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

   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
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   This Internet-Draft will expire on April 27, 2015.

 
 
 
 
 
 
 
 
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Copyright Notice

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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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