David Granflo MSE-2004-32, pp. 25. TEK/avd. för programvaruteknik, 2004.
Architectural design decisions are known to be crucial for the success of a system in development. An early design decision will most likely be expensive to change at a later stage of the development if the software engineers needs to get back to the drawing board. If a quality attribute has been neglected during architectural design it may ruin the entire project. This work describes a way of increasing the availability of a software service, that have already been put into use, by adding a middle layer of replication logics represented by third party application servers and replicated Enterprise JavaBeans. The approach called Three-tier replication is assessed and compared to the origin architectural design by using a qualitative scenario based assessment. In addition, we have also implemented the new architectural design to be able to validate the assessment results. The validation is done by testing the scenarios on the two architectures. The software service used is an industrial system for sending text messages from computers to mobile phones.