Making Services Fault Tolerant

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Making Services Fault Tolerant

• Pat Chan
• Department of Computer Science and Engineering
• The Chinese University of Hong Kong
• 27 June 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
• Future Directions

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Introduction

• Service-oriented computing is becoming a reality.
• Service-oriented Architectures (SOA) are based on
  a simple model of roles.
• The problems of service dependability, security
  and timeliness are becoming critical.
• We propose experimental settings and offer a
  roadmap to dependable Web services.

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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
• Redundant 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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Proposed 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
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 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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Reliability of the system over time
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Reliability Model
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Reliability Model Parameters
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Outcome (SHARPE)
Reliability of the proposed system
Failure Rate 0.228 0.114 0.057
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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.
• N-Version Programming may finally become
  commercially viable in service environment.

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Future Directions

• Make experiments comprehensive range of service
  arrival rates or distributions, failure rates,
  polling frequency, etc.
• 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.

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Future Directions

• Modeling the Web Service behavior
• The behavior of the We Services can be studied.
• Modeling the failure
• Study the failure model of Web Service.