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DEN -- Web Services Load Balancing Framework

DEN is a Web Services load balancing framework applicable for all XSUL-based Web services. It is based on WS-dispatcher by Aleksander Slominski and Alexandre di Costanzo. "WS-Dispatcher allows internal services to be safely exposed to Internet and allows clients that do not have endpoints to become true WS peers and supports intermittently connected clients that may be moving between networks." DEN extends WS-Dispatcher in the following aspects:

  • Pipelining. DEN allows a Web service being disintegrated into multiple steps which are processed in a distributed way in Grids. For example, for a XPOLA-enabled Web services, we may divide it into 3 steps: 1. digital signature processing, 2. capability processing, and 3. service logic. Each step is to be attached with a DEN handler at the bottom of its handler stack, which will forward the processed SOAP message to the next processing node.
  • One-to-m mapping. Naturally for load balancing purpose, DEN maps one endpoint to one of m options specified in configuration with pluggable scheduling algorithms.
  • Supports HTTPS. If the endpoint of a Web service begins with "https" in configuration, DEN will automatically switch to HTTPS mode.
  • Hot-pluggable configuration. DEN-enabled services automatically reload configuration in every specified period of time; and thus we can change the processing routes on the fly.

A paper has been submitted on DEN.

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XPOLA has been integrated into XSUL as a component, please download it from CVS.

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Last updated: 16 Jul 2005
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