Modeling And Analyzing Of Autonomic Dependability For Distributed Mission-Critical Systems

The special application of distributed mission-critical system raises higher demands for dependability. However, as the increasing deterioration of the network environment, the occurrence of various of Threats to Dependability(TtD), such as attacks, error and accidents is inevitable, which leads to deviations from the mission, operation interrupted, software failure, collapse of the crash, or even compromised or personal/property damages. Thus the TtD of distributed mission-critical system becomes increasingly serious. At the same time, the advancements in parallel computing, ubiquitous computing and mobile technology bring larger system scales, more complex architectures and growing diversity of targets, therefore the system management complexity has also become a great challenge. However, the traditional methods usually greatly increase the complexity of systems while improving dependability, thus they are not adaptable to the new situation and an new fine-grained approach of improving dependability for distributed mission-critical system is in great needs. In this case, for the characteristic of "technology ruled by technology", Autonomic Computing (AC) has the capability of self-management and its features of self-healing and self-protection contain dependability characteristics, so autonomic computing has been thought to be a new method to realize dependability and autonomic dependability is brought to public attention. But nowadays, the researches about autonomic dependability are still in their early stages, and most of autonomic dependability applications are rule-based, lacking of autonomic dependability model, specially a formal one. The status causes it hard to analyze the impacts from the key parameters in a global perspective, and hinders further developments.For the current problem of autonomic dependability, firstly a formal model of autonomic dependability for distributed mission-critical system is proposed in this paper, which can response to TtD in different levels and provide a theory basement for further study. On this basis, the core features of autonomic dependability, that is, self-reflection, self-healing and self-destruction are separately studied to analyze key factors to autonomic dependability, which can be used for refining and improving the model. The main contents are organized as follows. Firstly, a formal model of autonomic dependability for distributed mission-critical system is proposed based on SM-PEPA(Semi-Markov Performance Evaluation Algebra). The concepts and core features are studied at the beginning. And then an autonomic dependability model for distributed mission-critical system is built, in which the approaches of self-tolerance, self-healing and self-destruction are used to response to TtD in different levels under control of self-reflection. Furthermore, the model proposed is described by a formal language, SM-PEPA, which allows a rate of action following a general distribution. Based on this, a qualification method of autonomic computing is presented from a steady-state probability perspective, and autonomic dependability index is used as a metric to analyze the impacts of parameters on autonomic dependability. The autonomic dependability model is the base for subsequent chapters.Secondly, a layered self-reflection method for distributed mission-critical system is proposed. Accounting for existing research results of autonomic computing, the Autonomic Feedback Control loop(AFC) is designed, and the components are modified to be autonomic by adding the AFCs. Then we combine the context -awareness and self-awareness to set up a two-layered self-reflection architecture. In the architecture, the local self-reflection is helpful to decrease the cost of Autonomic Element(AE) in the self-reflection process, and the global self-reflection acts as a safeguard for the consistency of all parts. Due to the shortcoming of current model based on natural language or graph,Ï€-calculus is used to describe the self-reflection architecture formally from higher and abstract level, reducing vulnerabilities. The self-reflection mechanism provides a precondition of self-management for self-healing and destruction in chapter 3 and 4.Thirdly, an analysis method of self-healing for distributed mission-critical system is proposed based on fluid-flow approximation of PEPA. According to the complexity of analyzing self-healing, a new analysis method of self-healing is built on the use of fluid-flow approximation of PEPA after studying requirements and representative architectures of self-healing for distributed mission-critical systems. In the method, we consider the process of self-reflection as well as the addition and deletion of components. Then PEPA could be converted to Ordinary Differential Equations (ODEs) to avoid state-space explosion confronted by Markov process currently. The experimental results show that comparing to traditional state-based methods, our work is with a good result by limiting the solution time in linear time, when there are a large number of component in the process of self-healing.Lastly, a self-destruction method for distributed mission-critical system inspired by apoptosis is proposed. According to the process of apoptosis in biological systems, a self-destruction structure in a combination of active and passive mode is designed for the software destruction of distributed mission-critical system on the basis of self-reflection. Based on this, MRSPN(Markov Regeneration Stochastic Petri Net) is used to modeling the process of self-destruction to provide a qualification analysis approach. This self-destruction method can be widely used as an ultra protection way for autonomic dependability. After analyzing the key parameters in the MRSPN model, simulation experiments prove that decreasing the failure of heartbeat and time used for destruction can improve the autonomic dependability.