A Classification of BPEL Extensions

The Business Process Execution Language (BPEL) has emerged as de-facto standard for business processes implementation. This language is designed to be extensible for including additional valuable features in a standardized manner. There are a number of BPEL extensions available. They are, however, neither classified nor evaluated with respect to their compliance to the BPEL standard. This article fills this gap by providing a framework for classifying BPEL extensions, a classification of existing extensions, and a guideline for designing BPEL extensions

Runtime Adaptation of Scientific Service Workflows

Software landscapes are rather subject to change than being complete after having been built. Changes may be caused by a modified customer behavior, the shift to new hardware resources, or otherwise changed requirements. In such situations, several challenges arise. New architectural models have to be designed and implemented, existing software has to be integrated, and, finally, the new software has to be deployed, monitored, and, where appropriate, optimized during runtime under realistic usage scenarios. All of these situations often demand manual intervention, which causes them to be error-prone. This thesis addresses these types of runtime adaptation. Based on service-oriented architectures, an environment is developed that enables the integration of existing software (i.e., the wrapping of legacy software as web services). A workflow modeling tool that aims at an easy-to-use approach by separating the role of the workflow expert and the role of the domain expert. After the development of workflows, tools that observe the executing infrastructure and perform automatic scale-in and scale-out operations are presented. Infrastructure-as-a-Service providers are used to scale the infrastructure in a transparent and cost-efficient way. The deployment of necessary middleware tools is automatically done. The use of a distributed infrastructure can lead to communication problems. In order to keep workflows robust, these exceptional cases need to treated. But, in this way, the process logic of a workflow gets mixed up and bloated with infrastructural details, which yields an increase in its complexity. In this work, a module is presented that can deal automatically with infrastructural faults and that thereby allows to keep the separation of these two layers. When services or their components are hosted in a distributed environment, some requirements need to be addressed at each service separately. Although techniques as object-oriented programming or the usage of design patterns like the interceptor pattern ease the adaptation of service behavior or structures. Still, these methods require to modify the configuration or the implementation of each individual service. On the other side, aspect-oriented programming allows to weave functionality into existing code even without having its source. Since the functionality needs to be woven into the code, it depends on the specific implementation. In a service-oriented architecture, where the implementation of a service is unknown, this approach clearly has its limitations. The request/response aspects presented in this thesis overcome this obstacle and provide a SOA-compliant and new methods to weave functionality into the communication layer of web services. The main contributions of this thesis are the following: Shifting towards a service-oriented architecture: The generic and extensible Legacy Code Description Language and the corresponding framework allow to wrap existing software, e.g., as web services, which afterwards can be composed into a workflow by SimpleBPEL without overburdening the domain expert with technical details that are indeed handled by a workflow expert. Runtime adaption: Based on the standardized Business Process Execution Language an automatic scheduling approach is presented that monitors all used resources and is able to automatically provision new machines in case a scale-out becomes necessary. If the resource's load drops, e.g., because of less workflow executions, a scale-in is also automatically performed. The scheduling algorithm takes the data transfer between the services into account in order to prevent scheduling allocations that eventually increase the workflow's makespan due to unnecessary or disadvantageous data transfers. Furthermore, a multi-objective scheduling algorithm that is based on a genetic algorithm is able to additionally consider cost, in a way that a user can define her own preferences rising from optimized execution times of a workflow and minimized costs. Possible communication errors are automatically detected and, according to certain constraints, corrected. Adaptation of communication: The presented request/response aspects allow to weave functionality into the communication of web services. By defining a pointcut language that only relies on the exchanged documents, the implementation of services must neither be known nor be available. The weaving process itself is modeled using web services. In this way, the concept of request/response aspects is naturally embedded into a service-oriented architecture

