WS-DREAM: A Distributed Reliability Assessment Mechanism for Web Services

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WS-DREAM A Distributed Reliability Assessment
Mechanism for Web Services
Zibin Zheng, Michael R. LyuDepartment of
Computer Science EngineeringThe Chinese
University of Hong KongHong Kong, China
DSN 2008, Anchorage, Alaska, USA, 25 June, 2008
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Outlines

1. Introduction
2. Design
3. Implementation
4. Experiments
5. Conclusion

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1. Introduction

• Service-Oriented Architecture (SOA) is becoming
  popular.
• Usually built using Web services.
• Reliability of the service-oriented applications
  becomes difficult to be guaranteed.
• Remote Web services may contain faults.
• Remote Web services may become unavailable.
• The Internet environment is unpredictable.

We need to know whether the target Web services
are reliable or not before using them.
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1. Introduction

• Performance of Web services is different from
  different user locations.
• Service-oriented applications may be deployed to
  different locations after developed.

• Distributed reliability assessment on Web
  services is necessary.
• Difficult.
• Time consuming.
• Expensive.

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1. Introduction

• WS-DREAM A Distributed REliability Assessment
  Mechanism for Web Services.
• User-collaboration
• YouTube sharing videos.
• Wikipedia sharing knowledge.
• WS-DREAM sharing assessment results of target
  Web services.
• Obtain performance information of individual Web
  service from different locations for Web service
  selection and ranking.
• Assess fault tolerance replication strategies.

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2. Design

• 1. Assessment request
• 2. Load Applet
• 3. Create test cases
• 4. Test task scheduling
• 5. Client get test plans
• 6. Client run test plans
• 7. Send back results
• 8. Analyzing and return
• final results to client.

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2. Design

• Fairness. Different Web Services should have fair
  chances to be assessed.
• Distribution. Web Services should be assessed by
  users in as many geography locations as possible.
  
• Feasibility. Task assignment should dynamically
  adjust to the frequently changed number of users
  and number of test plans.
• Efficiency. The algorithm should be efficient and
  it should not slow down the testing progress.

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2. Design

• Identical and similar Web Services are becoming
  available in Internet ? redundant replicas for
  fault tolerance ? cheaper.
• Basic replication strategies.
• Parallel. The application sends requests to
  different replicas at the same time.
• Retry. The same Web Service will be tried one
  more time if it fails at first.
• Recovery Block (RB). Another standby Web Service
  will be tried in sequence if the primary Web
  Service fails.

  Parallel Retry RB
Parallel 1.Parallel 4.ParallelRetry 6. ParallelRB
Retry 5.RetryParallel 2.Retry 8.RetryRB
RB 7.RBParallel 9.RBRetry 3.RB
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2. Design

• 4. ParallelRetry 5. RetryParallel
• 6. ParallelRB. 7. RBParallel
• 8. RetryRB 9. RBRetry

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2. Design

• XML-based test plan design.

• Assess performance of different replication
  strategies.
• Includes several test cases.
• Created by WS-DREAM server and executed in the
  client-side.

6. ParallelRB. 7. RBParallel
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3. Implementation

• JDK Eclipse
• Client-side
• Java Applet
• Server-side
• an HTTP Web site (Apache HTTP Server)
• a TestCaseGenerator (JDK6.0 Axis library)
• a TestCoodinator (Java Servlet Tomcat 6.0)
• a MySQL database (Record testing results)

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4. Experiments

• A service user plans to employ several Web
  services in his commercial Web site.
• Six identical Amazon book displaying and selling
  Web Service for fault tolerance purpose. (a-us,
  a-jp, a-de, a-ca, a-fr and a-uk)
• A Global Weather Web Service to display currently
  weather information.
• A GeoIP Web Service to get geography information
  of Website visitors.

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4. Experiments

• 1. Assess the reliability of individual Web
  Services.

• Among all the 5443 failure cases
• 2986 failure cases are due to timeout (of larger
  than 10 seconds)
• 2456 failure cases are due to unavailable service
  (http code 503)
• 1 failure case is due to bad gateway (http code
  502).

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4. Experiments
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4. Experiments
2. Measure the performance of different
replication strategies.

• Strategy 1 (Parallel) provides the best RTT
  performance.
• The sequential-type strategies (2Retry, 3RB,
  8RetryRB, and 9RBRetry) can provide good RTT
  performance in the normal environment, however,
  their performances are not so good in the faulty
  environment.

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4. Experiments
3. Determine the optimal number of replicas.

• Two replicas are enough to provide high
  availability in the normal Internet environment,
  while three replicas are needed to ensure high
  availability in the 5 faulty Internet
  environment.

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5. Conclusion and future work

• Conclusion
• WS-DREAM
• Reliability assessment of individual Web
  services.
• Performance assessment of fault tolerance
  replication strategies.
• Experiment
• More than 1,000,000 test plans.
• Users from five locations.
• Web Services located in six countries.
• Future work
• Assessment of stateful Web services.
• Enhancement of system feature in facilitating
  user test case contributions

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WS-DREAM A Distributed Reliability Assessment
Mechanism for Web Services
Zibin Zheng, Michael R. LyuDepartment of
Computer Science EngineeringThe Chinese
University of Hong KongHong Kong, China
DSN 2008, Anchorage, Alaska, USA, 25 June, 2008