HIGH AVAILABILITY AND SOFTWARE ARCHITECTURE

Abstract

<p>As one of the main objectives of Enterprise Business Applications, high availability is becoming more and more important and is a widespread concern of customers, architects and developers. But, until now there are still no models for computing and evaluating accurately the value of a system's availability, and no any feasible and systematic methods to improve the availability 'of a software system, which may be made up of several patterns, and may be very complex. PBSA(Part Based Software Architecture), as a new analytical model for predicting a complex software system's availability, is based on the availability of each component, the properties of some main architecture patterns, and the architectural structure of the software system itself. It uses a Markov model to translate the evaluation process of a system's availability into a Markov Transfer process, and uses the properties of Markov Chains to calculate and predict the probability of the whole system's availability. Then based on the model, a sensitivity rank for architecture components and factors can be given, and systematic strategies for improving the availability property of a complex application system can be given. As one of the strategies for improving system availability, a new component, named the HA(high availability) manager component, is defined and introduced, together with some idea of an HA Hierarchy.</p>