1 Developing Aerospace Applications with a Reliable Web Services Paradigm Pat. P. W. Chan and Michael R. Lyu Department of Computer Science and Engineering The Chinese University of Hong Kong IEEE 2008 Aerospace Conference

2 Outline  Introduction  Problem Statement  Methodologies for Web Service Reliability  New Reliable Web Service Paradigm Optimal Parameters Experimental Results  Web Service Composition Algorithm Experimental Results Discussion  Modeling of the Paradigm  Conclusion and Future Work

3 Introduction  Web services provide an efficient and convenient way for service provisioning, exchanging and aggregating, which facilitate a resourceful platform for the aerospace industry.  Complex synthesis of various aerospace technologies and sciences can be provided in the form of Web services.  In aerospace area, reliability is an ultimately important issue.  Existing Web service model needs to be extended to assure reliability.  We propose a paradigm with a roadmap to dependable Web services. Introduction

4 Problem Statement  Fault-tolerant techniques Replication Diversity  Replication is one of the efficient ways for providing reliable systems by time or space redundancy. Increase the availability of distributed systems Key components are re-executed or replicated Protect against hardware malfunctions or transient system failures  Another potential 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. Introduction

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

6 Different Approaches  Replication Round-robin scheduling algorithm  Design Diversity N-version programming Recovery block Reliable Web Service Paradigm

7 Replication: Round-robin Reliable Web Service Paradigm

8 RM sends message to the Web Service Update the Web service availability list Does not get reply Map the new address to the WSDL after RR System Failure Gets reply All Services failed Work Flow of the Replication Manager Reliable Web Service Paradigm

9 Design Diversity: Parallel N-Version Programming Reliable Web Service Paradigm

10 Design Diversity: Recovery Block Reliable Web Service Paradigm

11 Experiments Variations  A series of experiments are designed and performed for evaluating the reliability of the Web service. Spatial replication Reboot Retry Reliable Web Service Paradigm

12 System Testing  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. Reliable Web Service Paradigm

13 System Architecture Reliable Web Service Paradigm

14 Experimental Setup Communication time: Computation time 143:14 (10:1) Total requests and frequency10000 requests (1 per min) Load78.5% Timeout period of retry1 min Timeout for Web service in RM1s (Web service specific) Polling frequency10 requests per min Number of replicas5 Max number of retries5 Round-robin rate1 s Reliable Web Service Paradigm

15 Experimental Results (1) Web Service Composition

16 Experimental Results (2) Web Service Composition

17 Experimental Results (3) Web Service Composition

18 Experimental Results (4) Web Service Composition

19 Summary of the Proposed Paradigm  Temporal replication (reboot or retry) improves the reliability.  Spatial replication further improves the reliability of Web services.  N-version programming approach is the most effective choice. Reliable Web Service Paradigm

20 Web Service Composition Algorithm  N-version programming Reliability improvement Effective  Composition WSDL – Web Services Description Language WSCI – Web Services Choreography Interface  Verification BPEL – Business Process Execution Language Petri-Net Web Service Composition

21 … … WSDL Web Service Composition

22 <action name="ReceiveStartpointDest “ role="tns:busAgent “ operation="tns:BRF/shortestpath"> <action name="Receivecheckpoint “ role=" tns:busAgent “ operation="tns:BRF/addCheckpoint"> … WSCI Web Service Composition

23 Web Service Composition

24 1.Output 2.Operation in WSDL 3.Find the output information in CP1 (Web service component) 4.If Input of the operation == required input CP1 5.Else search in the WSCI of CP1 to find action == operation 6.Get the pervious action involved 7.Search in WSDL to find operation == action 8.If Input of the operation == required input CP4 Else, till the root of WSCI Web Service Composition CP7 CP10 Web Service Composition

25 Web Service Composition Search Agent Bus AgentTrain Agent Bus: KMB Train: MTR Starting P1 Starting P2 Web Service Composed Tree

26 Web Service Composition

27 Petri-Net – Basic Activities Web Service Composition

28 Petri-Net – Structure Activities Web Service Composition

29 Composed Petri-Net Web Service Composition

30 Web Service Composition

31 Web Service Composition

32 Summary of the Web Service Composition Algorithm  The composition algorithm is proposed with the use of WSDL and WSCL  The BPEL of the composed Web services are generated  Petri-Net is employed to avoid deadlock  Acceptance tests are set for checking the correctness  Experiments are performed Efficient Accurate Deadlock-free Web Service Composition

33 (a) (b) P1P1 λ1λ1 μ1c2μ1c2 S-j P2P2 μ2c2μ2c2 λ2λ2 S-j-1 S S-n F λNλN μ*c 2 (1-c 1 )μ* λ*λ* S-1S-2 λ*λ* μ*c2μ*c2 λ*λ* (1-c 1 )μ* F (1-c 1 )μ 1 (1-c 1 )μ 2 (1-c 2 )μ 1 (1-c 2 )μ 2 Reliability Model Modeling

34 Reliability Model IDDescriptionValue λnλn Network failure rate0.02 λ*Web service failure rate0.025 λ1λ1 Resource problem rate0.142 λ2λ2 Entry point failure rate0.150 μ*Web service repair rate0.286 μ1μ1 Resource problem repair rate0.979 μ2μ2 Entry point failure repair rate0.979 C1C1 Probability that the RM response on time0.9 C2C2 Probability that the server reboot successfully0.9 Modeling

35 Outcome (SHARPE) Modeling

36 Conclusions  Surveyed replication and design diversity techniques for reliable services and the state-of-the-art Web service composition algorithm.  Proposed a hybrid approach to improving the reliability 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.  Employ Markov chain to model the system and analyze its reliability and performance. Conclusion and Future Work

37 Future Work  Improve the current fault-tolerant techniques Current approach can deal with hardware and software failures. How about software fault detectors?  N-version programming Different providers provide different solutions. There is a problem in failover or switch between the Web Services.  Application Different requirements Realize in the Internet. Conclusion and Future Work

38 Q&A