Network Working Group M. Tuexen INTERNET DRAFT Siemens AG Q. Xie Motorola R. Stewart M. Shore Cisco L. Ong Point Reyes Networks J. Loughney M. Stillman Nokia Expires October 2, 2001 April 2, 2001 Requirements for Reliable Server Pooling Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of [RFC2026]. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract The goal is to develop an architecture and protocols for the management and operation of server pools supporting highly reliable applications, and for client access mechanisms to a server pool. This document defines a basic set requirements for reliable server pooling. Tuexen et al. [Page 1] Internet Draft Requirements for Reliable Server Pooling April 2001 1. Introduction 1.1. Overview The Internet is always on. Many users expect services to be always available; many business depend upon connectivity 24 hours a day, 7 days a week, 365 days a year. In order to fulfill this, many proprietary solutions and operating system dependent solutions have been developed to provide highly reliable and highly available servers. This document defines requirements for reliable server pooling. Highly available services also put the same high reliability requirements upon the transport layer protocol beneath RSerPool - it must provide strong survivability in the face of network component failures. Supporting real time applications is another main focus of RSerPool which leads to requirements on the processing time needed. Scalability is another important requirement. RSerPool introduces new security vulnerabilities into existing applications, both in the pool formation and pool member selection process and in the failover process. Therefore, during the protocol development process it will be necessary to catalogue the threats to RSerPool and identify appropriate responses to those threats. 1.2. Terminology This document uses the following terms: Operation scope: The part of the network visible to pool users by a specific instance of the reliable server pooling protocols. Pool (or server pool): A collection of servers providing the same application functionality. Pool handle (or pool name): A logical pointer to a pool. Each server pool will be identifiable in the operation scope of the system by a unique pool handle or "name". Pool element: A server entity having registered to a pool. Tuexen et al. [Page 2] Internet Draft Requirements for Reliable Server Pooling April 2001 Pool user: A server pool user. Pool element handle (or endpoint handle): A logical pointer to a particular pool element in a pool, consisting of the name of the pool and a destination transport address of the pool element. Name space: A cohesive structure of pool names and relations that may be queried by an internal or external agent. Name server: Entity which the responsible for managing and maintaining the name space within the RSerPool operation scope. 1.3. Abbreviations PE: Pool element PU: Pool user SCTP: Stream Control Transmission Protocol TCP: Transmission Control Protocol 2. Requirements 2.1. Communication Model The general architecture should be based on a peer to peer model. However, the binding should be based on a client server model. 2.2. Processing Power It should be possible to use the protocol stack in small devices, like handheld wireless devices. The solution must scale to devices with a differing range of processing power. 2.3. Transport Protocol The protocols used for the pool handling should not cause network congestion. This means that it should not generate heavy traffic, even in case of failures, and has to use flow control and congestion avoidance algorithms which are interoperable with currently deployed techniques, especially the flow control of TCP [RFC793] and SCTP [RFC2960]. Therefore, for large pools, only a subset of all possible IP-addresses are returned by the name servers. Tuexen et al. [Page 3] Internet Draft Requirements for Reliable Server Pooling April 2001 The architecture should not rely on multicast capabilities of the underlying layer. Nevertheless, it can make use of it if multicast capabilities are available. Network failures have to be handled and concealed from the application layer as much as possible by the transport protocol. This means that the underlying transport protocol must provide a strong network failure handling capability on top of an acknowledged error-free non-duplicated data delivery service. The failure of a network element must be handled by the transport protocol in a way that the timing requirements are still fulfilled. 2.4. Support of RSerPool Unaware Clients Furthermore, it is expected that there will be a transition phase with some systems supporting the RSerPool architecture and some are not. To make this transition as seamless as possible it should be possible for hosts not supporting this architecture to use also the new pooling services via some mechanism. 2.5. Registering and Deregistering Another important requirement is that servers should be able to register to (become PEs) and deregister from a server pool transparently without an interruption in service. This means that after a PE has deregistered, it will continue to serve PUs, which started the connection before the deregistration of the PE. No PE will establish a new connection with the deregistered PE, because other PE of the server pool will be used. Servers should be able to register in multiple server pools which may belong to different namespaces. 