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Pat. P. W. Chan, Michael R. Lyu Department of Computer Science and Engineering

Reliable Web Services: Methodology, Experiment and Modeling International Conference on Web Services (ICWS 2007). Miroslaw Malek Department of Computer Science and Engineering Humboldt University Berlin, Germany. Pat. P. W. Chan, Michael R. Lyu Department of Computer

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Pat. P. W. Chan, Michael R. Lyu Department of Computer Science and Engineering

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  1. Reliable Web Services: Methodology, Experiment and ModelingInternational Conference on Web Services (ICWS 2007) Miroslaw Malek Department of Computer Science and Engineering Humboldt University Berlin, Germany Pat. P. W. Chan, Michael R. Lyu Department of Computer Science and Engineering The Chinese University of Hong Kong Presented by Pat Chan

  2. Outline • Introduction to Web Services • Problem Statement • Methodologies for Web Service Reliability • New Reliable Web Service Paradigm • Optimal Parameters • Experimental Results and Discussion • Conclusion

  3. Introduction • Service-oriented computing is becoming a reality. • The problems of service dependability, security and timeliness are becoming critical. • We propose experimental settings and offer a roadmap to dependable Web services.

  4. Problem Statement • Fault-tolerant techniques • Replication • Diversity • Replication is one of the efficient ways for providing reliable systems by time or space redundancy. • Increasing the availability of distributed systems • Key components are re-executed or replicated • Protect against hardware malfunctions or transient system faults • Another efficient technique is design diversity • Employ independently designed software systems or services with different programming teams, • Defend against permanent software design faults. • We focus on the analysis of the replication techniques when applied to Web services. • A generic Web service system with spatial as well as temporal replication is proposed and investigated.

  5. Replication Manager Web Service RR Algorithm / Voting Web Service Web Service IIS Application IIS IIS Database WatchDog Application Application Invoke web service Database Database Client Port Application UDDI Update the WSDL Register Database Registry Keep check the availability of all the web. If Web service failed, update the list of availability of Web services WSDL Look up Get WSDL Proposed Paradigm

  6. Web Service Web Service Web Service Web Service Web Service Web Service Web Service IIS IIS IIS IIS IIS IIS IIS Application Application Application Application Application Application Application Database Database Database Database Database Database Database Web Service IIS Application Database Proposed Paradigm • Round Robin • Parallel N-Version Majority result Voting Client

  7. Experiments • A series of experiments are designed and performed for evaluating the reliability of the Web service,

  8. Testing system • Best Route Finding. • Provide traveling suggestions for users. • Starting point and destination. • The system needs to provide the best route and the price for the users.

  9. System Architecture

  10. Experimental Setup • Examine the computation to communication ratio • Examine the request frequency to limit the load of the server to 75% • Fix the following parameters • Computation to communication ratio (e.g 10:1) • Request frequency

  11. Experimental Setup

  12. Experiment Parameters • Fault mode • Temporary (fault probability: 0.01) • Permanent (fault probability: 0.001) • Experiment time 5 days (7200 requests) • Measure: • Number of failures • Average response time (ms) • Failure definition: • 5 retries are allowed. If there is still no correct result from the Web service after 5 retries, it is considered as a failure.

  13. Experimental Result with Round-robin (failures / response time in ms)

  14. Experimental Result with N-Version (failures / response time in ms)

  15. Varying the parameters • Number of tries • Timeout period for retry in single server • Timeout period for retry in our paradigm • Polling frequency • Number of replicas • Load of server

  16. Number of tries

  17. Timeout period for retry in single server

  18. Timeout period for retry in single server # of failure Timeout period

  19. Timeout period for retry in our paradigm

  20. Polling frequency

  21. Polling frequency # of failure Polling frequency

  22. Number of Replicas

  23. Load of Web Server

  24. Summary of Parameters • Number of tries = 2 • Timeout period for retry in single server = 10s • Timeout period for retry in our paradigm = 5s • Polling frequency = 10 request per min • Number of replicas = 3 • Load of server = < 75%

  25. Petri-Net (Four identical replicas)

  26. Petri-Net (N-version Web service with voting)

  27. λN (1-c1)μ* (1-c1)μ* S F μ*c2 (1-c1)μ* μ*c2 S-1 S-2 S-n λ* λ* λ* (a) (1-c1)μ1 μ1c2 P1 (1-c2)μ1 λ1 S-j S-j-1 F μ2c2 (1-c2)μ2 λ2 (1-c1)μ2 P2 (b) Reliability Model

  28. ID Description Value λn Network failure rate 0.02 λ* Web service failure rate 0.025 λ1 Resource problem rate 0.142 λ2 Entry point failure rate 0.150 μ* Web service repair rate 0.286 μ1 Resource problem repair rate 0.979 μ2 Entry point failure repair rate 0.979 C1 Probability that the RM response on time 0.9 C2 Probability that the server reboot successfully 0.9 Reliability Model

  29. Outcome (SHARPE)

  30. Conclusion • Surveyed replication and design diversity techniques for reliable services. • Proposed a hybrid approach to improving the availability of Web services. • Carried out a series of experiments to evaluate the availability and reliability of the proposed Web service system. • Optimal parameters are obtained.

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