| RequestTransform.uri | Rewrites | String |
| | request URI | |
| | that will be | |
| | presented to | |
| | all downstream | |
| | stages. | |
+-----------------------------+-----------------+------------------+
| ResponseTransform.response- | Dynamically | Integer (HTTP |
| status | sets a response | status code) |
| | status code to | |
| | replace the | |
| | status-code | |
| | returned by the | |
| | origin. | |
+-----------------------------+-----------------+------------------+
| SyntheticResponse.response- | Dynamically | Integer (HTTP |
| status | sets a response | status code) |
| | status code for | |
| | a synthetically | |
| | constructed | |
| | response. | |
+-----------------------------+-----------------+------------------+
| SyntheticResponse.body | Dynamically | String |
| | constructs a | |
| | response body. | |
+-----------------------------+-----------------+------------------+
| HTTPHeader.value | Dynamically | String |
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| | constructs a | |
| | header value. | |
+-----------------------------+-----------------+------------------+
| ComputedCacheKey.expression | Dynamically | String |
| | constructs a | |
| | cache key. | |
+-----------------------------+-----------------+------------------+
| ServiceIDs.properry- | Dynamically | String |
| id,ServiceIDs.service-id | constructs | |
| | service and | |
| | property | |
| | identifiers. | |
+-----------------------------+-----------------+------------------+
Table 2: CDNI MEL expressions
3.1. Expression Variables
+=====================+====================================+
| Variable | Meaning |
+=====================+====================================+
| req.h.<name> | Request header <name> |
+---------------------+------------------------------------+
| req.uri | Request URI (includes query string |
| | and fragment identifier, if any) |
+---------------------+------------------------------------+
| req.uri.path | Request URI path |
+---------------------+------------------------------------+
| req.uri.pathquery | Request path and query string |
+---------------------+------------------------------------+
| req.uri.query | Request query string |
+---------------------+------------------------------------+
| req.uri.query.<key> | Request query string value |
| | associated with <key> |
+---------------------+------------------------------------+
| req.method | Request HTTP method (GET, POST, |
| | others) |
+---------------------+------------------------------------+
| resp.h.<name> | Response header <name> |
+---------------------+------------------------------------+
| resp.status | Response status code |
+---------------------+------------------------------------+
Table 3: CDNI MEL variables
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3.2. Expression Operators and keywords
+==========+==========+==========+=================================+
| Operator | Type | Result | Meaning |
| | | Type | |
+==========+==========+==========+=================================+
| == | infix | Boolean | Equality test |
+----------+----------+----------+---------------------------------+
| != | infix | Boolean | Inequality test |
+----------+----------+----------+---------------------------------+
| ! | infix | Boolean | Logical NOT operator |
+----------+----------+----------+---------------------------------+
| > | infix | Boolean | Greater than test |
+----------+----------+----------+---------------------------------+
| < | infix | Boolean | Less than test |
+----------+----------+----------+---------------------------------+
| >= | infix | Boolean | Greater than or equal test |
+----------+----------+----------+---------------------------------+
| <= | infix | Boolean | Less than or equal |
+----------+----------+----------+---------------------------------+
| *= | infix | Boolean | Glob style match |
+----------+----------+----------+---------------------------------+
| ~= | infix | Boolean | Regular expression match (see |
| | | | https://www.pcre.org/ for |
| | | | details on PCRE RegEx matching) |
+----------+----------+----------+---------------------------------+
| ipmatch | infix | Boolean | Match against IP address or |
| | | | CIDR (IPv4 and IPv6) |
+----------+----------+----------+---------------------------------+
| + | infix | Numeric | Addition |
+----------+----------+----------+---------------------------------+
| - | infix | Numeric | Subtraction |
+----------+----------+----------+---------------------------------+
| * | infix | Numeric | Multiplication |
+----------+----------+----------+---------------------------------+
| / | infix | Numeric | Division |
+----------+----------+----------+---------------------------------+
| % | infix | Unsigned | Modulus |
| | | or | |
| | | Integer | |
+----------+----------+----------+---------------------------------+
| . | infix | String | Concatenation |
+----------+----------+----------+---------------------------------+
| ? : | ternary | * | Conditional operator: <e> ? |
| | | | <v1> : <v2> Evaluates <v1> if |
| | | | <e> is true, <v2> otherwise. |
