Candy: Component-based Availability Modeling Framework for Cloud Service Management Using SysML Fumio Machida 1,2 , Ermeson Andrade 1,3 , Dong Seong Kim 1 and Kishor S. Trivedi 1 1 Department of Electrical and Computer Engineering, Duke University, Durham, NC 27708, United States fm50@duke.edu, ec130@duke.edu, dk76@duke.edu, kst@ee.duke.edu 2 Service Platforms Research Laboratories, NEC Corporation, Kawasaki, Japan f-machida@ab.jp.nec.com 3 Informatics Center, Federal University of Pernambuco (UFPE), Recife, PE, Brazil ecda@cin.ufpe.br Abstract— High-availability assurance of cloud service is a critical and challenging issue for cloud service providers. To quantify the availability of cloud services from both architectural and operational points of views, availability modeling and evaluation are essential. This paper presents a component-based availability modeling framework, named Candy, which constructs a comprehensive availability model semi-automatically from system specifications described by Systems Modeling Language (SysML). SysML diagrams are translated into components of availability model and the components are assembled together to form the entire availability model in Stochastic Reward Nets (SRNs). In order to incorporate the maintenance operations of cloud services in availability models, Candy defines the translation rules from Activity diagram to SRN and synchronizes the related SRNs according to SysML allocation notations. The feasibility of the proposed modeling and availability evaluation process is studied by an illustrative example of a web application service hosted on a cloud infrastructure having multiple failure- isolation zones and automatic scale-up function. Keywords-component; automatic scale-up, availability assessment, cloud service, stochastic reward nets (SRNs), systems modeling language (SysML) I. INTRODUCTION Cloud computing is an emerging style of computing service to provide shared computing resources on the Internet or private networks on an on-demand basis. Cloud service providers own service infrastructures and take responsibility for infrastructure management. The users of cloud services do not need to own service infrastructures and can save the costs related to infrastructure management. As cloud services have been used widely, the availability of cloud services becomes a major concern of the users. Cloud services occasionally become unavailable due to system failure or scheduled maintenance. The users, however, cannot control the downtime of the service because most of the maintenance operations and recovery processes are delegated to the cloud service provider. Cloud service providers should assess the availability of their service quantitatively and disclose the information to the users. To analyze the availability of cloud services based on their system configurations and maintenance operations, model-based availability assessment provides a reasonable solution. Analytic models such as Markov chains and stochastic Petri nets are used to analyze the availability of complex IT systems [1][2]. However, a comprehensive availability model for a complex IT system cannot be easily obtained without expertise in analytic modeling. Cloud service infrastructures have complex configurations and the states of the systems are dynamically changing. Although such complex configurations and dynamic behavior are understood well by system administrators who are responsible for maintaining cloud service infrastructures, it is not easy for them to compose a comprehensive availability model from scratch. If availability model can be generated from the knowledge of system administrators through a well- defined procedure, it becomes very useful in assessing the availability of the cloud services. This paper presents a component-based availability modeling framework named Candy, to compose an availability model for cloud service semi-automatically from the system specification model expressed in Systems Modeling Language (SysML) [3]. SysML is defined as an extension of Unified Modeling Language (UML) [4] and is used for modeling complex IT systems and various system engineering applications. Candy translates the SysML diagrams into the components of an availability model. These components are then assembled and synchronized together according to the dependencies among them in order to form an entire availability model as stochastic reward nets (SRNs) [5]. The model translation has been studied in previous literature [6][7][8][9]. Most of the existing model translation methods aimed to evaluate the performance of the system [6][7]. A few studies addressed the availability assessment [8][9], but they did not incorporate maintenance operations which do affect the system availability. In contrast to the existing studies, the key contributions of our work can be summarized as follows. i) SRNs are composed for the purpose of availability analysis of complex IT systems. ii) Dynamic behavior of system maintenance operations are designed with activity diagrams and incorporated in the availability model. In Candy, activity diagrams are translated into SRNs and synchronized with the related SRNs to compose the entire availability model. The proposed synchronization method is not discussed in any