| Internet-Draft | CDNI Capacity Insights Capability Advert | October 2021 |
| Ryan, et al. | Expires 25 April 2022 | [Page] |
Open Caching architecture is a use case of Content Delivery Networks Interconnection (CDNI) in which the commercial Content Delivery Network (CDN) is the upstream CDN (uCDN) and the ISP caching layer serves as the downstream CDN (dCDN). This document supplements to the CDNI Capability Objects defined in RFC 8008 and CDNI Metadata Objects in RFC 8006. The defined Capability Objects structure and interface for advertisments and managment of a downstream CDN capacity.¶
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The Streaming Video Alliance [SVA] is a global association that works to solve streaming video challenges in an effort to improve end-user experience and adoption. The Open Caching Working Group [OCWG] of the Streaming Video Alliance [SVA] is focused on the delegation of video delivery requests from commerical CDNs to a caching layer at the ISP's network. Open Caching architecture is a specific use case of CDNI where the commercial CDN is the upstream CDN (uCDN) and the ISP caching layer is the downstream CDN (dCDN). While delegating traffic from one CDN to the other, it is important to make sure that an appropriate amount of traffic is delegated. In order to achive that, the SVA Open Caching Capacity Insight Specification [OC-CII] defines a feedback mechanism to inform the delegator how much traffic is appropriate to delegate. The traffic level information provided by that interface will be consumed by entities, such as the Open Caching Request router [OC-RR], to help inform that entity's traffic delegation decisions. This document defines and registers CDNI Payload Types (as defined at section 7.1 of [RFC8006]). These Payload types are used for Capability Objects added to those defined at section 4 of [RFC8008], which are required for the Open Caching Capacity Insights Interface [OC-CII].¶
For consistency with other CDNI documents this document follows the CDNI convention of uCDN (upstream CDN) and dCDN (downstream CDN) to represent the commercial CDN and ISP caching layer respectively.¶
This document registers two CDNI Payload Types (section 7.1 of [RFC8006]) for the defined capability objects:¶
and describes usage of a CDNI Generic Metadata object:¶
The following terms are used throughout this document:¶
Additionally, this document reuses the terminology defined in [RFC6707], [RFC7336], [RFC8006], [RFC8007], [RFC8008], and [RFC8804]. Specifically, we use the following CDNI acronyms:¶
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.¶
In order to enable information exchange between a uCDN and a dCDN about acceptable levels of traffic to delegate, a design has been developed as follows:¶
In normal operation a uCDN will communicate with a dCDN, via an interface, to collect and understand any limits that a dCDN has set forth for traffic delegation from a uCDN. These limits will come in the form of metrics such as bits per second, requests per second, etc.. These limits can be thought of as Not to Exceed (NTE) limits.¶
The dCDN should provide access to a telemetry source of near real time metrics that the uCDN can use to track current usage and compare that to the limits the dCDN has put forth and adjust traffic delegation decisions accordingly to keep current usage under the specified limits. In summary, the dCDN will inform the uCDN of limits in how much traffic it should delegate towards the dCDN and then provide a telemetry source that the uCDN can use to track its current usage. This allows for a non ambiguous definition of what a particular limit means and how to track usage against it.¶
Limits that are communicated from the dCDN to the uCDN should be considered valid based on the TTL of the response. The intention is that the limits would be long lived and would represent a reasonable peak limit that the uCDN should target throughout the course of a time period defined by the TTL.¶
In the event that a dCDN needs to inform a uCDN of an update to a previously communicated limit, the dCDN will be able to leverage a uCDN callback endpoint to inform the uCDN of adjusted limits. The most common use case for this would be related to dCDN infrastructure issues which reduced the amount of capacity available.¶
In the inverse of the above, if a uCDN would like to ask a dCDN to reconsider a previously established limit, the uCDN can make a call to the dCDN API interface with a proposed limit. The dCDN can consider the requested limit and choose to send the uCDN an updated limit if it meets the dCDN criteria. This is an asynchronous process. When the uCDN sends the solicitation to the dCDN, the dCDN will acknowledge receipt of the request, but will process the request with no guarantee that it will trigger an update to any limits.¶
Section 5 of [RFC8008] describes the FCI Capability Advertisement Object, which contains a CDNI Capability Object as well as the capability object type (a CDNI Paylod Type). The section also defines the Capability Objects per such type. Below we define two additional Capability Objects.¶
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 an FCI message, then the mandatory-to-specify property MUST also be included.¶
The Telemetry Capability Object is used to define a list of telemetry sources made available by the dCDN to the uCDN. Telemetry data is being defined as near real time aggregated metics of dCDN utilization, such as bits per second egress, and should be specific to the uCDN and dCDN traffic delegation relationship. Telemetry data is uniqiely defined by a source id, a metrics name, along with the footprints that are associated with an FCI.Capability advertisement. Telemetry data is an important component for CDNI delegation. The reasons that Telemetry information is important to traffic delegation is as follows: In situations where there are mutiple delegations, a uCDN will need to incorporate usage information from it's dCDN in such as manner as to allow higher level uCDNs to gain vislibility into traffic that is being delegated to a dCDN. An example of this is if a Content Provider delegates traffic directly to a CDN, and that CDN decides to further delegate traffic to a dCDN, if the Content Provider polls the uCDN for traffic usage, without the uCDN integrating the Telemetry data of it's dCDN, any traffic the uCDN delegated would become invisible to the Content Provider. When defining a Capacity Limit, the meaning of a limit might be considered ambiguous if the uCDN and dCDN are defining current usage via different data sources. Having the dCDN provide a data source defining usage that both itself and the uCDN reference, allows a non ambiguous metric to use when determing current usage and how that compares to a limit¶
Property: sources¶
The Telemetry Source Object is built of an associated type, a list of exposed metrics, and type-specific configuration data.¶
Property: id¶
Property: type¶
Property: metrics¶
Property: configuration¶
Below are the listed valid telemetry source types. At the time of this draft, the type registry is limit to a single type of Generic. The intention of this type registry is to allow for future extension to reference a yet to be drafted specification for a CDNI Telemetry interface, which would standardize the definition, format,etc of Telemetry data between participants of a CDNI workflow.¶
| Source Type | Description |
|---|---|
| generic | An object which allows for advertisement of generic datasources |
The following shows an example of Telemetry Capability including 2 metrics for a source, that is scoped to a footprint.¶
"capabilities": [
{
"capability-type": "FCI.Telemetry",
"capability-value": {
"sources": [
{
"id": "capacity_metrics_region1",
"type": "generic",
"metrics": [
{
"name": "egress_5m",
"time-granularity": 300,
"data-percentile": 50,
"latency": 1500
},
{
"name": "requests_5m",
...
