Resource Management in Service Chaining
draft-irtf-nfvrg-resource-management-service-chain-01

Abstract

This document specifies problem definition and use cases of NFV resource management in service chaining for path optimization, 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 constraints of NFV infrastructure.

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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on January 7, 2016.

Copyright Notice

Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Resource management in service chain
• 3.1. Resource scheduling among network services
• 3.2. Performance coupling within a service chain
• 3.3. Multiple policies and conflicts
• 3.4. Dynamic adaptation of service chains
• 4. Use cases
• 4.1. Fail-over
• 4.2. Load balancing
• 4.3. Path optimization
• 4.4. Traffic optimization
• 4.5. Energy efficiency
• 5. Framework
• 6. Applicability to SFC
• 6.1. Related works in IETF SFC WG
• 6.2. Integration in SFC control-plane architecture
• 7. Security Considerations
• 8. IANA Considerations
• 9. References
• 9.1. Normative References
• 9.2. 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), one or more VNF forwarding graphs (VNF-FGs; a.k.a. service chains) can be associated to the network service, each of which describes a network connectivity topology, by referencing VNFs and Virtual Links that connect them. One or more network forwarding paths (NFPs) can be built on top of such a topology, each defining an ordered sequence of VNFs and Virtual Links to be traversed by traffic flows matching certain criteria.

The network service is instantiated by allocating NFVI resources for VNFs and VLs which constitute the VNF-FGs. Thus, the capacity and performance of the network service depends on the state and attributes of the resources used for the VNF instances. While this brings a similar problem to the VM placement optimization in a cloud computing environment, it differs as one or more VNF instances are interconnected for a single network service. For example, if one of the VNF instances in the VNF-FG gets failed or overloaded, the whole network service also gets affected. Thus, the VNF instances need to be carefully placed during NS instantiation considering their connectivity within NFPs. They also need to be monitored and dynamically migrated or scaled at run-time to adapt to changes in the resources.

The resource placement problem in VNF-FGs matters not only to the performance and capacity of network services but also to the optimized use of NFVI resources. For example, if processing and bandwidth burden converges on the VNF instances placed in a specific NFVI-PoP, it may result in scalability problem of the NFV infrastructure. Thus care is encouraged to be taken in distributing load across local and external VNF instances at run-time.

This document addresses resource management problem in service chaining to optimize the NS performance and NFVI resource usage. It provides the relevant use cases of the resource management such as traffic optimization, failover, load balancing and further describes design considerations and relevant framework for the resource management capability that dynamically creates and updates NFP instances considering NFVI resource states for VNF instances and VL instances.

Note that this document mainly focuses on the resource management capability based on the ETSI NFV framework [ETSI-NFV-ARCH] but also studies contribution points to the work for control plane of SFC architecture [I-D.ietf-sfc-architecture] [I-D.ietf-sfc-architecture] [I-D.ww-sfc-control-plane].

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.
• NFVI-PoP: A location or point of presence that hosts NFV infrastructure
• VNF Forwarding Graph (VNF-FG): A NF forwarding graph where at least one node is a VNF.
• Network Forwarding Path (NFP): The sequence of hardware/software switching ports and operations in the NFV network infrastructure as configured by management and orchestration that implements a logical VNF forwarding graph "link" connecting VNF "node" logical interfaces.
• 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. Resource management in service chain

3.1. Resource scheduling among network services

In the NFV framework, network services are realized with NS instantiation procedures at which virtualized NFVI resources are assigned to the VNFs and VLs which constitute VNF-FGs of the network service. The NFVI resources are placed and located along the VNF-FG by NFV Orchestrator (NFVO) dynamically according to:

• Resource availability,
• Deployment templates which define resource requirements of NS instances and VNF instances to support KPIs (e.g., capacity and performance) of the network service, and
• Resource policies which define how to govern NFVI resources for NS instances and VNF instances (e.g., affinity/anti-affinity rules, scaling, and fault management) to support an efficient use of NFVI resources as well as KPIs of the network service.

In order to satisfy the deployment templates and resource policies, VNF-FGs of the network services need to be built by considering the state of NFVI resources for VNF instances (e.g., availability, throughput, load, disk usage) and VL instances (e.g., bandwidth, delay, delay variation, packet loss).

