A Fault Model Centered Modeling Framework for Self-healing Computing Systems

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1 A Fault Model Centered Modeling Framework or Sel-healing Computing Systems Wei Lu 1, Yian Zhu 1, Chunyan Ma 1, and Longmei Zhang 2 1 Department o Sotware and Microelectronics, Northwestern Polytechnical University, Xi an, , China 2 Department o Electronics Inormation, Northwestern Polytechnical University, Xi an, , China {luweinpu,zhuya,machunyan}@nwpu.edu.cn, longmei.zhang@gmail.com Abstract. As the computing systems become more and more complex, new technology and approach are desired to construct the system, so as to make them more reliable or sel-healable. A modeling ramework to generating selhealing system is proposed in this paper. The model ramework consists o unction model, ault model, sel-healing model, model composition mechanism or integration o the unction model and the sel-healing model, as well as a code generation platorm that supports automated generation o sel-healing enabled sotware systems. The ramework has the advantages o the ollowing aspects: 1) The unctional s o target system and the sel-healing s or the target system can be modeled respectively under the ramework; 2) The unctional models and the sel-healing models can be coupled through ault model; 3) The sel-healability o the target system can be analyzed at he model level; 4) The modeling ramework is platormindependent. Keywords: computing systems, model, sel-healing, ramework. 1 Introduction Large scale computing and inormation systems are a vital and integral part o today s society. Many modern IT systems are to such a degree critical or essential inrastructure, and sometimes or human lie, that no downtime is actually acceptable. As the development o computer and network, typical present-day computing systems are more and more complex so that they are becoming increasingly diicult to execute robustly. Computing systems have reached a level o complexity where the human eort required to get the systems up and running and keeping them operational is getting out o hand. When computer systems operate abnormally, detecting and resolving the problem requires much time and eort, even some time it is impossible. An increasingly signiicant requisite or computing systems is the ability to handle resource variability, ever-changing user needs and system aults. This new requisite poses new challenges or computing systems designers and developers. Sel-healing approach attempt to enable computing systems to automatically discover, diagnose, H. Deng et al. (Eds.): AICI 2011, Part II, LNAI 7003, pp , Springer-Verlag Berlin Heidelberg 2011

2 62 W. Lu et al. and repair (or at least mitigate) aults without human intervention, thus it is a potential approach to resolve the problem. In recent years, research o sel-healing has been given a considerable attention to construct target system reliable. Several approaches have been proposed to develop sel-healing system, including -based, Architecture-based, and log-based approaches. These approaches have been used to developed sotware systems so as to make the systems more reliable or sel-healable or some aults. As more and more researchers and engineers attempt to use sel-healing approaches to develop computing systems in area such as deep-space exploring and environment monitoring where manual repairing is not easible or diicult when anomalies occur, how to model a sel-healing system and how to evaluate the sel-healability o the system we have constructed become the important issues need to be resolved. This paper proposed a modeling ramework to generating the ability o selhealing. This remainder o the paper is organized as ollows: Section 2 is devoted to an in-depth analysis o related works. Section 3 describes requirements or selhealing system. In Section 4, we describe our modeling ramework or sel-healing system. Finally, Section 5 presents our conclusions and uture works. 2 Related Works Currently, the architecture o sel-healing systems and the technologies or implementing a sel-healing system have been researched rom diverse views and some engineers have been trying to make use o the sel-healing mechanism to resolve special problems they encountered in various ield [1]. Jerey O.Kephart et. al. view sel-healing as the most important characteristic o an autonomic computing system. They depict the process o sel-healing as the system to detect, diagnose, and repair localized problems resulting rom bugs or ailures in sotware and hardware[2]. To achieve autonomic computing, they has suggested a reerence model which sometime called the MAPE-K(Monitor, Analyze, Plan, Execute, Knowledge) model[3]. This model is being reerenced by more and more researchers to achieve a sel-healing system. SHADOWS (Sel-healing Approach to Designing Complex Sotware Systems)[4] was a three-year EU IST STREP project started in Jun 2006 which aimed at developing technologies that augment large sotware systems with a sort o immune response against contingencies that can occur at design-time or runtime. The project proposes an automatic or semi-automatic detection and repair o possibly problematic behavior in its early design and development stages[5]. Emil Vassev proposed an Autonomic System Speciication Language (ASSL) or describing autonomic systems[6]. The Autonomic System Speciication Language (ASSL) is a declarative speciication language or autonomic system with well deined semantics including modern programming language concepts and constructs like inheritance, modularity, type system and high abstract expressiveness. This language addresses the problem o ormal speciication and code generation o autonomic systems within a ramework. Emil Vassev presented concrete results on the use o ASSL to speciy a sel-healing behavior model or NASA swarm-based exploration missions and to generate an application skeleton o the same.

