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Case Study: Loadbalancing whitin the Amazon Cloud

Initial Situation

Duden provides Internet-based correction solutions at www.duden.de. The corrections are performed by multiple instances of the Duden Enterprise Servers that run at the Amazon cloud. So far loadbalancing occurred at the level of the HTTP protocol, which distributed the load onto individual nodes. A scaling of the server farm was responsible for the launch of additional nodes during heavy load or for the shutdown of nodes in times of decreasing usage.
The existing loadbalancing did not support sessions based on Web Services. However, sticky sessions using the SOAP protocol were necessary to run more applications at the server farm.


To run all applications within the cloud a loadbalancing solution was needed that would meet the following requirements:

Membrane Service Proxy

When searching for a suitable loadbalancer among others the Membrane Service Proxy was investigated. At that time Membrane did not support SOAP sessions, but Membrane was easily extensible by Java and the source code was freely available.


The decision was made in favor of an extension for SOAP-based sessions for Membrane Service Proxy. To implement the extension an open source sponsorship contract was signed with predic8, the manufacturer of Membrane Service Proxy. The implemented functions for Duden were published under the ASF open source license and thus are available to the general public. Duden benefits from bug fixes and the experience of other users. Since the extension was integrated into the Membrane distribution, Duden can upgrade to new Membrane versions without performing a migration project.
The extension consists of the following components:


"Due to the extensibility of Membrane, we were able to implement the load balancing exactly as required. Since over a year Membrane Service Proxy is working fast and reliably. The machine running the software is barely on load. We would do it with Membrane Service Proxy any time again."

Heinz-Detlev Koch, Speech Technology Development at Duden

About Duden

As an authority Duden observes permanent changes to the German language. In addition to that Duden provides a range of products to ensure that the current set of rules are available to anyone at any time. The products comprise solutions and applications for the flawless professional written communication based on the Duden language technology. While private customers mostly benefit from the Duden spellchecker in their office applications, Duden Business Solutions provides customized cross-industry solutions that are adapted to quality assurance and can be equipped with custom enhancements.
Every digital correction tool by Duden accesses the most comprehensive and most recent editorially administrated vocabulary of the German language and can be flexibly integrated into existing processes and software solutions. Since 2001 these solutions are sold on the market and are market-leading. Duden-correction software is available as single user version, network solution and as an integral component in Office programs and systems for typesetting, editing and translation. The business and private products are used by millions of users.
More information can be found online at www.duden-business-solutions.de.