Reliable Web Services by Fault Tolerant Techniques: Methodology, Experiment, Modeling and Evaluation

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Reliable Web Services by Fault Tolerant
Techniques Methodology, Experiment, Modeling and
Evaluation

• Term Presentation
• Presented by Pat Chan
• 3 May 2006

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Outline

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

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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.

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Reliability

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

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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)

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Web Services
UDDI
Internet
WSDL
WSDL
HTTP/SOAP
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Web Services Architecture
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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.
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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.

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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.

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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

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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

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Failure Response Stages of Web Services

• Fault confinement
• Fault detection
• Diagnosis
• Fail-over
• Reconfiguration
• Recovery
• Restart
• Repair
• Reintegration

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(No Transcript)
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Propose Paradigm
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Work Flow of the Replication Manager
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Road Map for Experiment Research

• Redundancy in time
• Redundancy in space
• Sequentially
• Parallel
• Majority voting using N modular redundancy
• Diversified version of different services

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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.

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Summary of the Experiments
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Parameters of the Experiments
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Experimental Results
Experiments over 360 hour period (43200 reqs) Normal Resource Problem Entry Point Failure Network Level Fault Injection
Exp 0 4928 6130 6492 5324
Exp 1 2210 2327 2658 2289
Exp 2 2561 3160 3323 5211
Exp 3 1324 1711 1658 5258
Exp 4 1089 1148 1325 2210
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
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Number of Failure When the Server is Normal
Situation
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Number of Failure When the Server is Busy
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Number of Failure When the Server Reboots
Periodically
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Network Level Fault Injection
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Reliability of the System Over Time
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Reliability Model
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Reliability Model
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SHARPE
Reliability with different failure rate
Failure rate 0.005 0.05 0.01 0.02 0.03 0.04
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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.