Maintaining Consistency in Reconfigurable Aspect- Oriented Middleware Bholanathsingh Surajbali, Geoff Coulson and Paul Grace Computing Department, Lancaster University Lancaster, UK {b.surajbali, geoff, p.grace} @comp.lancs.ac.uk Abstract. Aspect-oriented middleware is a promising technology for the realisation of dynamic reconfiguration in heterogeneous distributed systems. However, like other dynamic reconfiguration approaches, AO-middleware- based reconfiguration requires that the consistency of the system is maintained across reconfigurations. AO-middleware-based reconfiguration is an ongoing research topic and several consistency approaches have been proposed. However, most of these approaches tend to be targeted at specific narrow contexts, whereas for heterogeneous distributed systems it is crucial to cover a wide range of operating conditions. In this paper we propose an approach that offers distributed dynamic reconfiguration in a consistent manner, and features a flexible framework-based consistency management approach to cover a wide range of operating conditions. We evaluate our approach by investigating the flexibility, configurability and transparency of our approach and also quantify the performance overheads of our framework. Keywords: AO-middleware, dynamic reconfiguration, consistency, flexibility, configurability, transparency. 1 Introduction A key and growing challenge for distributed systems is their need to support dynamic reconfiguration in order to maintain optimal levels of service in diverse and changing environments. In response to this challenge, aspect-oriented middleware (AOM) has recently emerged as a promising basis on which to build reconfigurable distributed systems [19, 22]. The core concept of AOM systems is that of an aspect: a software module that deals with one specific concern, and which can be changed independently of other modules. Aspects are also associated with compositional logic (often called a pointcut) that describes declaratively where and when the aspect should be composed. The attraction of AOM based reconfiguration lies in the fact that aspects are inherently orthogonal encapsulations of behaviour and pointcuts are inherently location independent. Maintaining consistency is a fundamental requirement in the evolution of all dynamically reconfigurable distributed systems, including AOM systems: dynamic