High Availability mechanism for Service Function Chains
draft-xuan-sfc-chain-high-availability-00

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<Service Function Chaining>                              Truong-Xuan Do
Internet Draft                                             Younghan Kim
Intended status: Informational               Soongsil University, Korea
Expires:   April 2016                                      Oct 20, 2015

      High Availability mechanism for Service Function Chains
              draft-xuan-sfc-chain-high-availability-00

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Abstract

   This document describes mechanisms to achieve the high 
   availability of the service function chains. This document
   considers the high availability in the perspective of entire chain.
   This means the SFC control plane needs to take into account some 
   metrics related service chain in addition to individual service  
   functions. This document covers both stateless and stateful service
   functions as well.    

Table of Contents

   1. Introduction...................................................3
   2. Conventions used in this document..............................3
   3. High availability architecture of SFC..........................4
      3.1. Metrics for back-up SFPs..................................5
      3.2 SFP with all stateless service functions...................6
      3.3 SFP with stateful service funtions.........................7
   4. Security Considerations........................................8
   5. IANA Considerations............................................8
   6. References.....................................................8
      6.1. Normative References......................................8
      6.2. Informative References....................................8

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1. Introduction

   Service function chaining currently is redesigned with the support
   of the software-defined network (SDN) and network function 
   virtualization (NFV) which provide more flexible and dynamical 
   end-to-end services. 
   
   In order to ensure the high availability of service function 
   chains, some traditional mechanisms for individual service function
   are reused (e.g. Active/Standby or Active/Active). These mechanisms
   are based on the deployment of the backup or redundant service 
   functions. The recovery of whole service chain relies on the 
   recovery of individual service function. 
   
   This document describe a mechanism which ensure the high 
   availability of service chain based on some metrics of whole chain. 
   The mechanism also considers both stateless and stateful service
   functions in the chain. 

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [RFC2119].

        The terms about SFC are defined in [RFC7498] and 
        [I-D.ietf-sfc-architecture]

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3. High availability architecture of SFC
        
        Figure 1. shows the architecture for achieving the high 
        availability of the SFC. We make assumptions that each service 
    function has several instances which are connected to different 
        service function forwarders (SFF). Each service function path (SFP)
        is created by the combination of different service instances of 
        different service functions. We propose a new entity called SFC 
    HA manager which is responsible for monitoring metrics which belong
        not only to the individual service functions, such as fail-over, 
        load condition, but also the whole service chain, such as, latency,
        total load, and traffic engineering. The SFC HA Manager takes 
        responsibilities of making the backup SFPs. SFC HA manager should 
        be located in the control plane part [I-D.ietf-sfc-control-plane] 
        of SFC architecture 

    
                                                        [SFC HA Manager]
        
                 +****************+********+***>> back-up SFP
            +|.......+........|........|.........+.....>> current SFP
            ||       |        |        |         |   
                   SFI1     SFI2     SFI2     SFI3     SFI3
            |        |        |        |         |
            +---+----+        +----+---+         | 
                |                  |             | 
             SFFI1                                SFFI2        SFFI3  
                                        
                                Figure 1. High availability architecture of SFC

   

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3.1. Metrics for back-up SFPs
    
        Some metrics for whole service function chain are listed below:
        
        Fail-over: a back-up SFP with the replacement of failed service 
        functions
        
        Total latency: a back-up SFP with better latency 
        
        Total bandwidth: a back-up SFP with highest bandwidth
        
        Total path: a back-up SFP with shortest path
        
        Total load: a back-up SFP with the lowest load
        
        Traffic engineering: a back-up SFP with the pre-defined traffic 
        engineering goals 
        
 

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3.2 SFP with all stateless service functions
    
        Procedures for making a back-up service function path
        
        + Gather and monitor the states of current service function paths
        + Evaluate the current SFPs based on collected data and above
          metrics
        + HA manager makes back-up SFPs for current SFP
        + When a critical event occurs, the back-up SFP can be invoked and 
          replace the current SFP.
    + The information about new SFP (back-up) is updated to all 
          corresponding SFFs.
          
        

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3.3 SFP with stateful service funtions

    Procedures for making a back-up service function path
        
        + Gather and monitor the states of current service function paths
        + Evaluate the current SFPs based on collected data and above
          metrics
        + HA manager makes back-up SFPs for current SFP
                - For stateful service functions in the SFP, internal state
                  management for each service function is required and
                  synchronized with the same kind of service function when
                  creating a back-up SFP
                - State synchronization can be handled by the direct 
                  communication between two same kind service functions
                  
        + When a critical event occurs, the back-up SFP can be invoked and 
          replace the current SFP.
    + The information about new SFP (back-up) is updated to all 
          corresponding SFFs.

        

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4. Security Considerations

TBD.

5. IANA Considerations

TBD.

6. References

6.1. Normative References

   [RFC7498]
              Quinn, P. and T. Nadeau, "Problem Statement for Service 
                          Function Chaining", RFC 7498, April 2015.

6.2. Informative References

        [I-D.ietf-sfc-architecture]

              Halpern, J. and C. Pignataro, "Service Function Chaining
              (SFC) Architecture", draft-ietf-sfc-architecture-11 (work
              in progress), July 2015.
                          
        [I-D.ietf-sfc-control-plane] 
                           H. Li, Q. Wu, O. Huang, etc. al., "Service Function 
                           Chaining (SFC) Control Plane Components & Requirements",
                           draft-ietf-sfc-control-plane-00, Aug 2015

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Authors' Addresses

   Truong-Xuan Do
   Soongsil University
   4F Hyungnam Engineering Bldg. 424,
   (156-743) 511 Sangdo-Dong, Dongjak-Gu, Seoul, Korea

   Phone: +82 10 4473 6869
   Email: xuan@dcn.ssu.ac.kr

   Younghan Kim
   Soongsil University
   4F Hyungnam Engineering Bldg. 424,
   (156-743) 511 Sangdo-Dong, Dongjak-Gu, Seoul, Korea

   Phone: +82-2-820-0904
   Email: younghak@ssu.ac.kr

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