2.6. Server Selection The RSerPool mechanisms must be able to support different server selection mechanisms. These are called server pool policies. Examples of server pool policies are: - Round Robin - Least used - Most used The set of supported policies must be extensible in the sense that new policies can be added as required. Tuexen et al. [Page 4] Internet Draft Requirements for Reliable Server Pooling April 2001 There must be a way for the client to provide information to the name server about the pool elements. The name servers should be extensible using a plug-in architecture. These plug-ins would provide a more refined server selection by the name servers using additional information provided by clients as hints. For some applications it is important that a client repeatedly connects to the same server in a pool if it is possible, i. e., if that server is still alive. This feature should be supported through the use of pool element handles. 2.7. Timing Requirements A server pool can consist of a large number (up to 500) of pool elements. This upper limit is important since the system will be used for real time applications. So handling of name resolution has to be fast. Another consequence of the real time requirement is the supervision of the pool elements. The name resolution should not result in a pool element which is not operational. 2.8. Failover Support The RSerPool architecture must be able to detect server failure quickly and be able to perform failover without service interruption. 2.9. Robustness The solution must allow itself to be implemented and deployed in such a way that there is no single point of failure in the system. 2.10. Naming Server pools are identified by pool handles. These pool handles are only valid inside the operation scope. Interoperability between different namespaces has to be provided by other mechanisms. 2.11. Scalability The RSerPool architecture should not require a limitation on the number of server pools or on the number of pool users. 2.12. Security Requirements Tuexen et al. [Page 5] Internet Draft Requirements for Reliable Server Pooling April 2001 2.12.1. General - The scaling characteristics of the security architecture should be compatible with those given previously. - The security architecture should support hosts having a wide range of processing powers. 2.12.2. Name Space Services - It must not be possible for an attacker to falsely register as a pool element with the name server either by masquerading as another pool element or by registering in violation of local authorization policy. - It must not be possible for an attacker to deregister a server which has successfully registered with the name server. - It must not be possible for an attacker to spoof the response to a query to the name server - It must be possible to prohibit unauthorized queries to the name server. - It must be possible to protect the privacy of queries to the name server and responses to those queries from the name server. - Communication among name servers must be afforded the same protections as communication between clients and name servers. 2.12.3. Security State The security context of an application is a subset of the overall context, and context or state sharing is explicitly out-of-scope for RSerPool. Because RSerPool does introduce new security vulnerabilities to existing applications application designers employing RSerPool should be aware of problems inherent in failing over secured connections. Security services necessarily retain some state and this state may have to be moved or re-established. Examples of this state include authentication or retained ciphertext for ciphers operating in cipher block chaining (CBC) or cipher feedback (CFB) mode. These problems must be addressed by the application or by future work on RSerPool. 3. Acknowledgements The authors would like to thank Bernard Aboba, Matt Holdrege, Christopher Ross, Werner Vogels and many others for their invaluable Tuexen et al. [Page 6] Internet Draft Requirements for Reliable Server Pooling April 2001 comments and suggestions. 4. References [RFC793] J. B. Postel, "Transmission Control Protocol", RFC 793, September 1981. [RFC959] J. B. Postel, J. Reynolds, "File Transfer Protocol (FTP)", RFC 959, October 1985. [RFC2026] S. Bradner, "The Internet Standards Process -- Revision 3", RFC 2026, October 1996. [RFC2608] E. Guttman et al., "Service Location Protocol, Version 2", RFC 2608, June 1999. [RFC2719] L. Ong et al., "Framework Architecture for Signaling Transport", RFC 2719, October 1999. [RFC2960] R. R. Stewart et al., "Stream Control Transmission Protocol", RFC 2960, November 2000. 5. Authors' Addresses Michael Tuexen Tel.: +49 89 722 47210 Siemens AG e-mail: Michael.Tuexen@icn.siemens.de ICN WN CS SE 51 D-81359 Munich Germany Qiaobing Xie Tel.: +1 847 632 3028 Motorola, Inc. e-mail: qxie1@email.mot.com 1501 W. Shure Drive, #2309 Arlington Heights, Il 60004 USA Randall Stewart Tel.: +1 815 477 2127 Cisco Systems, Inc. e-mail: rrs@cisco.com 24 Burning Bush Trail Crystal Lake, Il 60012 USA Tuexen et al. [Page 7] Internet Draft Requirements for Reliable Server Pooling April 2001 Melinda Shore Tel.: +1 607 272 7512 Cisco Systems, Inc. e-mail: mshore@cisco.com 809 Hayts Rd Ithaca, NY 14850 USA Lyndon Ong Tel.: +1 408 321 8237 Point Reyes Networks e-mail: long@pointreyesnet.com 1991 Concourse Drive San Jose, CA USA John Loughney Tel.: Nokia Research Center e-mail: john.loughney@nokia.com PO Box 407 FIN-00045 Nokia Group Finland Maureen Stillman Tel.: +1 607 273 0724 62 Nokia e-mail: maureen.stillman@nokia.com 127 W. State Street Ithaca, NY 14850 USA This Internet Draft expires October 2, 2001. Tuexen et al. [Page 8]