+----------+----------+----------+---------------------------------+
| ( ) | grouping | | Used to override precedence and |
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| | | | for function calls. |
+----------+----------+----------+---------------------------------+
Table 4: CDNI MEL expression operators
+=========+=======================================+
| Keyword | Meaning |
+=========+=======================================+
| and | Logical AND |
+---------+---------------------------------------+
| or | Logical OR |
+---------+---------------------------------------+
| not | Logical NOT (see also the ! operator) |
+---------+---------------------------------------+
| nil | No value (distinct from empty value) |
+---------+---------------------------------------+
| true | Boolean constant: true |
+---------+---------------------------------------+
| false | Boolean constant: false |
+---------+---------------------------------------+
Table 5: CDNI MEL expression keywords
3.3. Expression Built-in Functions
3.3.1. Basic Functions: Type Conversions
+============+=====================+=============+=========+
| Function | Action | Argument(s) | Returns |
+============+=====================+=============+=========+
| integer(e) | Converts expression | 1 | integer |
| | to integer. | | |
+------------+---------------------+-------------+---------+
| real(e) | Converts expression | 1 | real |
| | to real. | | |
+------------+---------------------+-------------+---------+
| string(e) | Converts expression | 1 | string |
| | to string. | | |
+------------+---------------------+-------------+---------+
| boolean(e) | Converts expression | 1 | Boolean |
| | to Boolean. | | |
+------------+---------------------+-------------+---------+
Table 6: CDNI MEL type conversions
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3.3.2. Basic Functions: String Conversions
+==========+==============================+=============+=========+
| Function | Action | Argument(s) | Returns |
+==========+==============================+=============+=========+
| upper(e) | Converts a string to | 1 | string |
| | uppercase. Useful for case- | | |
| | insensitive comparisons. | | |
+----------+------------------------------+-------------+---------+
| lower(e) | Converts a string to | 1 | string |
| | lowercase. Useful for case- | | |
| | insensitive comparisons. | | |
+----------+------------------------------+-------------+---------+
Table 7: CDNI MEL string conversions
3.3.3. Convenience Functions
+====================+======================================+===========+=======+
|Function |Action |Argument(s)|Returns|
+====================+======================================+===========+=======+
|match(string Input, |Regular expression Match is applied to|2 |string |
|string Match) |Input and the matching element (if | | |
| |any) is returned. Empty string is | | |
| |returned if there is no match. See | | |
| |https://www.pcre.org/ for details on | | |
| |PCRE RegEx matching. | | |
+--------------------+--------------------------------------+-----------+-------+
|match_replace(string|Regular expression Match is applied to|3 |string |
|Input, string Match,|Input arg and replaced with the | | |
|string Replace) |Replace arg upon successful match. | | |
| |Returns updated (replaced) version of | | |
| |Input. | | |
+--------------------+--------------------------------------+-----------+-------+
|add_query(string |Add query string element q with value |2 |string |
|Input, string q, |v to the Input string. If v is nil, | | |
|string v) |then just add the query string element| | |
| |q. The query element q and value v | | |
| |must conform to the format defined in:| | |
| |https://datatracker.ietf.org/doc/html/| | |
| |rfc3986 | | |
+--------------------+--------------------------------------+-----------+-------+
|remove_query(string |Remove (all occurrences of) query |2 |string |
|Input, string q) |string element q from the Input | | |
| |string. | | |
+--------------------+--------------------------------------+-----------+-------+
|path_element(string |Return the path element n from Input. |2 |string |
|Input, integer n) |-1 returns the last element. | | |
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+--------------------+--------------------------------------+-----------+-------+
|path_element(string |Return the path elements from position|3 |string |
|Input, integer n, |n to m. | | |
|integer m) | | | |
+--------------------+--------------------------------------+-----------+-------+
Table 8: CDNI MEL convenience functions
3.4. Error Handling
3.4.1. Compile Time Errors
To ensure reliable service, all CDNI Metadata configurations MUST be
validated for syntax errors before they are ingested into a dCDN.
That is, existing configurations should be kept as the live running
configuration until the new configuration has passed validation. If
errors are detected in a new configuration, the configuration MUST be
rejected. A HTTP 500 Internal Server Error should be returned with a
message that indicates the source of the error (line number, and
configuration element that caused the error).