3 A Fault Model Centered Modeling Framework or Sel-healing Computing Systems 63 Other researchers devote to design sel-healing mechanisms or speciic issues in their respective areas and implement speciic systems with sel-healing characteristics. Most o the current researches in sel-healing areas are directed at the system architecture and implementing technologies or speciic sel-healing mechanisms. But or a general system, how to model it so as to make the system with some sel-healing characteristics and how to evaluate the sel-healability o the system are two important problems reserved to be resolved. 3 Requirements or Sel-healing Systems At present, there is not an accurate or strict deinition that is consensus-based or selhealing system or or sel-healability o a system. Most o the depictions about selhealing system or sel-healability appeared in relative literatures and reports are conceptive and qualitative. Ghosh et al deine sel-healing as the property that enables a system to perceive that it is not operating correctly and, without (or with) human intervention, make the necessary adjustments to restore itsel to normalcy[1]. Huebscher et. al. view selhealing as a property o an autonomic computing system and depict it as the capability o a system to detect, diagnose problems and to ix the problems i possible[7]. Gorla et. al. indicate that designing or sel-healing should aim to make the system support our main phases as ailure prediction or detection, ault diagnosis or localization, ault isolation or ailure recovery, and validation[8]. Furthermore, they proposed some guidelines or enhancing sel-healing capabilities o sotware systems during the design phase. Laster et. al. think that Sel-Healing denotes the system ability to examine ind, diagnose and react to system malunctions. They describe the process o sel-healing as a closed loop cycle composed o our stages which are monitoring, error detecting and diagnosing, error analyzing and repair operation selecting, repair operation executing[9]. According to literatures and reports delivered in public, or a system to be selhealing, it must be able to detect the aults occurrences, identiy their causes, diagnose or localize the aults, isolate or repair the aults, and validate the repairs. We can divide the process o sel-healing into two phases mainly. The irst phase is the aults detection. The second phase is the system response. Dierent views have been proposed about respective tasks in every phase. We think that system monitor and aults diagnose should be the main tasks in aults detection phase and aults repair should be the main task in system response phase. But there is no a consensus-based view about the method and process or aults repair up to the present. Through the discussion about the requirements or sel-healing above, we can summarize that a sel-healing system should be composed o two parts which are unction part and sel-healing part. The unction part comprise unction s which realize the system s unctional requirements and the sel-healing part comprise sel-healing s which ulill the sel-healing process such as monitoring, diagnosing and repairing etc. So the structure o sel-healing system can be depicted as an integrator composed o the unction s and the sel-healing s. We can illustrate the structure o sel-healing system using igure 1.

4 64 W. Lu et al. Eector Eector Monitor Diagnosor Eector Repairor Eector Fig. 1. The structure o sel-healing system In igure 1, the unction part and the sel-healing part are weaved tightly together through sensors and eectors. s, oten called probes or gauges, collect inormation about the unction and the environment in which the unction run. Eectors carry out changes to the unction. According to the structure o sel-healing system in igure 1, two problems should be resolved beore we can achieve a sel-healing system. The irst problem we should encounter in system design phase is how to model the system especially the selhealing part so that make it with sel-healing characteristics. The second problem we should encounter in system implementation phase is how to manage the degree o coupling between the unction s and the sel-healing s. The problem about how to manage the degree o coupling between unction s and sel-healing s is out o this paper. We will discuss the irst problem primarily in remainder o this paper. 4 The Modeling Framework I we want to model or implement a sel-healing system directly based on its structure depicted in igure 1, we will soon all into chaos because we have to consider the selhealing part when we ocus on the unction part. How many sensors and eectors will be needed and where to deploy them are all problems that we should resolve beore we can implement the sel-healing part. All the issues about sel-healing part will distract us rom designing unction part so we will soon ind that the system are becoming more and more complex as more and more sel-healing s tangled with the unction s. Even we implement the system inally through our iterative hard work, how to evaluate the sel-healability or sel-healing degree o the system will be a crucial problem we have to consider. We think that the unction part and the sel-healing part o the system should be modeled respectively. When the model o sel-healing part was separated rom the unction model, the sensors and eectors will be removed rom the unction model so we can ix our attention on the unction part. But when we inish the unction model, how to set the sensors and eectors and redeploy them to the system or in other words how to joint the sel-healing model to the unction model so as to provide the system

