Ernst Juhnke

Multi-objective Scheduling of BPEL Workflows in Geographically Distributed Clouds

In this paper, a novel scheduling algorithm for Cloud-based workflow applications is presented. If the constituent workflow tasks are geographically distributed - hosted by different Cloud providers or data centers of the same provider - data transmission can be the main bottleneck. The algorithm therefore takes data dependencies between workflow steps into account and assigns them to Cloud resources based on the two conflicting objectives of cost and execution time according to the preferences of the user. Our implementation is based on BPEL, an industry standard for workflow modeling, and does not require any changes to the standard. It is based on, but not limited to, the Active BPEL engine and Amazons Elastic Compute Cloud. To automatically adapt the scheduling decisions to network-related changes, the data transmission speed between the available resources is monitored continuously. Experimental results for a real-life workflow from a medical domain indicate that both the workflow execution times and the corresponding costs can be reduced significantly.

A scalable service-oriented architecture for multimedia analysis, synthesis and consumption

Although Service-Oriented Architectures (SOAs) were not designed for multimedia processing, they speed up the development of distributed multimedia applications by allowing the composition or reconfiguration of existing services. For example, the Business Process Execution Language for Web Services (BPEL) is a powerful tool to orchestrate, model and execute workflows. However, due to its process-oriented approach, it is not directly applicable to data-intensive applications, such as those from the multimedia domain. In this paper, a comprehensive service-oriented infrastructure for multimedia applications is presented that (a) overcomes some drawbacks of BPEL for data-intensive applications and (b) provides tools that further ease the development and use of web services for a broad scope of multimedia applications covering video content analysis, audio analysis and synthesis and multimedia consumption. The proposed service-oriented infrastructure can be easily integrated into existing business processes by using BPEL. A dynamic allocation of cloud computing resources ensures the scalability of a multimedia application. To allow efficient and flexible data transfers in BPEL workflows, an implementation of the Flexible SOAP with Attachments (Flex-SwA) architecture is used that allows data transmission in conjunction with SOAP messages. The protocol requirements of services in the case of real-time, streaming or file transfer can be described by a communication policy. Three use cases of multimedia applications are evaluated.

Fault-Tolerant BPEL Workflow Execution via Cloud-Aware Recovery Policies

BPEL is the de facto standard for business process modeling in todays enterprises and is a promising candidate for the integration of business and scientific applications that run in Grid or Cloud environments. In these distributed infrastructures, the occurrence of faults is quite likely. Without sophisticated fault handling, workflows are frequently abandoned due to software or hardware failures, leading to a waste of CPU hours. The fault handling mechanisms provided by BPEL are well suited for handling faults of the business logic, but infrastructure-induced errors should be handled automatically to avoid over-complication of workflow design and keep concerns separated. This paper identifies classes of faults that can be resolved automatically by the infrastructure, and provides a policy-based approach to configure this automatic behavior without the need for adding explicit fault handling mechanisms to the BPEL process. The proposed approach provides automatic redundancy of services using a Cloud infrastructure to allow substitution of defective services. An implementation based on the ActiveBPEL engine and Amazons Elastic Compute Cloud is presented.

AOP4CSM: An Aspect-Oriented Programming Approach for Cloud Service Monitoring

Monitoring is important for managing a Cloud computing environment. This task should be performed without modifying the implementation of the offered Cloud services. In this paper, a monitoring approach that neither modifies the server implementation nor the client implementation is presented. The proposed approach, called AOP4CSM, is based on aspect-oriented programming and monitors quality-of-service parameters of the Software-as-a-Service layer. The use of AOP4CSM is exemplified in the context of fault tolerance. Experimental results show the efficiency of AOP4CSM (very low overhead) and its advantages when applied to provide fault tolerance (good recovery decision).

An identity-based security infrastructure for Cloud environments

This paper presents a novel security infrastructure for deploying and using service-oriented Cloud applications securely without having to face the complexity associated with certificate management. The proposal is based on an identity-based cryptographic approach that offers an independent setup of security domains and does not require a trust hierarchy compared to other identity-based cryptographic systems. The service URLs can be used as public keys, such that creating a secure connection to a service is very simple. A comparison between traditional approaches and identity-based cryptography with respect to data transfer requirements is presented.

