An aspect-oriented middleware architecture supporting consistent dynamic reconfiguration

Abstract

Distributed systems are increasingly being deployed in environments that range from small and tightly-coupled, such as wireless sensor networks, to large and loosely coupled, such as telecommunication systems. Middleware has emerged as a key technology in the construction of such systems, but middleware is increasingly required to be highly modular and configurable, to support separation of concerns between services, and, crucially, to support dynamic reconfiguration: i.e. to be capable of being changed while running. The goal of this thesis is to investigate, design and evaluate a novel approach to middleware-based dynamic reconfiguration that is based on the Aspect Orientation (AO) paradigm. In particular, the thesis proposes an aspect-oriented middleware platform called AO-OpenCom that builds AO-based reconfiguration on top of a dynamic component approach to middleware system composition. The goal is to support extremely flexible dynamic reconfiguration that can be applied both vertically and horizontally: i.e. at all levels of the system and uniformly across the distributed environment. The thesis also proposes a framework-based approach that supports consistent distributed dynamic reconfiguration to avoid problems that arise when reconfiguration operations are, for example, initiated concurrently or in the face of unstable infrastructure or involving contradictory compositions. The approach here is to define a model of potential threats to consistency and to introduce so-called 'threat aspects' that can be dynamically composed with the middleware platform to guard specifically against particular threats. Using dynamically-composed aspects both to realise dynamic reconfiguration and to guard against inconsistency lends simplicity and uniformity to the middleware. Furthermore, the design is recursive in that threat aspects can themselves be protected against other threats using the same approach. For example, a threat aspect addressing a security threat might be protected from security infrastructure crashes by being composed with a threat aspect that offers server replication. Inevitably, the ability to support dynamic reconfiguration and overcome reconfiguration inconsistency comes at the cost of an incurred performance overhead; hence; the thesis also investigates the impact of these overheads.EThOS - Electronic Theses Online ServiceGBUnited Kingdo