Examples of compile-time errors:
1. Configuration does not parse relative to the CDNI Metadata JSON
schema
2. Unknown CDNI Metadata object referenced in the configuration
3. CDNI Metadata object parse error
a. Missing mandatory CDNI Metadata property
b. Unknown CDNI Metadata property
c. Incorrect type for a CDNI Metadata property value
4. CDNI-MEL
a. Unknown CDNI-MEL variable name referenced in an expression
b. Unknown CDNI-MEL operator, key-word, or functions referenced
in an expression
c. Incorrect number of arguments used in a CDNI-MEL expression
operator or function
d. Incorrect type of argument used in a CDNI-MEL expression
operator or function
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3.4.2. Runtime Errors
If a runtime error is detected when processing a request, the request
should be terminated, and a HTTP 500 'Internal Server Error' returned
to the caller. To avoid security leaks, sensitive information MUST
be removed from the error message before it is returned to an
external client. In addition to returning the HTTP 500 error, the
dCDN SHOULD log additional diagnostics information to assist in
troubleshooting.
Examples of runtime errors:
1. Failure to allocate memory (or other server resources) when
evaluating a CDNI-MEL expression
2. Incorrect runtime argument type in a CDNI-MEL expression. E.g.,
trying to convert a non-numeric string to a number
3.5. Expression Examples
3.5.1. ComputedCacheKey
Sets the MI.ComputedCacheKey to the value of the X-Cache-Key header
from the client request.
{
"generic-metadata-type": "MI.ComputedCacheKey",
"generic-metadata-value": {
"expression": "req.h.x-cache-key"
}
}
Sets the MI.ComputedCacheKey to the lowercase version of the URI.
{
"generic-metadata-type": "MI.ComputedCacheKey",
"generic-metadata-value": {
"expression": "lower(req.uri)"
}
}
3.5.2. ExpressionMatch
ExpressionMatch where the expression is true if the user-agent (glob)
matches *Safari* and the referrer equals www.example.com.
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{
"expression": "req.h.user-agent *= '*Safari*'
and req.h.referrer == 'www.example.com'"
}
3.5.3. ResponseTransform
Adds X-custom-response-header with a value equal to the value of
user-agent - host header.
{
"response-transform": {
"headers": {
"add": [
{
"name": "X-custom-response-header",
"value": "req.h.user-agent . ' - ' . req.h.host",
"value-is-expression": true
}
],
"response-status": "403"
}
}
}
Adds a Set-Cookie header with a dynamically computed cookie value
(concatenating user agent and host name) and forces a 403 response.
{
"response-transform":{
"headers":{
"add":[
{
"name":"Set-Cookie",
"value":"req.h.user-agent . ' - ' . req.h.host",
"value-is-expression":true
}
]
}
}
}
3.5.4. MI.ServiceIDs
Extracts the first path element from the URI. For example, if the
URI = /789/second/third/test.txt, property-id is set to the first-
path (789).
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{
"generic-metadata-type":"MI.ServiceIDs",
"generic-metadata-value":{
"service-id":"12345",
"service-name":"My Streaming Service",
"property-id":"path_element(req.uri, 1)",
"property-id-is-expression":true
}
}
4. CDNI Capabilities Extensions
Since not all dCDNs will be capable of supporting all the extensions
proposed in this document, they need the ability to inform uCDNs
about their capabilities. [RFC8008] (the CDNI Footprint &
Capabilities Interface) was designed for this purpose and is extended
here to express these new capabilities.
4.1. FCI Metadata Object
Whenever a capability is represented as a top-level GenericMetadata
object, a dCDN will be able to declare its support simply by
including that object name in the capability-value list of the
standard FCI.Metadata object.
For each of the new GenericMetadata objects documented within the SVA
Configuration Interface, the default assumption should be that the
capability is not supported by the dCDN unless named within the FCI
metadata object.
