Internet DRAFT - draft-aranda-vnfpool-cdn-use-case
draft-aranda-vnfpool-cdn-use-case
Network working group P.A. Aranda
INTERNET-DRAFT Telefonica
Intended Status: Informational D. King
Expires: April 27, 2015 Lancaster University
M. Fukushima
KDDI R&D Labs
October 27, 2014
Virtualization of Content Distribution Network Use Case
draft-aranda-vnfpool-cdn-use-case-00
Abstract
This use case document provides requirements for moving Content
Distribution Networks (CDNs) from physical servers to a virtualized
environment. This new kind of CDN, known as virtualized CDN (vCDN),
allows for new constructs that simplify the CDN architecture. The
main elements of the CDN are analyzed with regards to the degree of
elasticity demanded from them in terms of computation, storage and
network resources.
This use case document provides resiliency requirements for
virtualization of the Content Distribution Network, known as
virtualized CDN (vCDN).
Status of This Memo
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Defining Resilience . . . . . . . . . . . . . . . . . . . . 3
1.1.1 Resiliency for stateless services . . . . . . . . . . . 3
1.1.2 Resiliency for stateful services . . . . . . . . . . . . 3
1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
2 vCDN Use Case . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Terms and definitions . . . . . . . . . . . . . . . . . . . 4
2.2 Content Distribution Network Components . . . . . . . . . . 5
2.2.1 Cache Node . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.2 CDN Controller . . . . . . . . . . . . . . . . . . . . . 6
2.2.3 CDN Load Balancer . . . . . . . . . . . . . . . . . . . 6
2.2.4 Surrogate Server . . . . . . . . . . . . . . . . . . . . 6
2.2.5 Content Proxy . . . . . . . . . . . . . . . . . . . . . 6
2.2.6 Content Peering Gateway . . . . . . . . . . . . . . . . 7
2.3 vCDN Resiliency Requirements . . . . . . . . . . . . . . . . 7
2.4 Service Degradation . . . . . . . . . . . . . . . . . . . . 7
2.5 Applicability of Virtual Network Function Pool (VNFPool) . . 7
2.6 Coexistence of Virtualized and Non-virtualized Network
Functions . . . . . . . . . . . . . . . . . . . . . . . . . 8
3 Security Considerations . . . . . . . . . . . . . . . . . . . . 9
4 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 9
5 References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1 Normative References . . . . . . . . . . . . . . . . . . . 9
5.2 Informative References . . . . . . . . . . . . . . . . . . 9
6. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1 Introduction
Delivery of content, especially of video, is one of the major
challenges of all operator networks due to massive growing amount of
traffic.
Growth of video traffic is driven by the shift from broadcast media
to unicast delivery via IP. This is also complementary to the growth
of today's video on demand traffic.
Additional on-demand content services to Internet end-users, have
similar quality constraints as video, high bandwidth and low latency,
and stored as close to users as possible.
A Content Delivery Network (CDN) represents a group of geographically
dispersed servers deployed to facilitate the distribution of
information generated by content providers in a timely and efficient
manner.
As physical functions, including CDN components, are migrated to
virtual platforms, Virtual Network Functions (VNF), a critical aspect
will be ensuring the VNF is resilient. Maintaining that resilience,
especially, when virtual resources are dynamically migrated and
managed will require co-ordination between VNFs.
This document discusses the key network resilience objectives for the
virtualized CDN. It outlines the challenges and risks for the
appropriate resilience requirements to negate or ensure minimal
impact of CDN-based services.
1.1 Defining Resilience
In the context of this I-D resiliency will ensure the ability to
provide and maintain an acceptable level of service or function to
the user, in the event of faults and challenges to normal
operation.
1.1.1 Resiliency for stateless services
In the case of services that do not require maintaining state
information, it is sufficient to move the VNF offering that service
to a new Virtual Machine (VM) or hardware entity.
1.1.2 Resiliency for stateful services
When a VNF is moved e.g., for failure mitigation, maintenance or
workload consolidation, the offered service and its performance can
be maintained, which is regarded as "service continuity" by those
entities which are using it.
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2 vCDN Use Case
2.1 Terms and definitions
CDN Provider: The service provider who operates a CDN and offers a
service of content delivery, typically used by a Content Service
Provider or another CDN Provider.
Content: Any form of digital data. One important form of Content
with additional constraints on distribution and delivery is
continuous media (i.e., where there is a timing relationship between
source and sink).
