Network Working Group Q. Xie Internet-Draft Motorola Expires: April 22, 2004 L. Yarroll TimeSys Corporation October 23, 2003 RSERPOOL Redundancy-model Policy draft-xie-rserpool-redundancy-model-01.txt 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. This Internet-Draft will expire on April 22, 2004. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This document defines RSERPOOL Redundancy-model Member Selection Policy parameter and the related procedures. This policy is designed to be flexible and capable of supporting a wide range of advanced redundancy models found in some high availability systems. The design uses the extensibility in RSERPOOL pool load sharing policy. Xie & Yarroll Expires April 22, 2004 [Page 1] Internet-Draft RSERPOOL Redundancy-model Policy October 2003 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Redundancy-model Member Selection Policy Parameter . . . . . . 3 4. Member Selection Procedures under Redundancy-model Policy . . 5 5. Examples for Implementing Various Redundancy Models . . . . . 6 5.1 2N Redundancy with Active/Standby Protection . . . . . . . . . 6 5.2 N+M Redundancy with Active/Standby Protection . . . . . . . . 6 5.3 N-way Redundancy with Active/Standby Protection . . . . . . . 7 5.4 N-way Redundancy with Active/Active Protection . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 Normative References . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . 9 Xie & Yarroll Expires April 22, 2004 [Page 2] Internet-Draft RSERPOOL Redundancy-model Policy October 2003 1. Introduction The pool member selection policy in RSERPOOL design [2][3] is both flexible and extensible. By observing the pool's member selection policy a pool user (PU) can accomplish a wide range of different load distribution schemes and communications strategies across the pool elements (PE) in the pool. Some most basic load distribution schemes, such as the round-robin and least used policies, are already defined in ASAP [1]. In this document, we define another member selection policy - Redundancy-model policy - in order to support a variety of more advanced redundancy models used in some high availability systems. 1.1 Definitions This document uses the following terms: Pool (or server pool): See [3]; Pool element (PE): See [3]; Pool user (PU): See [3]; ENRP namespace (or namespace): See [3]; ENRP namespace server (or ENRP server): See [3]; 2. Conventions The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [5]. 3. Redundancy-model Member Selection Policy Parameter This defines a new Member Selection Policy TLV structure that SHOULD be used to indicate the role of a PE in a high availability redundancy model. This definition follows the member selection policy extension rules described in Section 3.6? of [6] Xie & Yarroll Expires April 22, 2004 [Page 3] Internet-Draft RSERPOOL Redundancy-model Policy October 2003 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0x6 | Length = variable | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Policy=0x5 | (reserved) | HA Role | Service State | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : Backup PE Identifier Parameter (optional) : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Type, Length, and Policy fields are defined in Section 3.6? in [6], with the addition of the following new Policy value: Value Policy ----- --------- 0x5 HA Redundancy-model support Other fields are defined as follows: High Availability (HA) role: 8 bits (unsigned integer) Indicating the role of the corresponding PE in the HA redundancy model. The following HA roles are currently defined: Value HA state ----- --------- 0x1 No role 0x2 Standby 0x3 Active 0x4 Dual role other values are reserved by IETF and MUST NOT be used. Service State: 8 bit (unsigned integer) Indicating the current service state elected by the corresponding PE. The following service states are currently defined: Value Service state ----- ------------- 0x1 In service 0x2 Stopping other values are reserved by IETF and MUST NOT be used. Xie & Yarroll Expires April 22, 2004 [Page 4] Internet-Draft RSERPOOL Redundancy-model Policy October 2003 Backup PE Identifier Parameter: This TLV is used in some redundancy models to indicate the designate backup of this PE. The format of PE Identifier Parameter is defined in [6] More detailed description of the HA states and Service states is given in the following sections. 4. Member Selection Procedures under Redundancy-model Policy When sending to a pool of Redundancy-model policy, a PU MUST use the following rules to select the recipient of the message: 1. When sending a new message for the first time to the pool, the PU SHOULD select a PE whose HA role is either "Active" or "Dual role" and service state is "In service." If more than one PEs in the pool meets these criteria, the PU SHOULD select one of them as the recipient of this message in a round-robin fashion. 2. When the PU is re-sending a message which was previously sent to a PE (PE_A) in the pool but failed because PE_A is found unreachable (i.e., a fail-over case), the PU SHOULD select a qualified backup PE as the message recipient, by following the steps below: A. First check if PE_A has a designated backup PE, whose presence and PE Id are indicated by the presence of the "Backup PE Identifier Parameter" in the Member Selection Policy TLV of PE_A. B. If no backup is designated by PE_A, the PU SHOULD select a PE whose HA role is either "Standby" or "Dual role", and service state is "In service." If no such PE can be found in the pool, the PU SHOULD abort re-sending the message and notify the application about the failure. If multiple PEs exist in the pool that meet these criteria, the PU SHOULD select one of them in a round-robin fashion. C. If a backup (PE_B) is designated by PE_A