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A Throttling Layer-7 Web Switch James Furness

A Throttling Layer-7 Web Switch James Furness. Motivation & Goals Specification & Design Design detail Demonstration Conclusion. Project Goals. Present a heterogeneous pool of web servers as a single virtual server Maximise availability and response times by throttling

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A Throttling Layer-7 Web Switch James Furness

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  1. A Throttling Layer-7 Web SwitchJames Furness

  2. Motivation & Goals • Specification & Design • Design detail • Demonstration • Conclusion

  3. Project Goals • Present a heterogeneous pool of web servers as a single virtual server • Maximise availability and response times by throttling • Balance load between servers in pool • Design as a modular framework to maximise extensibility A Throttling Layer-7 Web Switch

  4. Source: Netcraft Motivation • Rapid growth in usage of the world-wide web • Rapid growth in bandwidth available to end user • Users expect timely responses A Throttling Layer-7 Web Switch

  5. Motivation • Web sites must continue to provide timely responses to all users under high demand • Options: • Slow incoming request rate • Increase capacity/parallelism • Increase throughput A Throttling Layer-7 Web Switch

  6. Motivation & Goals • Specification & Design • Design detail • Demonstration • Conclusion

  7. System Specification • Cluster-based Web system • Layer-7 switching • Virtual File System allows multiple versions of content to be provided on multiple backend servers • Aim: Degrade responses from highest quality as load increases A Throttling Layer-7 Web Switch

  8. System Monitors Control Layer Architecture • VFS performs virtual to physical mapping and stores Path monitoring data • Policy engine prioritises alternative versions of content according to load • Control Layer interface provides façade • System monitors and dispatching algorithm user-specified Control Layer Policy Engine Configuration Module Virtual File System Virtual Path Mapper Monitoring Data Dispatching Algorithm Control Layer Interface Routing Layer Callbacks A Throttling Layer-7 Web Switch

  9. System Architecture • Two-layer approach • Separate routing and the logic making routing decisions • Abstracts routing method from Control Layer • Control Layer can be retro-fitted to any web switch • Routing Layer is a minimally modified proxy server Web Switch Control Layer Virtual to Physical Translation Load Balancing 3. Physical Paths 4. Ordered Physical Paths 2. Virtual Path Routing Layer Decode Request Rewrite Request Forward Response 5. Rewritten Request 1. Request User 7. Response 6. Response Pool Servers A Throttling Layer-7 Web Switch

  10. System Architecture • Scalable Content-blind load balancer (Layer-4) Web Switches (Layer-7) Server pool • Portable (Java) A Throttling Layer-7 Web Switch

  11. Motivation & Goals • Specification & Design • Design detail • Demonstration • Conclusion

  12. Default Policy • Carry alternative pages of varying bandwidth/load • Switch between versions to prevent flooding of outbound bandwidth and to reduce response times of dynamic pages under high load • Prioritise physical paths using: • Monitoring data • System data • Host data • Path data • Metadata • Load Weighting • Bandwidth Weighting A Throttling Layer-7 Web Switch

  13. Default Monitoring Data • Collect system bandwidth usage • Collect physical path response times • Response time provides a platform independent measure of end-to-end system performance • Calibrate system by including target response time average + standard deviation in metadata • Normalise monitored response times using metadata • Collect average of recent normalised response times for path and also for all paths on host using sliding window A Throttling Layer-7 Web Switch

  14. Default Dispatching Algorithm • Throttle bandwidth back as connection maximum is approached • Favour paths averaging < 1 s.d • Reward/punish dynamic pages more than static pages A Throttling Layer-7 Web Switch

  15. Default Dispatching Algorithm • Secondary criteria: • Favour hosts with low average standardised response time • Favour hosts with least active connections A Throttling Layer-7 Web Switch

  16. Experimental Results A Throttling Layer-7 Web Switch

  17. Experimental Results A Throttling Layer-7 Web Switch

  18. Motivation & Goals • Specification & Design • Design detail • Demonstration • Conclusion

  19. Motivation & Goals • Specification & Design • Design detail • Demonstration • Conclusion

  20. Conclusion • System designed & implemented conforming to goals • Scalable • Testing proves an increase in throughput compared to a system without throttling A Throttling Layer-7 Web Switch

  21. Questions?

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