Content Delivery Network (CDN): The network infrastructure in which
the network elements cooperate at Layers 4 through 7 for more
effective delivery of Content to Users.
Network Service Provider (NSP): Provides network-based connectivity
and services to Users.
Over-the-top (OTT): A service, e.g., content delivery using a CDN,
operated by a different operator than the Operator to which the users
of that service are attached.
Service Continuity: ensure that if a service needs to be relocated to
another site due to an anomaly event (e.g. CPU overload, hardware
failure or security threat). The configuration of the VNF (e.g. IP
address) is preserved; thus (ideally) there is no impact on the end
user or node.
Users: The end user that interacts with a Content service. Such
communication is not restricted to HTTP and may be via a variety of
protocols. Examples of Users include: browsers, Set Top Boxes
(STBs), dedicated content applications (e.g., media players), etc.
2.2 Content Distribution Network Components
A number of functional components exist for deployment and operation
of Content Distribution Networks (CDN), these include:
o Content Cache Node to deploy content as close to each user as
possible;
o Content Controller to route the users request for content to the
closest available content store or content engine;
o Content Load Balancing to distribute user requests across one or
multiple servers;
o Surrogate Servers for mirrored web content servers;
o Content Proxies;
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o Content DNS Servers;
o GeoIP Information Servers;
o Content Peering Gateways.
In many CDN deployments, CDN nodes are dedicated physical appliances
or software with specific requirements on standard but dedicated
hardware. Often physical appliances and servers for different
purposes are deployed side-by-side. This comes with a number of
disadvantages:
o The capacity of the devices needs to be designed for peak hours
(typically on weekend evenings). During weekdays and business
hours, the dedicated hardware appliances and CDN servers are mainly
unused.
o It is not possible to react on unforeseen capacity needs e.g. in
case of a live-event as hardware resources need to be deployed in
advance.
o The average peak utilization and resilience of CDN nodes for
dedicated purposes or from different partners is lower as it could
be if the hardware resources would be shared between virtual
appliances on the same infrastructure.
o Dedicated physical devices and servers from several parties drive
the complexity of the operator network and increase the operational
expenses.
o Content delivery is a very volatile market driven by new content
formats, protocols, device types, content protection requirements
etc. Dedicated designed hardware hinders the necessary flexibility
to react on these changes.
o Content Delivery may imply some Value Added Services, e.g., for
Security concerns or for optimizing Performances. It may be
valuable for the Network Operator to rely on Outsourcing of a
Partner's solution rather than having to operate its own solution.
Therefore, it is important for CDNs to offer service continuity to
users during partial failures of key CDN elements, including: load
balancers, proxies and surrogate servers.
2.2.1 Cache Node
Operators to deploy their proprietary cache nodes into the ISP
network. CDN cache nodes are dedicated physical appliances or
software with specific requirements on standard but dedicated
hardware.
2.2.2 CDN Controller
A CDN controller objective is to select a cache node (or a pool of
cache nodes) for answering to the end-user request, and then redirect
the end-user to the selected Cache Node.
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The Cache Node shall answer to the end-user request and deliver the
requested content to the end user.
The CDN controller is a centralized component, and CDN cache nodes
are distributed within the Network and in multiple locations.
2.2.3 CDN Load Balancer
A CDN Load balancer objective is to distribute the demand to
different nodes in the CDN taking into account different criteria
including geographical proximity, network-wise proximity (number of
hops, policies set by the operator like ASN, etc.) or
load/performance parameters of the servers in the CDN. Additionally,
the CDN load balancer also provides resilience and protection against
contents server failure.
2.2.4 Surrogate Server
The CDN surrogate server interacts with other elements of the CDN for
the control and distribution of content within it and with User
Agents for the delivery of the content to the users. This behaviour
corresponds with the surrogate in the WWW context as defined in
[RFC3040]. The surrogate server provides resilience and protection
against contents server failure.
2.2.5 Content Proxy
The content proxy is a server that acts as an intermediary for
requests from clients seeking resources from the CDN content servers.
The content proxy provides resilience and protection against contents
server failure.
2.2.6 Content Peering Gateway
The content peering gateway is the element that interconnects
different CDNs [RFC7337]. This element is a single point of failure.
2.3 vCDN Resiliency Requirements
[TBD - Pedro & Dan]
2.3.1 Automatic scale-out/scale-in for unpredictable traffic variation
One of the significant benefits of virtualization for CDN Providers
is the elasticity of resource provisioning. This enables the CDN
Providers to mitigate unpredictable traffic variation. Due to the
unpredictability, the elastic resource management such as scaling
out/scaling in should be automatically performed by Service Control
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Entity and Pool Manager, rather than manually performed by human
operators.