and exists in the pool and its service state is "In service", the PU SHOULD select PE_B as the recipient of the message being re-sent, regardless of the HA state of PE_B. D. If a backup (PE_B) is designated by PE_A but does not exist in the pool (i.e., the PE Id in the "Backup PE Identifier Parameter" in PE_A dose not match any PE in the pool), the PU SHOULD abort re-sending the message and notify the Xie & Yarroll Expires April 22, 2004 [Page 5] Internet-Draft RSERPOOL Redundancy-model Policy October 2003 application about the failure. E. If a backup (PE_B) is designated by PE_A and exists in the pool but its service state is NOT "In service", the PU SHOULD attempt to find a qualified backup for PE_B, by recursively invoking the above steps. In the case where the failed PE does not have a designated backup and the sending PU has succeeded in finding a qualified backup PE for the failed PE using the above procedures, the PU MAY keep a record of its finding and use the same backup for all subsequent fail-over events that may occur on the same failed PE. 5. Examples for Implementing Various Redundancy Models 5.1 2N Redundancy with Active/Standby Protection In this redundancy model there are two PEs registered in the pool; one has its HA role set to Active and the other's set to Standby. The active PE is providing the service while the standby PE is prepared to take over the active role should the active PE fail. In this redundancy model, the active PE does not have to have a designated backup, i.e., it does not need to include a "Backup PE Identifier Parameter" in its selection policy TLV when registering. 5.2 N+M Redundancy with Active/Standby Protection This redundancy model allows flexible active-standby relationships to be defined between the PEs in a pool. A pool with the N+M redundancy model consists of N PEs registered with their HA role set to Active (active PEs) and M PEs registered with their HA role set to Standby (standby PEs). Normally, the value of M is less than or equal to N, which means that a single PE can act as a standby for several active PEs at a time. A common use of the N+M redundancy model is N+1 redundancy. This is a special case of the N+M redundancy model. In the pool using N+1 redundancy, a single PE acts as a standby for all active PEs. In operation, the active PEs are provided the service while the standby PEs are prepared to become backup to any of the active PEs, should one or more of them fails. In this redundancy model, the active PEs do not have to have a designated backup, i.e., they do not need to include a "Backup PE Identifier Parameter" in their selection policy TLV when registering. Xie & Yarroll Expires April 22, 2004 [Page 6] Internet-Draft RSERPOOL Redundancy-model Policy October 2003 5.3 N-way Redundancy with Active/Standby Protection In this redundancy model, there are N (an even number) PEs in the pool. The PEs are paired to form N/2 active/standby pairs. In each pair, the active PE is providing the service while the standby PE is prepared to take over the active role should the active PE fail. Load is distributed across the N/2 active PEs. To implement such a pool, at registration each active PE needs to set its HA role to Active and indicate its designated backup by including a "Backup PE Identifier Parameter" in its selection policy TLV that contains the PE id of the backup. The standby PEs simply register with their HA role set to Standby and omit the "Backup PE Identifier Parameter." 5.4 N-way Redundancy with Active/Active Protection In this redundancy model there are one or more PEs in the pool, and are registered with their HA role set to Dual role. All PEs in the pool are actively providing service and are prepared to backup others at the same time. Note, this redundancy model can also be implemented (in some cases more efficiently) by using other active/active member selection policies such as the Round Robin and Weighted Round Robin policies (see Section 4.5.2? [1]). 6. IANA Considerations A new RSERPOOL Member Selection Policy type (HA Redundancy-model support: 0x5) will need to be registered with IANA. Additionally, the IETF reserved values specified in this document will need to be managed by IANA. 7. Security Considerations TBD 8. Acknowledgements The authors wish to thank Randy Presuhn and others for their review and comments. Normative References [1] Stewart, R., Xie, Q., Stillman, M. and M. Tuexen, "Aggregate Server Access Protocol (ASAP)", draft-ietf-rserpool-asap-08 (work in progress), October 2003. Xie & Yarroll Expires April 22, 2004 [Page 7] Internet-Draft RSERPOOL Redundancy-model Policy October 2003 [2] Tuexen, M., Xie, Q., Stewart, R., Shore, M., Ong, L., Loughney, J. and M. Stillman, "Requirements for Reliable Server Pooling", RFC 3237, January 2002. [3] Tuexen, M., Xie, Q., Stewart, R., Shore, M. and J. Loughney, "Architecture for Reliable Server Pooling", draft-ietf-rserpool-arch-07 (work in progress), October 2003. [4] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [5] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [6] Stewart, R., Xie, Q., Stillman, M. and M. Tuexen, "Aggregate Server Access Protocol (ASAP) and Endpoint Name Resolution (ENRP) common parameters document", draft-ietf-rserpool-common-param-05 (work in progress), October 2003. Authors' Addresses Qiaobing Xie Motorola, Inc. 1501 W. Shure Drive, 2-F9 Arlington Heights, IL 60004 US Phone: +1-847-632-3028 EMail: qxie1@email.mot.com La Monte H.P. Yarroll TimeSys Corporation 925 Liberty Avenue Pittsburgh, PA 15122 USA Phone: +1-412-325-6391 EMail: piggy@acm.org Xie & Yarroll Expires April 22, 2004 [Page 8] Internet-Draft RSERPOOL Redundancy-model Policy October 2003 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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