5 A Fault Model Centered Modeling Framework or Sel-healing Computing Systems 65 with some sel-healing characteristic will be the key problem should be resolved. We propose a modeling ramework to resolve the problem so as to acilitate the development o sel-healing sotware systems. A ault model was used as the ligaments in our ramework to keep the associations between the unction model and the sel-healing model. In literature [10], we indicated that the sel-healability o a computing system should be relative to the ault model o the system. We view the deinition o selhealability o a computing system we proposed in literature [10] as the theoretical basis or the modeling ramework. The ramework consists o a unction model, a ault model, a sel-healing model, a model composition mechanism or integration o the unction model and the selhealing model, as well as a code generation platorm that supports automated generation o sel-healing enabled sotware systems. Figure 2 illustrates a conceptual architecture o the ramework. Fault Model Monitor Diagnosor model Model composition Eector Repairor Eector Healing policy Sel-healing model Code generation Sel-healing sotware system Code generation Program composition Fig. 2. Sel-healing system modeling ramework The aim o this ramework is to integrate various existing sotware techniques with Model Driven Architecture (MDA) approaches, with the intent to provide a united platorm to enable sel-healing sotware systems to be engineered and implemented rom model speciications. Many technologies, methods and support tools have been proposed or unction modeling so we will only discuss the other part in the ramework. 4.1 Fault Model We deine the basic ault noted as symbol as the minimal event unit that result in system abnormity. We note the set o all the possible basic aults as symbol Σ, so

6 66 W. Lu et al. Σ = { 1, 2, n}. We can divide the according to their types. We deine each subset o Σ to some mutually exclusive subsets Σ as a macro-ault noted as F. The macro-aults can also be classiied according to their types. We can go on the classiying until we achieve a tree structure about the aults. Figure 3 illustrates the tree structure o aults model. All lea nodes in the tree are basic aults and other nodes are macro-aults. Once we have constructed a tree structure o the system aults, the objective o sel-healing modeling is how to support the ault model that is how to diagnose and repair every ault in the aults model. Furthermore, we can analyze the sel-healability o the system ater the sel-healing model being inished through the aults model. We have discussed the relationship between sel-healability and aults model in literature[10]. F 0 F 11 F 13 1 F 0 F Fig. 3. The tree-based ault model 4.2 Sel-healing Model The sel-healing model or sotware system can be constructed based on the ault model. A sotware ault (basic ault or macro-ault) can be detected by the diagnostician through the inormation collected by one or more monitors and repaired by the repairer through one or more eectors. Similarly, preventive eectors can be taken when the occurrence o aults is predicted. The sel-healability o the system can by analyzed through the degree o the aults model supported by the sel-healing model. 4.3 Model Composition A sel-healing model is described as a set o abstract constructs that are instantiated when it is associated with the base system models. In this way, the sel-healing eature is kept separate rom the base unctionality o the sotware system. The decomposition o the base unctionality and the sel-healing eature improves modularity and re-usability o the sel-healing modules. The main advantage o this approach is that it allows developing and maintaining the sel-healing models independently rom the base model. Furthermore, sel-healing models can be applied to all levels in the sotware system hierarchy. Besides, according to dierent

