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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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.¶
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 [6].¶
The application scenario for Distributed Computing is defined as follows:¶
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 [21], it is
not possible to let clients fetch a job, process it later and may be
some day upload the result.¶
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.¶
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.¶
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.¶
Maintaining a Distributed Computing pool for the scenario described above
arises the following requirements to the pool management:¶
It must be possible to manage large server pools, e.g. up to some hundreds
or even thousands of servers.¶
Due to heterogeneous processing resources within a pool, it
must be possible to use appropriate server selection procedures to
meaningfully utilize the available resources.¶
It must be possible to dynamically add and remove servers.¶
Servers may be unreliable, especially when the servers are represented by
user PCs. Failover mechanisms are required to continue an interrupted
computation session.¶
All requirements for pool and session management of the Distributed Computing
scenario defined in the previous section can be fulfilled by the Reliable
Server Pooling architecture:¶
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
[15], [12].¶
RSerPool allows to specify server selection rules by pool member selection
policies [8]. A set of adaptive and
non-adaptive 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
[12],
[14],
[18],
[19],
[13]
for details.¶
Dynamic addition and removal of PEs is a feature of RSerPool
[4].¶
The control/data channel concept
[3] 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 [14], [17]
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
[22] using the RSerPool session layer in a
Distributed Computing application is described in
[16].¶
Applying RSerPool for distributed computing applications, the duties of the
RSerPool architecture are still limited to the management of pools and
independent sessions only. It is in particular a non-goal to provide
functionalities like data synchronization among sessions, user
authentication, accounting or the support for more than
one administrative domain. Such functionalities are considered to be
application-specific and are therefore out of the scope of RSerPool.¶
The RSerPool reference implementation RSPLIB,
including example Distributed Computing applications,
can be found at
[22]. It supports the functionalities
defined by
[3],
[4],
[5],
[6] and
[7] as well as the options
[9],
[11] and
[10].
An introduction to this implementation is provided in
[12].¶
A large-scale and realistic Internet testbed platform with support for the multi-homing feature of the underlying SCTP protocol is NorNet. A description of NorNet is provided in [20], some further information can be found on the project website [23].¶
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 (see [2]) applicability statement
[1] for guidance on this issue.¶
Lei, P., Ong, L., Tuexen, M., and T. Dreibholz, "An Overview of Reliable Server Pooling Protocols", RFC 5351, DOI 10.17487/RFC5351, , <https://www.rfc-editor.org/info/rfc5351>.
[4]
Stewart, R., Xie, Q., Stillman, M., and M. Tuexen, "Aggregate Server Access Protocol (ASAP)", RFC 5352, DOI 10.17487/RFC5352, , <https://www.rfc-editor.org/info/rfc5352>.
[5]
Xie, Q., Stewart, R., Stillman, M., Tuexen, M., and A. Silverton, "Endpoint Handlespace Redundancy Protocol (ENRP)", RFC 5353, DOI 10.17487/RFC5353, , <https://www.rfc-editor.org/info/rfc5353>.
[6]
Stewart, R., Xie, Q., Stillman, M., and M. Tuexen, "Aggregate Server Access Protocol (ASAP) and Endpoint Handlespace Redundancy Protocol (ENRP) Parameters", RFC 5354, DOI 10.17487/RFC5354, , <https://www.rfc-editor.org/info/rfc5354>.
[7]
Stillman, M., Ed., Gopal, R., Guttman, E., Sengodan, S., and M. Holdrege, "Threats Introduced by Reliable Server Pooling (RSerPool) and Requirements for Security in Response to Threats", RFC 5355, DOI 10.17487/RFC5355, , <https://www.rfc-editor.org/info/rfc5355>.
Dreibholz, T. and X. Zhou, "Definition of a Delay Measurement Infrastructure and Delay-Sensitive Least-Used Policy for Reliable Server Pooling", Work in Progress, Internet-Draft, draft-dreibholz-rserpool-delay-28, , <https://www.ietf.org/archive/id/draft-dreibholz-rserpool-delay-28.txt>.
Dreibholz, T., Zhou, X., and E. P. Rathgeb, "A Performance Evaluation of RSerPool Server Selection Policies in Varying Heterogeneous Capacity Scenarios", Proceedings of the 33rd IEEE EuroMirco Conference on Software Engineering and Advanced Applications Pages 157-164, ISBN 0-7695-2977-1, DOI 10.1109/EUROMICRO.2007.9, , <https://www.wiwi.uni-due.de/fileadmin/fileupload/I-TDR/ReliableServer/Publications/EuroMicro2007.pdf>.
Dreibholz, T. and E. G. Gran, "Design and Implementation of the NorNet Core Research Testbed for Multi-Homed Systems", Proceedings of the 3nd International Workshop on Protocols and Applications with Multi-Homing Support (PAMS) Pages 1094-1100, ISBN 978-0-7695-4952-1, DOI 10.1109/WAINA.2013.71, , <https://www.simula.no/file/threfereedinproceedingsreference2012-12-207643198512pdf/download>.