2.3.2 Quality assurance of content delivery
Since the quality of content delivery service is a key performance
indicator of CDN Providers, it is crucial to assure the quality
during the process of scaling as well as after the completion of
scaling. In particular, geographical locations of added/remaining
Cache Nodes should be taken into account. This is because these
geographical locations have significant impacts on the quality of
content delivery.
2.3.3 Minimum impact on interconnection interfaces
Interconnections between CDNs [RFC7336] have been
recognized as a new opportunity of value creation for CDN
Providers. In order for vCDN to foster this opportunity further,
vCDN should minimize its impact on the interconnection interfaces
between CDNs. In particular, scaling in/scaling out vCDN should
not require any change of the architecture, protocols, and IP
addresses/DNS names of interconnection points.
2.4 Service Degradation
CDN-based services will require suitable monitoring of performance
metrics for delivering content. These include:
o Connection time
o DNS lookup time
o Download time
o First byte response
o Latency
o Page load time
o Response to request time
o Throughput
o Error Rate
o Packet Loss
o Uptime
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In the event of failure or service degradation, the ability to switch
between comparative VNFs will be required.
2.5 Applicability of Virtual Network Function Pool (VNFPool)
The use case reveals the potential of VFNPOOL in simplifying the CDN
architecture. Today's cache farms could be simplified in the way they
are deployed and handled. Imagine you deploy a cache for a certain
contents (e.g. newspaper web site) as a VNF. (This, as such, is a
compelling use case, because the granularity is much finer and you
might lower the minimum requirements for deploying a cache.)
The VFNPOOL protocol would control the way the VNF is deployed onto
the VNFPOOL. Then, during its lifetime, it would control how it
scales in or out.
Finally, it would also control the way the VNF is decommissioned.
Apart from scaling in and out, the VNFPOOL protocol would also check
for integrity and control the way a VNF can jump into another for
resilience reasons.
This second kind of control should include state transfer and
synchronization from the life to the backup VNF in some cases.
2.6 Coexistence of Virtualized and Non-virtualized Network Functions
With a CDN designed as loosely coupled software components a variety
of scenarios of co-existing virtualized and non-virtualized
components are possible.
Given that the CDN Controller is able to control Cache nodes deployed
on virtualized and non-virtualized server instances in parallel the
following scenarios are possible:
o More centralized located Cache nodes can run on virtualized (Cloud)
resources while Cache Nodes distributed deeper into the network
might run on physical appliances for operational reasons.
o Centralized cache cluster might run on dedicated non-virtualized
server for performance reasons while Cache node instances
distributed within in the network are running on virtualized
resources available in other network devices
o Within a migration scenario from non-virtualized to virtualized the
legacy cache nodes can be kept in production until the end of their
hardware life-cycle is reached (i.e. operation efficiency is still
sufficient) while new capacity is added to the CDN by deploying the
same software on virtualized resources.
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3 Security Considerations
<Security considerations text TBD>
4 IANA Considerations
<IANA considerations text TBD>
5 References
5.1 Normative References
5.2 Informative References
[RFC3040] Cooper, I., Melve, I., and G. Tomlinson, "Internet Web
Replication and Caching Taxonomy", RFC 3040, January 2001.
[RFC7337] Peterson, L., Davie, B., and R. Brandenburg, "Framework
for CDN Interconnection", RFC7337, June 2014.
[RFC7336] L. Peterson, B. Davie, and R. van Brandenburg, Ed.,
"Framework for Content Distribution Network
Interconnection (CDNI)", RFC 7336, August 2014.
[zong-vnfpool-problem-statement] Zong, N., "Problem Statement for
Reliable Virtualized Network Function (VNF) Pool", January
2014.
[TRILOGY2] The trilogy2 Consortium, "trilogy2: Building the Liquid
Net", http://trilogy2.eu/
6. Acknowledgement
This work is supported by the European FP7 Project
"Trilogy2" [TRILOGY2] under grant agreement 317756.
Authors' Addresses
Pedro A. Aranda
Telefonica, I+D; GCTO Unit
Spain
Email: pedroa.aranda@telefonica.com
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Daniel King
Lancaster University
UK
Email: d.king@lancaster.ac.uk
Masaki Fukushima
KDDI R&D Laboratories, Inc.
Japan
Email: fukusima@kddilabs.jp
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