Supporting Quality of Service in Scientific Workflows

While workflow management systems have been utilized in enterprises to support businesses for almost two decades, the use of workflows in scientific environments was fairly uncommon until recently. Nowadays, scientists use workflow systems to conduct scientific experiments, simulations, and distributed computations. However, most scientific workflow management systems have not been built using existing workflow technology; rather they have been designed and developed from scratch. Due to the lack of generality of early scientific workflow systems, many domain-specific workflow systems have been developed. Generally speaking, those domain-specific approaches lack common acceptance and tool support and offer lower robustness compared to business workflow systems. In this thesis, the use of the industry standard BPEL, a workflow language for modeling business processes, is proposed for the modeling and the execution of scientific workflows. Due to the widespread use of BPEL in enterprises, a number of stable and mature software products exist. The language is expressive (Turingcomplete) and not restricted to specific applications. BPEL is well suited for the modeling of scientific workflows, but existing implementations of the standard lack important features that are necessary for the execution of scientific workflows. This work presents components that extend an existing implementation of the BPEL standard and eliminate the identified weaknesses. The components thus provide the technical basis for use of BPEL in academia. The particular focus is on so-called non-functional (Quality of Service) requirements. These requirements include scalability, reliability (fault tolerance), data security, and cost (of executing a workflow). From a technical perspective, the workflow system must be able to interface with the middleware systems that are commonly used by the scientific workflow community to allow access to heterogeneous, distributed resources (especially Grid and Cloud resources). The major components cover exactly these requirements: Cloud Resource Provisioner Scalability of the workflow system is achieved by automatically adding additional (Cloud) resources to the workflow system’s resource pool when the workflow system is heavily loaded. Fault Tolerance Module High reliability is achieved via continuous monitoring of workflow execution and corrective interventions, such as re-execution of a failed workflow step or replacement of the faulty resource. Cost Aware Data Flow Aware Scheduler The majority of scientific workflow systems only take the performance and utilization of resources for the execution of workflow steps into account when making scheduling decisions. The presented workflow system goes beyond that. By defining preference values for the weighting of costs and the anticipated workflow execution time, workflow users may influence the resource selection process. The developed multiobjective scheduling algorithm respects the defined weighting and makes both efficient and advantageous decisions using a heuristic approach. Security Extensions Because it supports various encryption, signature and authentication mechanisms (e.g., Grid Security Infrastructure), the workflow system guarantees data security in the transfer of workflow data. Furthermore, this work identifies the need to equip workflow developers with workflow modeling tools that can be used intuitively. This dissertation presents two modeling tools that support users with different needs. The first tool, DAVO (domain-adaptable, Visual BPEL Orchestrator), operates at a low level of abstraction and allows users with knowledge of BPEL to use the full extent of the language. DAVO is a software that offers extensibility and customizability for different application domains. These features are used in the implementation of the second tool, SimpleBPEL Composer. SimpleBPEL is aimed at users with little or no background in computer science and allows for quick and intuitive development of BPEL workflows based on predefined components

