Architectural design for resilience

This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, redistribution , reselling , loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Resilience has become a new nonfunctional requirement for information systems. Many design decisions have to be made at the architectural level in order to deliver an information system with the resilience property. This paper discusses the relationships between resilience and other architectural properties such as scalability, reliability, and consistency. A corollary is derived from the CAP theorem, and states that it is impossible for a system to have all three properties of consistency, resilience and partition-tolerance. We present seven architectural constraints for resilience. The constraints are elicited from good architectural practices for developing reliable and fault-tolerant systems and the state-of-the-art technologies in distributed computing. These constraints provide a comprehensive reference for architectural design towards resilience. 1. Introduction The term 'resilience' was originally used to describe the property of a material that can absorb external energy when it is forced to deform elastically, and then be able to recover to its original form and release the energy. When 'resilience' is used for complex systems in the context of ecology, it refers to 'the capacity of a system to absorb disturbance and reorganise while undergoing change so as to still retain essentially the same function, structure, identity, and feedbacks' (Walker et al. 2004). For information systems, resilience refers to a system's capability to 'provide and maintain an acceptable level of service in the face of various faults and challenges to normal operation'. 1 Besides that, it also implies a system's capability to recover to normal operational state with all available resources (Ahmed and Hussain 2007). In this paper, resilience refers to the capability of an information system that sustains the same function with little degraded service level under unexpected workload or disturbance that can cause partial failures …