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Term Presentation Presented by Pat Chan 3 May 2006

Reliable Web Services by Fault Tolerant Techniques: Methodology, Experiment, Modeling and Evaluation. Term Presentation Presented by Pat Chan 3 May 2006. Outline. Introduction Problem Statement Methodologies for Web Service Reliability New Reliable Web Service Paradigm

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Term Presentation Presented by Pat Chan 3 May 2006

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  1. Reliable Web Services by Fault Tolerant Techniques: Methodology, Experiment, Modeling and Evaluation Term Presentation Presented by Pat Chan 3 May 2006

  2. Outline • Introduction • Problem Statement • Methodologies for Web Service Reliability • New Reliable Web Service Paradigm • Road Map for Experiment • Experimental Results and Discussion • Conclusion

  3. Introduction • Service-oriented computing is becoming a reality. • Web Service is a promoting technique in the internet. • The benefit of interoperability, reusability, and adaptability. • Reliability is an important issue. • Existing web service model needs to be extended to assure survivability and reliability. • We propose experimental settings and offer a roadmap to dependable Web services.

  4. Reliability • "a measure of the success with which the system conforms to some authoritative specification" • Guaranteed delivery • Duplicate elimination • Ordering • Crash tolerance • State synchronization

  5. What are Web Services ? • Self-contained, modular applications built on deployed network infrastructure including XML and HTTP • Use open standards for description (WSDL), discovery (UDDI) and invocation (SOAP)

  6. Web Services UDDI Internet WSDL WSDL HTTP/SOAP

  7. Inter Application Protocols Reliable Messaging Eventing Transactions Building Block Modules Directory Referral Security … Inspection … Routing License Description SOAP The Internet TCP/IP XML HTTP/SMTP Web Services Architecture

  8. Simplicity Dynamic Standard Web Services Web Services • Benefits of WS • Service-oriented • Highly accessible • Open specification • Easy integration Build common infrastructure reducing the barriers of business integration with lower costs and faster speed.

  9. Problems of Web Services • Transaction • Atomicity is not provided • Security • Insecure Internet transportation • Reliability • The internet is inherently unreliable • No single underlying “transport protocols” address all the reliability issues.

  10. 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. • By independently designing software systems or services with different programming teams, • Resort in defending 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.

  11. Methodologies for Reliable Web services -- Redundancy • Spatial redundancy • Static redundancy, all replicas are active at the same time and voting takes place to obtain a correct result. • Dynamic redundancy engages one active replica at one time while others are kept in an active or in standby state. • Temporal redundancy • Redundancy in time

  12. Methodologies for Reliable Web services -- Diversity • Protect redundant systems against common-mode failures • With different designs and implementations, common failure modes will probably cause different error effects. • N-version programming, recovery blocks…

  13. Failure Response Stages of Web Services • Fault confinement • Fault detection • Diagnosis • Fail-over • Reconfiguration • Recovery • Restart • Repair • Reintegration

  14. Fault Confinement Offline Online Fault Detection Fault Detection Failover Diagnosis Repair Recovery Reconfiguration Restart Reintegration

  15. Replication Manager 6. Invoke web service Web Service Web service selection algorithm • Create web services • Select primary web • service (PWS) Web Service Web Service IIS Application IIS IIS Database WatchDog Application Application Database Database • Keep check the availability of the PWS • If PWS failed, reselect the PWS. Client 3. Register 9. Update the WSDL Port Application UDDI Database Registry 4. Look up WSDL 5. Get WSDL Propose Paradigm

  16. Get reply Do not get reply Reselect a primary Web Service RM sends message to the Web Service All Service failed System Fail Map the new address to the WSDL Work Flow of the Replication Manager

  17. Road Map for Experiment Research • Redundancy in time • Redundancy in space • Sequentially • Parallel • Majority voting using N modular redundancy • Diversified version of different services

  18. Experiments • A series of experiments are designed and performed for evaluating the reliability of the Web service, • single service without replication, • single service with retry or reboot and, • service with spatial replication. • We will also perform retry or failover when the Web service is down.

  19. None Retry/ Reboot Failover Both (hybrid) Single service, no retry 0 -- -- -- Single service with retry -- 1 -- -- Single service with reboot -- 2 -- -- Spatial replication -- -- 3 4 Summary of the Experiments

  20. Parameters Current setting/metric Request frequency 1 req/min Polling frequency 5 ms Number of replicas 5 Client timeout period for retry 10 s Failure rate λ # failures/hour Load (profile of the program) % or load function Reboot time 10 min Failover time 1 s Parameters of the Experiments

  21. Experimental Results Retry 11.97% to 4.93% Reboot 11.97% to 6.44% Failover 11.97% to 3.56% Retry and Failover 11.97% to 2.59%

  22. Number of Failure When the Server is Normal Situation

  23. Number of Failure When the Server is Busy

  24. Number of Failure When the Server Reboots Periodically

  25. Network Level Fault Injection

  26. Reliability of the System Over Time

  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. SHARPE Reliability with different failure rate Failure rate 0.005 0.05 0.01 0.02 0.03 0.04

  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. • Developed the Reliability Model for the proposed system.

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