1. Wide Web Load Balancing Algorithm Design Yingfang Zhang

2. Outline of the Talk Introduction to wide web load balancing problem and related works Load balancing algorithm design and load balancing algorithms Sequence chart of simulation program Traffic characteristics of web servers and clients Test plan Simulation results Conclusion and future directions

3. Introduction Load Balancing Problem Web Server 1 Web Server N Web system plays an essential role in providing and retrieving information. Cause web server to the overload and longer response time Duplicated web system is widely used today with purpose to spread the client’s requests and shorten the response time Key problem is how to allocate the requests efficiently to shorten the response time Client Request Which Web Server to Choose? ? ?

4. Related Works on Web Systems NCSA Scalable Web Server…. CISCO Distributed Director… GIT Feo et al, Dynamic Server Selection,…

5. NCSA Scalable Web Server Advantage: Used in LAN local network. Because it ignores the path information, e.g., distance, hop count, bandwidth…, so it is simple, typically, it uses Round-Robin strategy. Disadvantages: 1. Just Balancing web servers that are located at same domain. 2. Just Control parts of the requests due to name caching in the intermediate name server.

6. CISCO Distributed Director.

7. Advantage: 1. Balancing geographical separate servers. Disadvantage: 1. Because of centralizing the requests, become bottleneck.

8. GIT Feo et al,Dynamic Server Selection

9. Advantage: 1. User has the multiple choices to select the web server based on the performance of web server. Disadvantage: 1. Result in congestion due to client’s rushing to the lightly loaded servers

10. Load Balancing Algorithm Advantages: 1. Combine path information: Distance. Hop count. Bandwidth. Dynamic traffic delay. with web information : Processing power. Number of pending requests. Size of pending requests. Web server count. to guide allocating requests, therefore, load balancing algorithms can be used in wide web system. Because we combine static and dynamic information, The load balancing algorithms eliminate the congestion that happens at Dynamic server selection.

11. 2. Design LBA, It can control all requests comparing to DNS, and avoid the bottleneck that is in Cisco Distributed Director. Load Balancing Algorithm

12. Web Components and Their Interaction

13. Two Metrics 1. Current Load L 1,t /S 1 = L 2,t /S 2 = L 3,t /S 3 … = L k,t /S k The goal is to make the loads even among the web servers 2. Average Response Time (ART) ART load-balancing status = min{ART} The goal is to shorten the response time

14. Factors That Affect Load Balancing The size of request. The web processing power. The number of pending requests at the web server. The size of pending requests at the web server. The distance of the path between clients and web servers. The available bandwidth along the path. The hop count along the path. The traffic status. The number of the web servers. The number of the clients. The number of the requests

15. Load Balancing Algorithm Design Concern two processing time of the requests in load balancing algorithms: 1. Time from the client to web server. It Includes time: Transmission delay Queueing delay 2. Time stay at web server. It Includes time: Queueing delay at web server Processing time at web server Idea  Balancing those times. Finally the load balancing algorithm should try to shorten the end-to-end response time of the requests.

16. Load Balancing Algorithm Design Factors related to first portion of the time are the path information,e.g.,distance, hop count, bandwidth, dynamic traffic delay. Factors related to second portion of the time are the web information,e.g., web processing power, number of pending requests.

17. Load Balancing Algorithm I 1. LBA-I: Use all static information Selected web server i = Min{distance/bandwidth + loads of web server i / process power of web server i} Use the ratio of distance to bandwidth to measure the path, Use the ratio of web server loads to processing power to measure the web status. There are two variations of the algorithms: LBA-I-1: Add hop count LBA-I-2: Just concern web server status, ignore the path information.

18. Load Balancing Algorithm II LBA-II: LBAs communicate with each other. When a LBA makes an assignment decision, It passes this info to other LBAs, other LBAs update their assignment table. Advantage: Improve the estimated precision of loads of web server. Disadvantage: Generate heavy communication overhead and take away available bandwidth for web access. A variation of the algorithm LBA-II-1. Just pass the assignment info to neighboring LBAs Advantage: Reduce communication overhead. Disadvantage: Decrease the estimated precision of web server loads.

19. Load Balancing Algorithm III Using static information to measure the path traffic in LBA-I and LBA-II. LBA-III: Using dynamic path information. Periodically send probing packets to probe path bandwidth. Advantage: Improve the estimated precision of the path traffic. Disadvantages: 1. Generate heavy communication overhead, reduce available bandwidth. 2. The performance of the algorithm depends on the probing path message period.

20. Load Balancing Algorithm IV Using the number of the assignment requests to measure the web server loads in LBA-I, LBA-II and LBA-III. LBA-IV: Using the size of pending request information to measure the web server load status. Web servers periodically send the this information to LBAs Advantage: Improve the estimated precision of web server loads. Disadvantages: 1. Generate heavy communication overhead, reduce available bandwidth. 2. The performance of the algorithm depends on web server reporting period.