Example: A capabilities object declaring support for several of the
newly defined GenericMetadata types:
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{
"capabilities": [
{
"capability-type": "FCI.Metadata",
"capability-value": {
"metadata": [
"MI.SourceMetadataExtended",
"MI.ProcessingStages",
"MI.CrossoriginPolicy",
"MI.CachePolicy",
"MI.NegativeCachePolicy",
"MI.PrivateFeatureList",
"MI.RequestRouting"
]
},
"footprints": [
< Footprint Objects >
]
}
]
}
4.2. FCI Model Extensions
In most cases, the presence or absence of a GenericMetadata object
name in FCI.Metadata (as described above), is sufficient to convey
support for a capability. There are cases, however, where more fine-
grained capabilities declarations are required. Specifically, a dCDN
may support some, but not all, of the capabilities specified by one
of the new GenericMetadata objects. In these cases, new FCI objects
will be created to allow a dCDN to express these fine-grained
capabilities.
4.2.1. FCI.AuthTypes
The AuthTypes object is used to indicate the support of
authentication methods to be used for content acquisition (while
interacting with an origin server) and authorization methods to be
used for content delivery.
This specification document defines two new authentication methods
(see MI.Auth) while there is one authorization method currently under
specification in CDNI called [URI.signing]
Property: stage-metadata
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- Description: Specifies the set of StageMetadata to be applied
at the processing stage if the match expression evaluates to
"True" or is not present.
- Type: Array of StageMetadata objects, applied in order.
- Mandatory-to-Specify: Yes
Property: authe-types
- Description: List of supported authentication methods (possibly
required for content acquisition)
- Type: Array of strings
- Values: "AWSv4Auth", "HeaderAuth"
- Mandatory-to-Specify: No. No authentication method is
supported in this case.
Property: autho-types
- Description: List of supported authorization methods (possibly
required for content delivery)
- Type: Array of strings
- Values: "UriSigning"
- Mandatory-to-Specify: No. No authorization method is supported
in this case.
FCI.AuthTypes example:
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{
"capabilities": [
{
"capability-type": "FCI.AuthTypes",
"capability-value": {
"authe-types": [
"AWSv4Auth",
"HeaderAuth"
],
"autho-types": [
"UriSigning"
]
}
}
]
}
4.2.2. FCI.ProcessingStages
This object is used to signal the set of features that are supported
in relation to the ProcessingStages configuration object (see
MI.ProcessingStages). Those optional features depend on the CDNI-MEL
language support.
Property: features
- Description: List of supported optional processing stages
features. Note that these features all have some dependencies
on support of the CDNI MEL expression language.
- Type: Array of strings
- Values: "ExpressionMatch", "RequestTransform",
"ResponseTransform"
- Mandatory-to-Specify: No. None of these optional features are
supported in this case.
Example:
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{
"capabilities": [
{
"capability-type": "FCI.ProcessingStages",
"capability-value": {
"features": [
"ExpressionMatch",
"RequestTransform",
"ResponseTransform"
]
}
}
]
}
4.2.3. FCI.SourceMetadataExtended
This object is used to signal the supported features related to the
SourceMetadataExtended configuration object.
Property: load-balance
- Description: List of supported load balancing algorithms in
relation to the SourceMetadataExtended configuration object
(see MI.SourceMetadataExtended)
- Type: Array of strings
- Values: "random", "content-hash", "ip-hash
- Mandatory-to-Specify: No. load balancing is not supported among
sources.
If the FCI.SourceMetadtaExtended object is not exposed/advertised or
if the "load-balance" array is empty, the dCDN does not support the
usage of the load-balance property attached to the
SourceMetadataExtended configuration object (see
MI.SourceMetadataExtended).
Example:
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{
"capabilities": [
{
"capability-type": "FCI.SourceMetadataExtended",
"capability-value": {
"load-balance": [
"random",
"content-hash",
"ip-hash"
]
}
}
]
}
4.2.4. FCI.RequestRouting
This object is used by the dCDN to signal/announce the supported
request routing modes. This can be optionally used by the uCDN to
further select a subset of those modes when operating one of the
iterative delegation modes. See the section on the GenericMetadata
RequestRouting object..
Property: request-routing-modes
- Description: List of supported request routing modes by the
dCDN. This information is useful when the uCDN decides to
perform a delegation in iterative mode.
- Type: Array of strings
- Values: "DNS", "HTTP-R", "MANIFEST_REWRITE"
- Mandatory-to-Specify: No. If the dCDN does not advertise the
supported request routing modes, they are all supported by
default.
