Network Working Group T. Dreibholz
Internet-Draft University of Duisburg-Essen
Expires: January 2, 2006 Jul 01, 2005
Applicability of Reliable Server Pooling for Real-Time Distributed
Computing
draft-dreibholz-rserpool-applic-distcomp-00.txt
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Copyright (C) The Internet Society (2005).
Abstract
This document describes the applicability of the Reliable Server
Pooling architecture to manage real-time distributed computing pools
and access the resources of such pools.
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1. Introduction
Reliable Server Pooling defines protocols for providing highly
available services. The services are located in a pool of redundant
servers and if a server fails, another server will take over. The
only requirement put on these servers belonging to the pool is that
if state is maintained by the server, this state must be transferred
to the other server taking over.
The goal is to provide server-based redundancy. Transport and
network level redundancy are handled by the transport and network
layer protocols.
The application may choose to distribute its traffic over the servers
of the pool conforming to a certain policy.
The scope of this document is to explain the way of using Reliable
Server Pooling mechanisms to manage and access pools of Distributed
Computing resources.
1.2 Terminology
The terms are commonly identified in related work and can be found in
the Aggregate Server Access Protocol and Endpoint Handlespace
Redundancy Protocol Common Parameters document ietf-rserpool-common-
param [11]
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2. Distributed Computing using RSerPool
2.1 Requirements
o Clients generate large computation jobs. Jobs have to be
processed by servers as soon as possible (real-time), i.e. unlike
concepts like SETI@home [14], it is not possible to let clients
fetch a job, process it later and may be some day upload the
result.
o Jobs may be partitionable, i.e. they can be split up to smaller
pieces which can be processed independently and the processing
results can be concatenated to the processing result of the
complete job. Jobs have to be processed by servers.
o Servers may be unreliable; i.e. user computers may be temporarily
added to the pool of computing resources and may be revoked when
they are used again by their owners. Furthermore, they may simply
disappear because of broken network connections (modems, etc.) or
power turned off.
o The processing power of servers in a pool of computing resources
may be very heterogeneous, i.e. a few supercomputers and many low-
end user PCs.
o It must be possible to manage large server pools, e.g. up to some
hundreds or even thousands of servers.
o Due to the heterogeneousity of the processing resources within a
pool, it must be possible to use appropriate server selection
procedures to meaningfully utilize the available resources.
o It must be possible to dynamically add and remove servers.
o Servers may be unreliable, especially when the servers are
represented by user PCs. Failover mechanisms are required to
continue an interrupted computation session.
2.1.1 Architecture
o An efficient implementation of the handlespace management
structures allows pools to contain thousands of elements.
Handlespace management structures have been proposed, implemented
and analyzed in [5].
o RSerPool allows to specify server selection rules by pool member
selection policies [12]. A set of adaptive and non-adaptive
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policies is already defined. To fulfill the requirements of new
applications, it is also possible to define new policies.
Research has already been made on the subject of load distribution
efficiency of pool policies in Distributed Computing scenarios:
see [3] for details.
o Dynamic addition and removal of PEs is a feature of RSerPool [9].
o The control/data channel concept [13] of RSerPool realizes a
session layer. That is, RSerPool already handles the main task of
maintaining and monitoring connections between PUs and PEs; the
only task of the application layer to provide full failover
functionality is to realize an application-dependent failover
procedure. By the usage of client-based state synchronization [2]
in the form of ASAP Cookies, a failover may be fully transparent
to the PU while only a state restoration is necessary on the PE
side. A demo application [1] using the RSerPool session layer in
a Distributed Computing application is described in [4].
2.1.2 Implementation
A proof of concept implementation of a Distributed Computing
application based on the RSerPool prototype rsplib can be found at
[1]. This system provides a fractal graphics computation service;
the failover procedure is handled by ASAP cookies.
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3. Security considerations
The protocols used in the Reliable Server Pooling architecture only
try to increase the availability of the servers in the network.
RSerPool protocols do not contain any protocol mechanisms which are
directly related to user message authentication, integrity and
confidentiality functions. For such features, it depends on the
IPSEC protocols or on Transport Layer Security (TLS) protocols for
its own security and on the architecture and/or security features of
its user protocols.
The RSerPool architecture allows the use of different transport
protocols for its application and control data exchange. These
transport protocols may have mechanisms for reducing the risk of
blind denial-of-service attacks and/or masquerade attacks. If such
measures are required by the applications, then it is advised to
check the SCTP applicability statement RFC3257 [7] for guidance on
this issue.
4. Normative References
[1] Dreibholz, T., "Thomas Dreibholz's RSerPool Page",
URL: http://tdrwww.exp-math.uni-essen.de/dreibholz/rserpool/.
[2] Dreibholz, T., "An efficient approach for state sharing in
server pools", Proceedings of the 27th IEEE Local Computer
Networks Conference, October 2002.
[3] Dreibholz, T., Rathgeb, E., and M. Tuexen, "Load Distribution
Performance of the Reliable Server Pooling Framework",
Proceedings of the 4th IEEE International Conference on
Networking, April 2005.
[4] Dreibholz, T. and E. Rathgeb, "An Application Demonstration of
the Reliable Server Pooling Framework", Proceedings of the 24th
IEEE Infocom, March 2005.
[5] Dreibholz, T. and E. Rathgeb, "Implementing of the Reliable
Server Pooling Framework", Proceedings of the 8th IEEE
International Conference on Telecommunications, June 2005.
[6] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V.
Paxson, "Stream Control Transmission Protocol", RFC 2960,
October 2000.
[7] Coene, L., "Stream Control Transmission Protocol Applicability
Statement", RFC 3257, April 2002.
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[8] Tuexen, M., Xie, Q., Stewart, R., Shore, M., Loughney, J., and
A. Silverton, "Architecture for Reliable Server Pooling",
draft-ietf-rserpool-arch-09 (work in progress), February 2005.
[9] Stewart, R., Xie, Q., Stillman, M., and M. Tuexen, "Aggregate
Server Access Protocol (ASAP)", draft-ietf-rserpool-asap-11
(work in progress), February 2005.
[10] Xie, Q., Stewart, R., Stillman, M., and M. Tuexen, "Enpoint
Handlespace Redundancy Protocol (ENRP)",
draft-ietf-rserpool-enrp-11 (work in progress), February 2005.
[11] Stewart, R., Xie, Q., Stillman, M., and M. Tuexen, "Aggregate
Server Access Protocol (ASAP) and Endpoint Name Resolution
(ENRP) Parameters", draft-ietf-rserpool-common-param-08 (work
in progress), February 2005.
[12] Tuexen, M. and T. Dreibholz, "Reliable Server Pooling
Policies", draft-ietf-rserpool-policies-01 (work in progress),
June 2005.
[13] Conrad, P. and P. Lei, "Services Provided By Reliable Server
Pooling", draft-ietf-rserpool-service-01 (work in progress),
June 2004.
[14] "SETI@home: Search for Extraterrestrial Intelligence at home",
URL: http://setiathome.ssl.berkeley.edu.
[15] Bradner, S., "Intellectual Property Rights in IETF Technology",
RFC 3668, February 2004.
Author's Address
Thomas Dreibholz
University of Duisburg-Essen, Institute for Experimental Mathematics
Ellernstrasse 29
45326 Essen, Nordrhein-Westfalen
Germany
Phone: +49-201-1837637
Fax: +49-201-1837673
Email: dreibh@exp-math.uni-essen.de
URI: http://www.exp-math.uni-essen.de/~dreibh/
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