Tim Dörnemann

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.

Secure on-demand grid computing

In this paper, a novel approach for enabling Grid users to autonomously install and use custom software on demand using an image creation station is presented, while at the same time offering new security mechanisms to protect both software and data from other Grid users and external attackers. An automated dynamic firewalling mechanism enables both virtual organization and user-based network security setups. Furthermore, the Grid environment is partitioned into several zones to protect local cluster resources from compromised Grid middleware. To enable the secure integration of this Grid environment into existing business processes, an extension of BPEL is presented which allows the execution of GSI secured Grid services in combination with existing business web services. The workflow engine transparently handles proxy certificate creation and monitors proxy certificate lifetime. An implementation based on the Globus Toolkit 4, the Sun Grid Engine and the ActiveBPEL Engine is presented. A performance evaluation of the critical components of the new Grid setup is provided.

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.

Composition and Execution of Secure Workflows in WSRF-Grids

BPEL is the de-facto standard for business process modeling in todays enterprises and is a promising candidate for the integration of business and Grid applications. While BPEL works well for traditional web services, it has a number of drawbacks with respect to the more complex world of WSRF- based Grid computing, especially where security is concerned. In this paper, a solution that extends the BPEL security approach to encompass secure Grid application interactions is presented. The proposed approach is capable of handling both web service and Grid service resources and their corresponding security mechanisms. The BPEL language is extended by security-related settings. An implementation of a GSI-compliant BPEL engine that can also manage the lifetime of proxy certificates is presented.

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.

Omnivore: Integration of Grid Meta-Scheduling and Peer-to-Peer Technologies

Dedicated servers remain to be a common constituent of Grid job scheduling architectures, forcing site administrators to make compromises between administrative expenses and system reliability. Apart from requiring administrative attention, dedicated servers create single points of failure and should not be subjected to network churn. This paper presents the design and implementation of Omnivore, a fully decentralized job scheduling system, built on a peer-to-peer based meta-scheduler. Omnivore is able to cope both with node failures and network churn, eliminating the need for central administration and continuous resource availability. It is integrated into the Grid landscape (especially the Globus Toolkit 4) by means of the GridWay meta- scheduler to provide scalable distributed scheduling, replicated storage and system monitoring capabilities. Results obtained from an experimental evaluation of our implementation show that Omnivore is both scalable and resilient in the presence of node failures and network churn.

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.

Orchestration of Time-Constrained BPEL4WS workflows

The adoption of service-oriented architectures based on Web services in industrial automation promises increased interoperability and flexibility. The orchestration of existing Web services to workflows is a challenging task which is complicated by the fact that manufacturing processes have time constraints, especially real-time constraints. This paper presents the time-constrained services (TiCS) Modeler which supports the assisted orchestration of BPEL4WS workflows with time constraints. The presented prototypical implementation is based on a formal derivation of the time constraints of a workflow.