Example:
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{
"capabilities": [
{
"capability-type": "FCI.RequestRouting",
"capability-value": {
"request-routing-modes": [
"DNS",
"HTTP",
"MANIFEST_REWRITE"
]
}
}
]
}
4.2.5. FCI.PrivateFeatures
This object is used by the dCDN to signal/announce the list of
supported private features. See the section on the GenericMetadata
PrivateFeatureList object.
Property: features
- Description: The list of supported private feature
- Type: List nested objects of FCI.PrivateFeature
Example:
{
"capabilities": [
{
"capability-type": "FCI.PrivateFeatures",
"capability-value": {
"features": [
{
"feature-oid": "Broadpeak",
"feature-type": "S4Streaming"
}
]
}
}
]
}
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4.2.5.1. FCI.PrivateFeature
This object contains the following properties:
Property: feature-oid
- Description: The owner/organization that has specified the
feature.
- Type: String
- Mandatory-to-Specify: Yes
Property: feature-type
- Description: Indicates the type/name of the private feature
configuration object.
- Type: String
- Mandatory-to-Specify: Yes
4.2.6. FCI.OcnSelection
This object is used by the dCDN to signal/announce the supported OCN
types and/or their transport arrangement and/or medium supported by
OCNs.
Property ocn-delivery-list
1. Description: List of supported medium and/or transport
arrangements.
2. Type: Array of nested objects, each containing the following
properties:
o Property: ocn-medium
- Description: This property lists the supported mediums.
- Type: Array of strings. The following values are specified:
"SATELLITE"
- Mandatory-to-Specify: No
o Property: ocn-transport
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- Description: Instructs the dCDN to perform delegation operating
a particular transport arrangement. The following values are
specified: "MABR".
- Type: Array of strings
- Mandatory-to-Specify: No
.....Property: ocn-type-list
o Description: List of supported OCN types. Examples include: "HOME"
or "EDGE".
o Type: Array of strings
o Mandatory-to-Specify: No
5. IANA Considerations
5.1. CDNI Payload Types
This document requests the registration of the following entries
under the "CDNI Payload Types" registry hosted by IANA
+==============================+===============+
| Payload type | Specification |
+==============================+===============+
| MI.CachePolicy | RFCthis |
+------------------------------+---------------+
| MI.NegativeCachePolicy | RFCthis |
+------------------------------+---------------+
| MI.StaleContentCachePolicy | RFCthis |
+------------------------------+---------------+
| MI.CacheBypassPolicy | RFCthis |
+------------------------------+---------------+
| MI.ComputedCacheKey | RFCthis |
+------------------------------+---------------+
| MI.AllowCompress | RFCthis |
+------------------------------+---------------+
| MI.SourceMetadataExtended | RFCthis |
+------------------------------+---------------+
| MI.SourceExtended | RFCthis |
+------------------------------+---------------+
| MI.LoadBalanceMetadata | RFCthis |
+------------------------------+---------------+
| MI.HeaderAuth | RFCthis |
+------------------------------+---------------+
| MI.AWSv4Auth | RFCthis |
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+------------------------------+---------------+
| MI.CrossOriginPolicy | RFCthis |
+------------------------------+---------------+
| MI.AuthTokenMetadata (TBD) | RFCthis |
+------------------------------+---------------+
| MI.CertificateMetadata (TBD) | RFCthis |
+------------------------------+---------------+
| MI.OcnSelection | RFCthis |
+------------------------------+---------------+
| MI.RequestRouting | RFCthis |
+------------------------------+---------------+
| MI.ProcessingStages | RFCthis |
+------------------------------+---------------+
| MI.StageRules | RFCthis |
+------------------------------+---------------+
| MI.ExpressionMatch | RFCthis |
+------------------------------+---------------+
| MI.StageMetadata | RFCthis |
+------------------------------+---------------+
| MI.RequestTransform | RFCthis |
+------------------------------+---------------+
| MI.ResponseTransform | RFCthis |
+------------------------------+---------------+
| MI.SyntheticResponse | RFCthis |
+------------------------------+---------------+
| MI.HeaderTransform | RFCthis |
+------------------------------+---------------+
| MI.HTTPHeader | RFCthis |
+------------------------------+---------------+
| MI.ServiceIDs | RFCthis |
+------------------------------+---------------+
| MI.TrafficType | RFCthis |
+------------------------------+---------------+
| MI.LoggingMetadata (TBD) | RFCthis |
+------------------------------+---------------+
| MI.PrivateFeatureList | RFCthis |
+------------------------------+---------------+
| FCI.AuthTypes | RFCthis |
+------------------------------+---------------+
| FCI.ProcessingStages | RFCthis |
+------------------------------+---------------+
| FCI.SourceMetadataExtended | RFCthis |
+------------------------------+---------------+
| FCI.RequestRouting | RFCthis |
+------------------------------+---------------+
| FCI.PrivateFeatures | RFCthis |
+------------------------------+---------------+
| FCI.OcnSelection | RFCthis |
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+------------------------------+---------------+
Table 9: Payload Types
6. Security Considerations
This specification is in accordance with the CDNI Request Routing:
Footprint and Capabilities Semantics. As such, it is subject to the
security and privacy considerations as defined in Section 8 of
[RFC8006] and in Section 7 of [RFC8008] respectively.
