Survey of Adding Fault Tolerance to Service Oriented Architecture Ingrid Buckley 03/26/09

Agenda Fault Tolerance Problem Objective SOA –Web Services Layers Survey Analysis Conclusion References

Fault Tolerance There are many fault tolerance mechanisms which can be adopted in the design of a web service [Buc08]. Replication and redundancy and diversity are basic mechanisms that can be used in the design of web services. N-version programming and recovery block apply diversity by having several different implementations of software or hardware specifications, running in parallel to cope with errors or failures that could arise directly from a specific implementation or design.

Fault Tolerance Techniques –Detection –Diagnosis –Masking –Containment –Recovery We aim to identify how patterns can be applied to SOA. Fault Tolerance Software Mechanisms –Redundancy –Diversity –Recovery/Graceful Degradation –Checking and Monitoring –N-version Programming –Recovery Blocks (RB)

Problem Service Oriented Architectures are widely used in industry and government. The need to render them fault tolerant is increasingly necessary in order to apply them to safety critical applications. Currently, there is no systematic methodology to design fault tolerance in SOA.

Objective To understand and evaluate approaches that has been done in adding fault tolerance to the SOA

EXAMPLE Fig 1. SOA Layer with standards added

Survey Transparent Fault-Tolerant Web Services An approach was presented for a scheme that recovers in progress requests that do not require deterministic servers or changes to the clients –Implemented two performance enhancements to a client-transparent fault tolerant Web service scheme that is based on a hot standby backup front-end server and logging. –In the original implementation each node is a primary/backup pair and maintained its role as the primary or the backup for all requests for as long as both nodes were operational. This results in uneven utilization of the nodes. –The first enhancement would allow each node to serve as primary for some requests

Survey Backup for others with the use of Dual Server hosts scheme instead of assigning a server to either a backup or primary role. Showed improvement in terms of the idle CPU cycles time when processing request. The second enhancement handles requests for dynamic content and static content differently to help decrease overhead for later requests. This is done by allowing both backup and primary server to generate and send acknowledgments to clients instead of logging replies which increases message size. This reduced average latency because static replies eliminated the reply/logging of each request.

Survey Providing Reliable Web Services through Active Replication –A middleware is presented that provides reliable web services using active replication technique. –It uses a timestamp-based protocol to maintain the consistency of the replicas’ states uses a state machine approach and FIFO processing –Allows the replicas to reach an agreement in the order in which the clients’ requests are processed. – Each replica consists of a proxy web service site and a web service site –The Requests sent by clients are encapsulated in SOAP messages

Survey –Experiment measured the overheads –A comparison of this timestamp-based protocol and optimistic active replication protocol was done. –The result showed the former performed better when the mean processing time increases –the overhead decreases due to the reduced synchronization cost

Survey A Modular Architecture for Secure and Reliable Distributed Communication –Proposed the use to achieve secure and reliable messaging exchanges in distributed systems at the application layer of the SOA: WS-ReliableMessaging WS-Trust, WS-Security and WS-SecureConversation –An implementation on Apache Axis 2 platform was done. –This resulted in modular components that can be used separately or combined to send reliable and secure messages within distributed system

Survey Dynamic Web Service Composition: A New Approach in Building Reliable Web Service –This approach creates a dynamic Web service composition algorithm with verification using Petri-Nets. –Each Web service is described by WSDL and their interactions with other services are described by WSCI –The algorithm is comprised of Web services with the information provided by these two specification descriptions –They verify the Web service to be deadlock free with modeling the Web service as a Petri-Net. –Experiments were done to check the correctness and performance of the composed Web service.

Survey –Experiments were done to check the correctness and performance of the composed Web service using acceptance test. –BPEL is constructed to describe composition properties of the web services: Communication and specific behaviors –Result from experiments showed that all test cases were passed and no deadlock was observed in all cases.

Analysis ApproachStandardsContributionApplication Transparent Fault-Tolerant Web services WSDL, WSCIDecrease in Average latency More idle CPU cycles Web Services Providing Reliable Web Services through Active Replication SOAPIncrease Performance Decrease overhead reduced synchronization cost Middleware A Modular Architecture for Secure and Reliable Distributed Communication WS-ReliableMessaging WS-Trust, WS-Security WS-SecureConversation Increase reliability of messages Increase securing messages Apache Axis 2 application Dynamic Web Service Composition: A New Approach in Building Reliable Web Service WSDL, WSCI, BPELEliminated dead-locks Increased reliability Web Service Algorithm

Conclusion A detailed survey can help shed light on what has been done to add fault Tolerance to the SOA. Increase our knowledge of how to add Fault Tolerance to the SOA We can evaluate and analyze pass contributions to build upon them or realize new approaches. Systematic methodology that can be used to aid designers in building secure web services We intend to use patterns to add fault tolerance to Service Oriented Architectures.

References [Eze08] Onyeka Ezenwoye and S. Masoud Sadjadi. A language-based approach to addressing reliability in composite web services. In Proceedings of the 20th International Conference on Software Engineering and Knowledge Engineering (SEKE'2008), pages , San Francisco Bay, USA, July [Har08] Neil B. Harrison and Paris Avgeriou. Incorporating Fault Tolerance Tactics in Software Architecture Patterns. Proceedings of ACM. SERENE NewCastle, UK, November 17-19,2008. [W3c04] David Booth, et al. Web Services Architecture /wsa.pdf, February [Buc08] I. Buckley, E.B Fernandez, “A Survey of Fault Tolerance Patterns”, Department of Computer Science and Engineering, Florida Atlantic University, [Agh03] N. Aghdaie and Y. Tamir, Performance Optimizations for Transparent Fault-Tolerant Web Services, Proceedings of IEEE, [Ye07] X.Ye, Providing Reliable Web Services through Active Replication, Proceedings of IEEE, 6th ACIS International Conference on Computer and Information Science (ICIS), [Jay07] C.M. Jayalath and R.U. Fernando, A Modular Architecture for Secure and Reliable Distributed Communication, Proceedings of IEEE, Second International Conference on Availability, Reliability and Security (ARES’07), [Cha08] P. P. W. Chan and M. R. Lyu, Dynamic Web Service Composition: A New Approach in Building Reliable Web Service, Proceedings of IEEE, 22nd International Conference on Advanced Information Networking and Applications, 2008.

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