Data Flow Driven Scheduling of BPEL Workflows Using Cloud Resources

In this paper, an approach to assign BPEL workflow steps to available resources is presented. The approach takes data dependencies between workflow steps and the utilization of resources at runtime into account. The developed scheduling algorithm simulates whether the makespan of workflows could be reduced by providing additional resources from a Cloud infrastructure. If yes, Cloud resources are automatically set up and used to increase throughput. The proposed approach does not require any changes to the BPEL standard. An implementation based on the ActiveBPEL engine and Amazons Elastic Compute Cloud is presented. Experimental results for a real-life workflow from a medical application indicate that workflow execution times can be reduced significantly.

DAVO: A Domain-Adaptable, Visual BPEL4WS Orchestrator

The Business Process Execution Language for Web Services (BPEL4WS) is the de facto standard for the composition of web services into complex, valued-added workflows in both industry and academia. Since the composition of web services into a workflow is challenging and error-prone, several graphical BPEL4WS workflow editors have been developed. These tools focus on the composition process and the visualization of workflows and mainly address the needs of web service experts.To increase the acceptance of BPEL4WS in new application domains, it is mandatory that non web service experts are also empowered to easily compose web services into a workflow. This paper presents the Domain-Adaptable Visual Orchestrator (DAVO), a graphical BPEL4WS workflow editor which offers a domain-adaptable data model and user interface. DAVO can be easily customized to domain needs and thus is suitable for non web service experts.

Efficient data transmission in service workflows for distributed video content analysis

Workflows of web services orchestrated by the Business Process Execution Language (BPEL) have been successfully used in many business applications. Although these technologies were not originally designed for multimedia processing, they offer advantages to speed up the development of distributed multimedia analysis applications by allowing the composition or reconfiguration of existing services. However, in the case of service-oriented distributed video content analysis, a huge amount of binary data has to be transferred between different services. As a consequence, service orchestration based on BPEL leads to a performance bottleneck due to indirect message and data transport: the workflow engine receives results (which are potentially very large) from finished services and passes them to a subsequent service. In this paper, we present two novel approaches based on our previously developed Flex-SwA framework to model the binary data transmission between services in BPEL workflows. The proposed approaches circumvent the performance bottleneck at the orchestrating engine and provide efficient possibilities to transfer large data amounts as well as large data units. The first approach models the data flow in BPEL; the services exchange data directly. The second approach models the data flow outside of the BPEL engine and shifts it completely to the Flex-SwA framework. Experimental results for a video analysis workflow demonstrate the advantages of the proposed approaches.

Exposing validity periods of prices for resource consumption to web service users via temporal policies

Web services usually have functional as well as non-functional properties. Functional properties, such as the WSDL description, are usually static, whereas non-functional properties are often dynamic and thus vary over time. One of these non-functional properties are prices for using a web service or the resources it consumes. It is desirable to dynamically set prices depending on criteria such as the time of day or usage patterns and to expose pricing information in several ways. In this paper, we introduce an extended version of our previously proposed temporal policy language to handle these requirements. The extension provides the possibility of adding the exposition of validity periods to service users by weaving an attribute from the temporal policy namespace to WS-Policies. Furthermore, a schema for temporal policies and a state diagram are introduced. A use case from the area of pricing high performance computing resources is presented to demonstrate that exposing validity periods to service users enables them to automatically estimate how long they can use computing resources for a given price.

LCDL: an extensible framework for wrapping legacy code

If legacy code has to be integrated into an application, it is often necessary to call this code available as source code written in a particular programming language or available in binary format for a particular computing platform from another programming language or from a remote machine. For this reason, wrapping code has to be developed for each source code library or binary code to be integrated. This paper presents an extensible framework that supports legacy code integration by modeling legacy code not only in a way that is programming (language) independent, but also by supporting different input and output types and bindings. This aim is achieved by the use of an integrated plug-in mechanism.