A Taxonomy of Workflow Management Systems for Grid Computing

With the advent of Grid and application technologies, scientists and engineers are building more and more complex applications to manage and process large data sets, and execute scientific experiments on distributed resources. Such application scenarios require means for composing and executing complex workflows. Therefore, many efforts have been made towards the development of workflow management systems for Grid computing. In this paper, we propose a taxonomy that characterizes and classifies various approaches for building and executing workflows on Grids. We also survey several representative Grid workflow systems developed by various projects world-wide to demonstrate the comprehensiveness of the taxonomy. The taxonomy not only highlights the design and engineering similarities and differences of state-of-the-art in Grid workflow systems, but also identifies the areas that need further research.Comment: 29 pages, 15 figure

Perfomance Analysis and Resource Optimisation of Critical Systems Modelled by Petri Nets

Un sistema crítico debe cumplir con su misión a pesar de la presencia de problemas de seguridad. Este tipo de sistemas se suele desplegar en entornos heterogéneos, donde pueden ser objeto de intentos de intrusión, robo de información confidencial u otro tipo de ataques. Los sistemas, en general, tienen que ser rediseñados después de que ocurra un incidente de seguridad, lo que puede conducir a consecuencias graves, como el enorme costo de reimplementar o reprogramar todo el sistema, así como las posibles pérdidas económicas. Así, la seguridad ha de ser concebida como una parte integral del desarrollo de sistemas y como una necesidad singular de lo que el sistema debe realizar (es decir, un requisito no funcional del sistema). Así pues, al diseñar sistemas críticos es fundamental estudiar los ataques que se pueden producir y planificar cómo reaccionar frente a ellos, con el fin de mantener el cumplimiento de requerimientos funcionales y no funcionales del sistema. A pesar de que los problemas de seguridad se consideren, también es necesario tener en cuenta los costes incurridos para garantizar un determinado nivel de seguridad en sistemas críticos. De hecho, los costes de seguridad puede ser un factor muy relevante ya que puede abarcar diferentes dimensiones, como el presupuesto, el rendimiento y la fiabilidad. Muchos de estos sistemas críticos que incorporan técnicas de tolerancia a fallos (sistemas FT) para hacer frente a las cuestiones de seguridad son sistemas complejos, que utilizan recursos que pueden estar comprometidos (es decir, pueden fallar) por la activación de los fallos y/o errores provocados por posibles ataques. Estos sistemas pueden ser modelados como sistemas de eventos discretos donde los recursos son compartidos, también llamados sistemas de asignación de recursos. Esta tesis se centra en los sistemas FT con recursos compartidos modelados mediante redes de Petri (Petri nets, PN). Estos sistemas son generalmente tan grandes que el cálculo exacto de su rendimiento se convierte en una tarea de cálculo muy compleja, debido al problema de la explosión del espacio de estados. Como resultado de ello, una tarea que requiere una exploración exhaustiva en el espacio de estados es incomputable (en un plazo prudencial) para sistemas grandes. Las principales aportaciones de esta tesis son tres. Primero, se ofrecen diferentes modelos, usando el Lenguaje Unificado de Modelado (Unified Modelling Language, UML) y las redes de Petri, que ayudan a incorporar las cuestiones de seguridad y tolerancia a fallos en primer plano durante la fase de diseño de los sistemas, permitiendo así, por ejemplo, el análisis del compromiso entre seguridad y rendimiento. En segundo lugar, se proporcionan varios algoritmos para calcular el rendimiento (también bajo condiciones de fallo) mediante el cálculo de cotas de rendimiento superiores, evitando así el problema de la explosión del espacio de estados. Por último, se proporcionan algoritmos para calcular cómo compensar la degradación de rendimiento que se produce ante una situación inesperada en un sistema con tolerancia a fallos

Robustness of VoIP Systems

Katedra telekomunikační technik

Availability modeling and evaluation on high performance cluster computing systems

Cluster computing has been attracting more and more attention from both the industrial and the academic world for its enormous computing power, cost effective, and scalability. Beowulf type cluster, for example, is a typical High Performance Computing (HPC) cluster system. Availability, as a key attribute of the system, needs to be considered at the system design stage and monitored at mission time. Moreover, system monitoring is a must to help identify the defects and ensure the system\u27s availability requirement. In this study, novel solutions which provide availability modeling, model evaluation, and data analysis as a single framework have been investigated. Three key components in the investigation are availability modeling, model evaluation, and data analysis. The general availability concepts and modeling techniques are briefly reviewed. The system\u27s availability model is divided into submodels based upon their functionalities. Furthermore, an object oriented Markov model specification to facilitate availability modeling and runtime configuration has been developed. Numerical solutions for Markov models are examined, especially on the uniformization method. Alternative implementations of the method are discussed; particularly on analyzing the cost of an alternative solution for small state space model, and different ways for solving large sparse Markov models. The dissertation also presents a monitoring and data analysis framework, which is responsible for failure analysis and availability reconfiguration. In addition, the event logs provided from the Lawrence Livermore National Laboratory have been studied and applied to validate the proposed techniques

Guest editorial to the first international workshop on performability modelling of computer and communication systems

The papers in this issue of Performance Evaluation all deal with performability modelling of computer and communication systems. This was the topic of the First International Workshop on Performability Modelling of Computer and Communication Systems (PMCCS-1), held 7-8 February 1991, at the University of Twente, Enschede, the Netherlands

MACHS: Mitigating the Achilles Heel of the Cloud through High Availability and Performance-aware Solutions

Cloud computing is continuously growing as a business model for hosting information and communication technology applications. However, many concerns arise regarding the quality of service (QoS) offered by the cloud. One major challenge is the high availability (HA) of cloud-based applications. The key to achieving availability requirements is to develop an approach that is immune to cloud failures while minimizing the service level agreement (SLA) violations. To this end, this thesis addresses the HA of cloud-based applications from different perspectives. First, the thesis proposes a component’s HA-ware scheduler (CHASE) to manage the deployments of carrier-grade cloud applications while maximizing their HA and satisfying the QoS requirements. Second, a Stochastic Petri Net (SPN) model is proposed to capture the stochastic characteristics of cloud services and quantify the expected availability offered by an application deployment. The SPN model is then associated with an extensible policy-driven cloud scoring system that integrates other cloud challenges (i.e. green and cost concerns) with HA objectives. The proposed HA-aware solutions are extended to include a live virtual machine migration model that provides a trade-off between the migration time and the downtime while maintaining HA objective. Furthermore, the thesis proposes a generic input template for cloud simulators, GITS, to facilitate the creation of cloud scenarios while ensuring reusability, simplicity, and portability. Finally, an availability-aware CloudSim extension, ACE, is proposed. ACE extends CloudSim simulator with failure injection, computational paths, repair, failover, load balancing, and other availability-based modules