Building Reliable Web Services: Methodology, Composition, Modeling and Experiment

1. Building Reliable Web Services: Methodology,Composition, Modeling and Experiment Pat. P. W. Chan Department of Computer Science and Engineering The Chinese University of Hong Kong 23 October 2007

2. Outline • Introduction to Web Services • Problem Statement • Methodologies for Web Service Reliability • New Reliable Web Service Paradigm • Web Service Composition Algorithm • 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. Round Robin

7. Parallel N-Version Programming

8. Recovery Block

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

10. 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.

11. System Architecture

12. 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

13. Experimental Setup

14. 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.

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

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

17. Experimental Result with Recovery Block (failures / response time in ms)

18. Web Service Composition Algorithm • N-version programming • Reliable • Efficient • Composition • WSDL • WSCI • Verification • BPEL • Petri-Net

19. WSDL <?xmlversion="1.0" encoding="UTF-8"?> … <portTypename=“BRF"> <operationname=“shortestpath"> <inputmessage="tns:startpointDestination"/> <outputmessage="tns:pathArray"/> </operation> <operationname=“addCheckpoint"> <inputmessage="tns:pathArray"/> <outputmessage="tns:addAcknowledgement"/> </operation> … </operation> </portType> </definitions>

20. WSCI <correlationname=“pathCorrelation”property=“tns:pathID”></correlation> <interfacename=“busAgent”> <processinstantiation="message"> <sequence> <actionname="ReceiveStartpointDest“role="tns:busAgent“ operation="tns:BRF/shortestpath"> </action> <actionname="Receivecheckpoint“role=" tns:busAgent“ operation="tns:BRF/addCheckpoint"> <correlatecorrelation=“tns: pathCorrelation”/> <callprocess=“tns:SearchPath”/> </action> </sequence> </process> …

22. CP4 CP7 CP10 Else, till the root of WSCI Web service composition • Output • Operation in WSDL • Find the output information in CP1 (Web service component) • If Input of the operation == required input CP1 • Else • search in the WSCI of CP1 to find action == operation • Get the pervious action involved • Search in WSDL to find operation == action • If Input of the operation == required input

25. Petri-Net– Basic Activities

26. Petri-Net– Structure Activities

27. Composed Petri-Net

34. Petri-Net (Four identical replicas)

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

36. Petri-Net (Recovery Block)

37. 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

38. 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

39. Outcome (SHARPE)

40. Conclusion • Surveyed replication and design diversity techniques for reliable services. • Proposed a hybrid approach to improving the availability of Web services. • Proposed a Web service composition algorithm and verified by Petri-Net. • Carried out a series of experiments to evaluate the availability and reliability of the proposed Web service system.

41. Q&A