However, since the NFVI resources are shared by different network services and their deployment constraints are very different from each other, it is required to carefully schedule the NFVI resources for multiple network services to optimize their KPIs.

3.2. Performance coupling within a service chain

In NFV, a network service is composed of one or more virtualized network functions which are connected via virtual links along NFPs specified for a traffic flow for the network service. Thus, the performance of a network service is determined by the performance and capability of a coupling of VNF instances and VL instances. For example, if one of the VNF instances or VL instances of an NFP gets failed or overloaded, the whole network service also gets affected. Thus, the VNF instances need to be carefully placed during NS instantiation considering their connectivity within NFPs.

This performance coupling can be handled by considering deployment rules for affinity/anti-affinity, geography, or topological locations of VNFs; and QoS of virtual links.

Another important factor for virtual links is the inter-connectivity between different NFVI-PoPs, which is an enabler of resource sharing among different NFVI-PoPs. When the VNF instances of a network service are allocated at different NFVI-PoPs, the NFVI-PoP interconnect may be a bottleneck point which needs to be monitored to support KPIs of the service chain.

3.3. Multiple policies and conflicts

The NFVI resources for a network service should be allocated and managed according to a NS policy given in the network service descriptor (NSD), which describes how to govern NFVI resources for VNF instances and VL instances to support KPIs of the network service. The examples of NS policy are affinity/anti-affinity, scaling, fault and performance, geography, regulatory rules, NS topology, etc. Since network services may have different NS policies for their own deployment and performance, this may cause resource management difficult within the shared NFVI resources.

For network-wide (or NS-wide) resource management, NFVI policy (or network policy) can be also provided. It may describe the resource management policy for optimized use of infrastructure resources rather than the performance of a single network service. The examples of NFVI policy are NFVI resource access control, reservation and/or allocation policies, placement optimization based on affinity and/or anti-affinity rules, geography and/or regulatory rules, resource usage, etc.

Multiple administrative domains or subsystems may have different NFVI policies so that it may bring some conflicts when enforcing them in a global infrastructure. There could be a similar problem among NS policies and NFVI policies.

Note that the similar topics are being studied in [I-D.norival-nfvrg-nfv-policy-arch]

3.4. Dynamic adaptation of service chains

The performance and capability of NFVI resources may vary in time due to different uses and management policies of the resources. If some changes in the resources make the service quality unacceptable, the VNF instances can be scaled according to the given auto-scaling policies. But it's only for local quality of the VNF.

In order to provide optimized KPIs to network services, the NFP instances need to dynamically adapt to the changes of the resource state at run-time. The performance of the whole NFP instance should be measured by monitoring the resource state of VNF instances and VL instances. Based on the monitoring results, some VNF instances may be determined and relocated at different virtualized resources with better performance and capabilities.

4. Use cases

In this section, several (but not exhausted) use cases for resource management in service chaining are provided: fail-over, load balancing, path optimization, traffic optimization, and energy efficiency.

4.1. Fail-over

For service continuity, failure of a VNF instance needs to be detected and the failed one needs to be replaced with the other one which is available to use as per redundancy policy. 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

                +----------------------------------------------+ 
                |                                              |
                |       SFC  Control & Management Planes       |
        +-------|                                              |
        |       |                                              |
        C1      +------^-----------^-------------^-------------+
 +---------------------|C3---------|-------------|-------------+
 |      |            +----+        |             |             |
 |      |            | SF |        |C2           |C2           |
 |      |            +----+        |             |             |
 | +----V--- --+       |           |             |             |
 | |   SFC     |     +----+      +-|--+        +----+          |
 | |Classifier |---->|SFF |----->|SFF |------->|SFF |          |
 | |   Node    |<----|    |<-----|    |<-------|    |          |
 | +-----------+     +----+      +----+        +----+          |
 |                     |           |              |            |
 |                     |C2      -------           |            |
 |                     |       |       |     +-----------+ C4  |
 |                     V     +----+ +----+   | SFC Proxy |-->  |
 |                           | SF | |SF  |   +-----------+     |
 |                           +----+ +----+                     |
 |                             |C3    |C3                      |
 |  SFC Data Plane Components  V      V                        |
 +-------------------------------------------------------------+