Dynamic Load Balancing on Web-server Systems - PowerPoint PPT Presentation

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Dynamic Load Balancing on Web-server Systems

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Dynamic Load Balancing on Web-server Systems

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  1. Dynamic Load Balancing on Web-server Systems Valeria Cardellini, Michele Colajanni, and Philip S. Yu Presented by Sui-Yu Wang

  2. Distributed Web-server System • Consisting of multiple Web-server hosts, distributed on LANs and WANs • Spread incoming requests among these servers • Each server can respond to any request • Successful load-balancing approaches make the distributed system appear as a single host

  3. Distributed Web-server Architectures • Client-based • Web clients • Client-side proxies • Web-server based • DNS-based • Dispatcher-based • Server-based

  4. DNS-based approach • Architecture transparency • DNS has limited control on requests reaching the Web cluster • TTL • Scheduling algorithms • Constant TTL • Adaptive TTL

  5. Scheduling algorithms • Constant TTL algorithms • System-stateless algorithms • Round-Robin DNS • Server-state-based algorithms • Client-state-based algorithms • Hidden load weight • Multitier round-robin policy • Consider relative server-to-client topology and client-to-server link latency • Network proximity information, round trip delays • Server-and client-state-based algorithms

  6. Scheduling algorithms • Adaptive TTL algorithms • Select server similar to the hidden load weight algorithms • Assign appropriate TTL • Can scale from LANs to WANs

  7. Dispatcher-based Approach • Centralized request scheduling • Packet rewriting • Single-rewriting • Double-rewriting • Packet forwarding • HTTP redirection

  8. Packet single-rewriting

  9. Packet double-rewriting

  10. Packet forwarding • Network Dispatcher • Works with LANs and WANs • Client and server transparent • ONE-IP Address • Routing-based dispatching • Broadcast-based dispatching • No dynamic load-balancing based on server load

  11. HTTP redirection • Centralized dispatcher • Does not require modification of packet IP address • Server-state based dispatching • Location-based dispatching

  12. Server-based approach • Two-level dispatching • No centralized dispatching • HTTP redirection • Packet redirection • Static routing • Load-balancing

  13. Comparison of different approaches

  14. Performance evaluation • Exponential model: the number of page requests per session and the time between two page requests from the same client were assumed to be exponentially distributed

  15. Performance evaluation • Client load variability is represented by some heavy-tailed function