Design Patterns in Peer-to-Peer Systems A Pattern Language for Overlay Networks

Developing peer-to-peer systems is a big challenge, because they typically operate in large-scale, highly unreliable and insecure environments and involve the collaboration of many nodes (i.e. computers) in the network. In recent times, a lot of efforts have been devoted to the system design of peer-to-peer systems, resulting in new structured overlay networks. These overlay networks perform the routing task needed to localize items in the network efficiently even in the presence of node failures and attacks. However, to tackle the full complexity of practical peer-to-peer systems, also good software design needs to be applied. Yet, lots of peer-to-peer systems are developed in an ad-hoc manner, and little has been written about their software architecture. In this semester project, I have tried to analyze the software design of overlay networks, the common abstraction of most peer-to-peer systems. Design patterns have been very successful in documenting proven and reusable solutions; consequently, I have tried to discover design patterns for overlay networks by investigating different academic and open source projects, and applying and improving them on a real-world system. This paper presents the result of this work: a pattern language for overlay networks, consisting of a number of patterns and their relationships, trying to cover most aspects of overlay networks. For that reason, most patterns are also not new, but are simply adaptations of well-known patterns to the specific requirements of overlay networks. The remaining patterns can be regarded as suggested proto-patterns.