Resource Management for Dynamic Service Chain Adaptation
draft-lee-nfvrg-resource-management-service-chain-00

Abstract

This document specifies problem definition and use cases of dynamic service chain adaptation for traffic optimization, failover, load balancing, etc. It further describes design considerations and relevant framework for the resource management capability that dynamically creates and updates network forwarding paths (NFPs) considering resource state of VNF instances.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Dynamic service chain adaptation
• 3.1. Use cases
• 3.2. Design considerations
• 3.3. Framework
• 4. Related works in IETF SFC WG
• 5. Security Considerations
• 6. IANA Considerations
• 7. References
• 7.1. Normative References
• 7.2. Informative References
• Authors' Addresses

1. Introduction

Network Functions Virtualisation (NFV) [ETSI-NFV-WHITE] offers a new way to design, deploy and manage network services. The network service can be composed of one or more network functions and NFV relocates the network functions from dedicated hardware appliances to generic servers, so they can run in software. Using these virtualized network functions (VNFs), the network service can be described by a service chain (or VNF forwarding graph; VNF-FG) which defines an ordered sequence of VNFs for the composed service. The VNF-FG can be instantiated by creating or selecting VNF instances and virtual links (VLs) among them, which results in a network forwarding path (NFP).

The performance or state of the NFP depends on the ones of VNF instances and underlying NFVI resources. For example, if one of the VNF instances in a NFP gets failed, the whole network service using the NFP also gets failed. Thus, the VNF instances per NFP need to be carefully selected at VNF-FG instantiation or dynamically replaced by other VNF instances at run-time for better performance and resilience.

This document specifies problem definition and use cases for dynamic service chain adaptation for traffic optimization, failover, load balancing, etc. It further describes design considerations and relevant framework for the resource management capability that dynamically creates and updates NFPs considering resource state of VNF instances.

This document mainly focuses on the resource capability in the ETSI NFV framework [ETSI-NFV-ARCH] but also studies its applicability to the control plane of SFC architecture [I-D.ietf-sfc-architecture].

2. Terminology

This document uses the following terms and most of them were reproduced from [ETSI-NFV-TERM].

• Network Functions (NF): A functional building block within a network infrastructure, which has well-defined external interfaces and a well-defined functional behavior.
• Network service: A composition of network functions and defined by its functional and behavioural specification.
• NFV Framework: The totality of all entities, reference points, information models and other constructs defined by the specifications published by the ETSI ISG NFV.
• Virtualised Network Function (VNF): An implementation of an NF that can be deployed on a Network Function Virtualisation Infrastructure (NFVI).
• NFV Infrastructure (NFVI): The NFV-Infrastructure is the totality of all hardware and software components which build up the environment in which VNFs are deployed.
• NF Forwarding Graph: A graph of logical links connecting NF nodes for the purpose of describing traffic flow between these network functions.
• VNF Forwarding Graph (VNF-FG): A NF forwarding graph where at least one node is a VNF.
• Virtual Link: A set of connection points along with the connectivity relationship between them and any associated target performance metrics (e.g. bandwidth, latency, QoS). The Virtual Link can interconnect two or more entities (VNF components, VNFs, or PNFs).
• Scaling: Ability to dynamically extend/reduce resources granted to the Virtual Network Function (VNF) as needed.

3. Dynamic service chain adaptation

The goal of dynamic service chain adaptation is to optimize the performance of network services. To meet this goal, NFPs of the network services need to consider the state of NFV resources (such as VNF instances or virtual links) at construction. The NFPs also need to dynamically adapt to the changes of the resource state at run-time, such as availability, load, and topological locations of VNF instances. The adaptation of NFPs can be executed by monitoring the resource state of VNF instances and VLs and replacing the original VNF instances of the NFP with new VNF instances that constitute a NFP with better performance. This functionality can be a part of Orchestrator functional building block in the NFV framework [ETSI-NFV-MANO] but it needs further study.

3.1. Use cases

There are several use cases of dynamic service chain adaptation: fail-over, end-to-end service optimization, traffic optimization, load balancing, energy efficiency, and so on.

Fail-over

When one of VNF instances in a NFP gets failed to run due to failure of its VM or underlying network, the whole chain of network service also gets failed. For service continuity, the failure of VNF instance needs to be detected and the failed one needs to be replaced with the other one which is available to use. Figure 1 presents an example of the fail-over use case. A network service is defined as a chain of VNF-A and VNF-B; and the service chain is instantiated with VNF-A1 and VNF-B1 which are instances of VNF-A and VNF-B respectively. In the meantime, failure of VNF-B1 is detected so that VNF-B2 replaces the failed one for fail-over of the NFP.

                                                             
                +--------+                        +--------+   
                | VNF-B2 |                       #| VNF-B2 |###
   +--------+   +--------+           +--------+ # +--------+   
###| VNF-A1 |       _|_           ###| VNF-A1 |#      _|_      
   +--------+      (___)             +--------+      (___)     
  ___/    #       /     \      \    ___/            /     \    
 (___)+---#------+       +   ===}  (___)+----------+       +   
          #       \ ___ /      /                    \ ___ /    
          #        (___)                             (___)     
          #          |                                 |
          #     +--------+                        +--------+   
          ######| VNF-B1 |###        (failure)--> | VNF-B1 |   
                +--------+                        +--------+   

### NFP