7 A Fault Model Centered Modeling Framework or Sel-healing Computing Systems 67 requirements or systems to be sel-healing, we can construct dierent sel-healing models to support the ault model in dierent degrees. Deploying a sel-healing model to the unction model is done by model composition techniques. Typically, model composition involves merging two or more models to obtain a single integrated model. Aspect-Oriented Modeling is a promising research area that supports model composition. Sel-healing models can be speciied as crosscutting aspects that are embedded in the base models. Model weaving is another approach or model composition, wherein the relationships between the models are captured in a weaving model. A weaving model is one that speciies dierent kinds o mappings between model elements. By adopting this approach, a separate weaving model is created that explicitly speciies the links between base models and sel-healing models. All three kinds o models (i.e., base, sel-healing and weaving models) will be ed to a weaver engine and composed into a single integrated model. 4.4 Code Generation and Program Composition The sel-healing models are speciied in a platorm-independent manner. To support a complete sel-healing application, a amily o code generators needs to be employed or transorming platorm-independent models into platorm-speciic code, each describing how the sel-healing eatures are implemented on a dierent platorm. The base and sel-healing models are translated into platorm-speciic implementations by their own code generators, respectively. The base code is then augmented with the sel-healing instrumentation by using program composition techniques. As a result, a complete sel-healing enabled sotware system is constructed and directly mapped to the representation o the composed sel-healing enabled sotware model, upon which model-based analysis can be perormed or system veriication and validation. 5 Conclusions and Future Works In this paper we show a generic ramework or modeling sel-healing sotware systems. A tree-based ault model is used in the ramework to keep the association between unction model and sel-healing model o the system. We can model the selhealing part o the system based on the ault model so the unction part and the selhealing part o the system can be modeled respectively under the ramework. Furthermore, we can analyze the sel-healability o the system through how the selhealing model can support the ault model when we implement the system. The ramework can also be used to analyze the sel-healability o legacy systems. Under our modeling ramework, Sel-healing is achieved by transorming the sel-healing models into platorm-speciic implementation, which is then composed with the base module to orm an integrated sotware system that provides ailure resolutions to mitigate the eect o sotware aults. With the progress o AOM, we expect that the sel-healing code ramework can be build automatically through the sel-healing model.

8 68 W. Lu et al. There are still a ew open tasks that should be done. Currently we are ocusing on developing the method to modeling the system aults based on tree structure. Model composition is another important technology we are investigating all along. Acknowledgment. This work is partially supported by Aviation Science Fund #2010ZD53047 to Lu Wei. Reerences [1] Ghosh, D., Sharman, R., Raghav Rao, H., Upadhyaya, S.: Sel-healing systems survey and synthesis. Decision Support Systems 42, (2007) [2] Kephart, J.O., Chess, D.M.: The vision o autonomic computing. Computer 36, (2003) [3] IBM, An architectural blueprint or autonomic computing, IBM (2003) [4] Shehory, O.: SHADOWS: Sel-healing complex sotware systems. In: 23rd IEEE/ACM International Conerence on Automated Sotware Engineering - Workshops, ASE Workshops 2008, pp (2008) [5] Jung, G., Margaria, T., Wagner, C., Bakera, M.: Formalizing a Methodology or Designand Runtime Sel-Healing. In: 2010 Seventh IEEE International Conerence and Workshops on Engineering o Autonomic and Autonomous Systems (EASe), pp (2010) [6] Vassev, E., Paquet, J.: ASSL - Autonomic System Speciication Language. In: 31st IEEE Sotware Engineering Workshop, SEW 2007, pp (2007) [7] Huebscher, M.C., McCann, J.A.: A survey o autonomic computing degrees, models, and applications. ACM Comput. Surv. 40, 1 28 (2008) [8] Gorla, A.: Towards design or sel-healing. In: Fourth International Workshop on Sotware quality assurance: in conjunction with the 6th ESEC/FSE Joint Meeting, Dubrovnik, Croatia, pp (2007) [9] Laster, S.S., Olatunji, A.O.: Autonomic Computing: Towards a Sel-Healing System. In: Proceedings o the Spring 2007 American Society or Engineering Education Illinois- Indiana Section Conerence (2007) [10] Lu, W., Zhu, Y., Zhang, L.: Further exploring understanding o sel-healability o computing system using discrete-event model. Xibei Gongye Daxue Xuebao/Journal o Northwestern Polytechnical University 28, (2010)