7. Conclusion
This document presents requirements and extensions to the CDNI
metadata model to cover typical use cases found in the commercial CDN
and Open Caching ecosystems. By limiting the scope of these
extensions to new GenericMetadata objects, backward compatibility can
be maintained with any existing CDNI Metadata Interface
implementations.
8. References
8.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123,
DOI 10.17487/RFC1123, October 1989,
<https://www.rfc-editor.org/info/rfc1123>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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,
<https://www.rfc-editor.org/info/rfc7231>.
[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,
<https://www.rfc-editor.org/info/rfc8006>.
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[RFC8007] Murray, R. and B. Niven-Jenkins, "Content Delivery Network
Interconnection (CDNI) Control Interface / Triggers",
RFC 8007, DOI 10.17487/RFC8007, December 2016,
<https://www.rfc-editor.org/info/rfc8007>.
[RFC8008] Seedorf, J., Peterson, J., Previdi, S., van Brandenburg,
R., and K. Ma, "Content Delivery Network Interconnection
(CDNI) Request Routing: Footprint and Capabilities
Semantics", RFC 8008, DOI 10.17487/RFC8008, December 2016,
<https://www.rfc-editor.org/info/rfc8008>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8804] Finkelman, O. and S. Mishra, "Content Delivery Network
Interconnection (CDNI) Request Routing Extensions",
RFC 8804, DOI 10.17487/RFC8804, September 2020,
<https://www.rfc-editor.org/info/rfc8804>.
[URI.signing]
van Brandenburg, R., Leung, K., and P. Sorber, "URI
Signing for CDN Interconnection (CDNI)", 8 October 2019,
<http://www.ietf.org/internet-drafts/draft-ietf-cdni-uri-
signing-19.txt>.
[W3C] "Cross-Origin Resource Sharing",
<https://www.w3.org/TR/2020/SPSD-cors-20200602/>.
8.2. Informative References
[AWSv4Method]
"Authenticating Requests (AWS Signature Version 4)",
<https://docs.aws.amazon.com/AmazonS3/latest/API/sig-v4-
authenticating-requests.html>.
[OC-CI] Goldstein, G., Ed., Power, W., Bichot, G., and A. Siloniz,
"Open Caching - Configuration Interface Functional
Specification (Parts 1,2,3)", Version 0.1, 2 July 2021.
[RFC5861] Nottingham, M., "HTTP Cache-Control Extensions for Stale
Content", RFC 5861, DOI 10.17487/RFC5861, May 2010,
<https://www.rfc-editor.org/info/rfc5861>.
[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, <https://www.rfc-editor.org/info/rfc6707>.
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[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, <https://www.rfc-editor.org/info/rfc7336>.
[RFC7694] Reschke, J., "Hypertext Transfer Protocol (HTTP) Client-
Initiated Content-Encoding", RFC 7694,
DOI 10.17487/RFC7694, November 2015,
<https://www.rfc-editor.org/info/rfc7694>.
[SVA] "Streaming Video Alliance Home Page",
<https://www.streamingvideoalliance.org>.
Authors' Addresses
Glenn Goldstein
Lumen Technologies
United States of America
Email: glenng1215@gmail.com
Will Power
Lumen Technologies
United States of America
Email: wrpower@gmail.com
Guillaume Bichot
Broadpeak
France
Email: guillaume.bichot@gmail.com
Alfonso Siloniz
Telefonica
Spain
Email: alfonsosiloniz@gmail.com
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