}
]
}
]
},
"footprints": [
<footprint objects>
]
}
]
¶
The Capacity Limits Capability Object enables the dCDN to specify traffic delegation limits to a uCDN within an FCI.Capabilities advertisement. The limits specified by the dCDN will inform the uCDN on how much traffic can be delegated to the dCDN. The limits specified by the dCDN should be considered Not To Exceed (NTE) limits. The limits should be based on near time telemetry data that the dCDN provides to the uCDN. In any instance where there are multiple limits, the uCDN must consider and honor all specified limits and use the most restrictive limit when applicable.¶
Property: total-limits¶
Property: host-limits¶
The Capacity Limit Object is a JSON object which will be used with the total-limits and host-limits objects.¶
Property: limit-type¶
Property: maximum-hard¶
Property: maximum-soft¶
Property: telemetry-source¶
Property: host¶
Below are listed the valid capacity limit types. Additional limits would need to be specified and extended into this list. The values specified here represent the types that were identified as being the most relevant metrics for the purposes of traffic delegation between CDNs.¶
| Limit Type | Units |
|---|---|
| egress | Bits per second |
| requests | Requests per second |
| storage-size | Total bytes |
| storage-objects | Count |
| sessions | Count |
| cache-size | Total bytes |
The Capacity Limit Telemetry Source Object refers to a specific metric within a Telementry Source.¶
The following shows an example of an FCI.CapacityLimits object.¶
"capabilities": [
{
"capability-type": "FCI.CapacityLimits"
"capability-value": {
"total-limits": [
{
"limit-type": "egress",
"maximum-hard": 50000000000,
"maximum-soft": 25000000000,
"telemetry-source": {
"id": "capacity_metrics_region1",
"metric": "egress_5m"
}
}
],
"host-limits": [
{
"host": "serviceA.cdn.example.com",
"limits": [
"limit-type": "egress",
"maximum-hard": 20000000000,
"maximum-soft": 10000000000,
"telemetry-source": {
"id": "capacity_metrics_region1",
"metric": "egress_service2_5m"
}
]
},
{
"host": "serviceB.cdn.example.com",
"limits": [
"limit-type": "egress",
"maximum-hard": 30000000000,
"maximum-soft": 15000000000,
"telemetry-source": {
"id": "capacity_metrics_region1",
"metric": "egress_service2_5m"
}
]
}
]
},
"footprints": [
<footprint objects>
]
}
]
¶
The MI.RequestedCapacityLimits Generic Metadata object, which is cross referenced in CDNI Metadata Model Extensions [OC-MME], is fully detailed within this document. To enable the uCDN to request changes in dCDN limits, a new metadata object is introduced. Using this object, a uCDN can request that a dCDN reconsider limits, as defined by an FCI.CapacityLimits advertisement. The MI.RequestedCapacityLimits object must be scoped within an MI.HostIndex object and as such must be scoped to a host. The host parameter value must be a CDN-Domain that the dCDN has been configured to accept requests for. It is the responsibility of the dCDN to make any required adjustments to the FCI.CapacityLimits.total-limits if any per host limit updates might exceed values specified via the FCI.CapacityLimits.total-limit. The requested limits must specify a footprint, and that footprint should be one in which the dCDN has advertised a capability to support.¶
Property: requested-limits¶
The Requested Limit Object is build of an associated type, a value assocaited with the type, and the footprints that the limit should be associated with.¶
The following shows an example of MI.RequestedCapacityLimits object.¶
{
"host": "serviceA.cdn.example.com",
"host-metadata": {
"metadata": [
...,
{
"generic-metadata-type": "MI.RequestedCapacityLimits",
"generic-metadata-value": {
"requested-limits": [
{
"limit-type": "egress",
"limit-value": 80000000000,
"footprints": [{
"footprint-type": "ipv4cidr",
"footprint-value": ["192.0.2.0/24", "198.51.100.0/24"]
}]
},
{
...
}
]
}
}
]
}
}
¶
simialr to the type definitions described in section 7.1 of [RFC8006] as well as the types described in section 6.1 of [RFC8008].¶
This document requests the registration of the three additional payload types:¶
| Payload Type | Specification |
|---|---|
| FCI.Telemetry | RFCthis |
| FCI.CapacityLimits | RFCthis |
| MI.RequestedCapacityLimits | RFCthis |
[RFC Editor: Please replace RFCthis with the published RFC number for this document.]¶
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.¶
The authors would like to express their gratitude to TBD for TBD (their guidance / contribution / reviews ...)¶