Self-organizing Replica Placement - A Case Study on Emergence

The concept of self-organization is rapidly gaining importance in the area of distributed computing system However, we still lack the necessary means for engineering such system in a standardized way since their common properties are rather abstract, and the mechanisms from which self-organization emerges are too diverse. Therefore,it has become common practice to engineer computing systems by taking inspirations from well-known case studies of biological systems. However, the concepts found in such systems are in many cases only partially transferable to the domain of distributed computing systems since biological systems are subject to vastly different constraints compared to those in a computing system. Our contributions in this paper are the following: (i) We present a case study of a self-organizing software system that originates from the domain of distributed computing systems. Therefore, its concepts can be exploited in other distributed computing systems much more directly, (ii) We give a detailed analysis of the emergent properties of the system and the mechanisms by which they arise, (iii) We generalize the mechanisms by which self-organization emerges in this system and present a catalog of design questions that may help engineers in creating arbitrary self-organizing systems.