Virtual Machine Lifecycle Management in Grid and Cloud Computing

Virtualisierungstechnologie ist die Grundlage für zwei wichtige Konzepte: Virtualized Grid Computing und Cloud Computing. Ersteres ist eine Erweiterung des klassischen Grid Computing. Es hat zum Ziel, die Anforderungen kommerzieller Nutzer des Grid hinsichtlich der Isolation von gleichzeitig ausgeführten Batch-Jobs und der Sicherheit der zugehörigen Daten zu erfüllen. Dabei werden Anwendungen in virtuellen Maschinen ausgeführt, um sie voneinander zu isolieren und die von ihnen verarbeiteten Daten vor anderen Nutzern zu schützen. Darüber hinaus löst Virtualized Grid Computing das Problem der Softwarebereitstellung, eines der bestehenden Probleme des klassischen Grid Computing. Cloud Computing ist ein weiteres Konzept zur Verwendung von entfernten Ressourcen. Der Fokus dieser Dissertation bezüglich Cloud Computing liegt auf dem “Infrastructure as a Service Modell”, das Ideen des (Virtualized) Grid Computing mit einem neuartigen Geschäftsmodell kombiniert. Dieses besteht aus der Bereitstellung von virtuellen Maschinen auf Abruf und aus einem Tarifmodell, bei dem lediglich die tatsächliche Nutzung berechnet wird. Der Einsatz von Virtualisierungstechnologie erhöht die Auslastung der verwendeten (physischen) Rechnersysteme und vereinfacht deren Administration. So ist es beispielsweise möglich, eine virtuelle Maschine zu klonen oder einen Snapshot einer virtuellen Maschine zu erstellen, um zu einem definierten Zustand zurückkehren zu können. Jedoch sind noch nicht alle Probleme im Zusammenhang mit der Virtualisierungstechnologie gelöst. Insbesondere entstehen durch den Einsatz in den sehr dynamischen Umgebungen des Virtualized Grid Computing und des Cloud Computing neue Herausforderungen für die Virtualisierungstechnologie. Diese Dissertation befasst sich mit verschiedenen Aspekten des Einsatzes von Virtualisierungstechnologie in Virtualized Grid und Cloud Computing Umgebungen. Zunächst wird der Lebenszyklus von virtuellen Maschinen in diesen Umgebungen untersucht, und es werden Modelle dieses Lebenszyklus entwickelt. Anhand der entwickelten Modelle werden Probleme identifiziert und Lösungen für diese Probleme entwickelt. Der Fokus liegt dabei auf den Bereichen Speicherung, Bereitstellung und Ausführung von virtuellen Maschinen. Virtuelle Maschinen werden üblicherweise in so genannten Disk Images, also Abbildern von virtuellen Festplatten, gespeichert. Dieses Format hat nicht nur Einfluss auf die Speicherung von größeren Mengen virtueller Maschinen, sondern auch auf deren Bereitstellung. In den untersuchten Umgebungen hat es zwei konkrete Nachteile: es verschwendet Speicherplatz und es verhindert eine effiziente Bereitstellung von virtuellen Maschinen. Maßnahmen zur Steigerung der Sicherheit von virtuellen Maschinen haben auf alle drei genannten Bereiche Einfluss. Beispielsweise sollte vor der Bereitstellung einer virtuellen Maschine geprüft werden, ob die darin installierte Software noch aktuell ist. Weiterhin sollte die Ausführungsumgebung Möglichkeiten bereitstellen, um die virtuelle Infrastruktur wirksam zu überwachen. Die erste in dieser Dissertation vorgestellte Lösung ist das Konzept der Image Composition. Es beschreibt die Komposition eines kombinierten Disk Images aus mehreren Schichten. Dadurch können Teile der einzelnen Schichten, die von mehreren virtuellen Maschinen verwendet werden, zwischen diesen geteilt und somit der Speicherbedarf für die Gesamtheit der virtuellen Maschinen reduziert werden. Der Marvin Image Compositor ist die Umsetzung dieses Konzepts. Die zweite Lösung ist der Marvin Image Store, ein Speichersystem für virtuelle Maschinen, das nicht auf den traditionell genutzten Disk Images basiert, sondern die darin enthaltenen Daten und Metadaten auf eine effiziente Weise getrennt voneinander speichert. Weiterhin werden vier Lösungen vorgestellt, die die Sicherheit von virtuellen Maschine verbessern können: Der Update Checker ist eine Lösung, die es ermöglicht, veraltete Software in virtuellen Maschinen zu identifizieren. Dabei spielt es keine Rolle, ob die jeweilige virtuelle Maschine gerade ausgeführt wird oder nicht. Die zweite Sicherheitslösung ermöglicht es, mehrere virtuelle Maschinen, die auf dem Konzept der Image Composition basieren, zentral zu aktualisieren. Das bedeutet, dass die einmalige Installation einer neuen Softwareversion ausreichend ist, um mehrere virtuelle Maschinen auf den neuesten Stand zu bringen. Die dritte Sicherheitslösung namens Online Penetration Suite ermöglicht es, virtuelle Maschinen automatisiert nach Schwachstellen zu durchsuchen. Die Überwachung der virtuellen Infrastruktur auf allen Ebenen ist der Zweck der vierten Sicherheitslösung. Zusätzlich zur Überwachung ermöglicht diese Lösung auch eine automatische Reaktion auf sicherheitsrelevante Ereignisse. Schließlich wird ein Verfahren zur Migration von virtuellen Maschinen vorgestellt, welches auch ohne ein zentrales Speichersystem eine effiziente Migration ermöglicht