Dependable distributed systems

Distributed software systems are the basis for many innovative applications. The key for achieving scalable and maintainable distributed systems is dependability, because otherwise the complexity of distribution would leave the system uncontrollable. Hence, our approach aims at a concept for optimizing dependability. Similar to other approaches we use replication as means to provide transparent fault-tolerance and persistence, but we especially focus on increasing availability by relaxing data integrity by using a mixture of asynchronous and synchronous replication techniques. This work contributes three main aspects: First, a description of the envisioned trade-off between availability and consistency, secondly with a mechanism to achieve this trade-off, and thirdly, with models that use this mechanism and can be transparently deployed by developers. This work aims at enabling a configurable and application-specific optimum of availability, possibly even controlled during runtime. A real-life telecommunication application serves as proof of concept.