21. There are two variations of the algorithms 1. LBA-IV(E): Long period, during a period interval, using first order random walking model to estimate the load of the web server Advantage: Reduce the communication overhead. Disadvantage: Decrease the estimated precision of loads at web servers 2. LBA-IV(Tc): Overload alarming threshold. Web servers send asynchronous overload alarming message to LBAs. Advantage: Reduce the communication overhead. Load Balancing Algorithm IV

22. Simulation Program Design 1. Using discrete event simulation. 2. There are 4 types of nodes: Web Server, LBA, Router, Client 3. There are 6 types of the packets: Request packet sent by client Document packet sent by web server Path Probing message sent by LBA Current-load-report message sent by web server Overload-alarming message sent by web server Load balancing coordination message sent by LBA

23. Sequence Chart Of Simulation Program

24. Web Server and Client Traffic Characteristics Log Files of Five Web Server are analyzed: 1. Department wide server at UCCS run on an Alpha workstation owl.uccs.edu. 2. Campus wide server at UCCS run on an Alpha workstation www.uccs.edu. 3. ClarkNet WWW server, which is a full Internet access provider for the Metro Baltimore-Washington DC area. 4. EPA WWW server located at Research Triangle Park, NC. 5. BU-Web-Client in the Boston University Computer Science Department. Analyzing the statistic characteristics of the workload of the web servers and clients. Comparing those characteristics with other reports

25. Characteristics of Document Type Most frequently requested by the clients are image and HTML type, which account over 80%of all requested type.

26. Characteristics of Document Size Most document size requested by the clients is 1 ~ 5 KB

27. Characteristics of Request Time Interval Most time interval of the requests is less than 1 sec

28. Test Plan There are the factors affecting performance of algorithms 1. Network topology 2. Number of the request 3. Request time interval 4. Bandwidth We will change those parameters to test the performance of the algorithms. We will statistics the following Data: 1. Average response time 2. Web queueing delay time 3. Router queueing delay time 4. Transmission delay time 5. Propagation delay time 6. Processing time 7. Various communication overhead

29. Performance of Load Balancing Algorithms Distribution of request time interval as previous figure. Distribution of document size as previous figure. Range of the request count from 800 to 10000 Average Bandwidth is 5 Mbps New-Jersey Network with 116 nodes and 22 links Transmission delay ( 90%) dominates the response time

30. Performance of Load Balancing Algorithms Distribution of request time interval as previous figure Distribution of document size as previous figure Range of the request count from 800 to 10000 Average bandwidth is 5 Mbps r50 Network with 890 nodes and 217 links Transmission delay ( 80%) dominates the response time

31. Performance of Load Balancing Algorithm

32. Algorithm LBA-I

33. Performance of Load Balancing Algorithm Algorithm LBA-I-1

34. Performance of Load Balancing Algorithm Algorithm LBA-I-2

35. Performance of Load Balancing Algorithm Algorithm RR

36. Performance of Load Balancing Algorithm Algorithm LBA-II(I)

37. Performance of Load Balancing Algorithm Algorithm Random

38. Performance of Load Balancing Algorithm Algorithm LBA-II(I-2)

39. Performance of Load Balancing Algorithm Algorithm LBA-III

40. Performance of Load Balancing Algorithm Algorithm LBA-IV(3)

41. Performance of Load Balancing Algorithms We change the request interval time Comparing to previous request interval distribution, above distribution is 10000 times faster

42. Performance of Load Balancing Algorithms Distribution of request time interval as above figure. Distribution of document size as previous figure. Range of the request count from 800 to 3000. New-Jersey Network with 116 nodes and 22 links Web queuing delay ( 80%) dominates the response time

43. Performance of Load Balancing Algorithms

44. Performance of Load Balancing Algorithm Algorithm LBA-I

45. Performance of Load Balancing Algorithm Algorithm LBA-I-1

46. Performance of Load Balancing Algorithms Algorithm LBA-I-2

47. Performance of Load Balancing Algorithm Algorithm RR

48. Performance of Load Balancing Algorithm Algorithm Random

49. Performance of Load Balancing Algorithm Algorithm LBA-II(I)

50. Performance of Load Balancing Algorithm Algorithm LBA-II(I-2)

51. Performance of Load Balancing Algorithm Algorithm LBA-IV

52. Conclusions 1. Algorithm LBA-I and LBA-I-1 have the better performance when the transmission delay dominates the response time. They are independent of any period and do not generate any overhead messages. 2. Algorithm LBA-II have the better performance when the web queueing delay dominates the response time. It generates very heavy overhead messages and is independent of reporting period. 3. Algorithm LBA-III have the worse performance in both case-- transmission delay dominates the response time and web queueing delay dominates response time. It generates very heavy overhead messages and is dependent on reporting period. 4. Algorithm LBA-IV has the better performance when the web queuing delay dominates the response time. It generates overhead messages and is dependent on reporting period.

53. Network Design Issues If the transmission delay dominates the response time, We have following suggestions for network design: 1. Reduce document size. 2. Choose proper ratio of web servers and clients 3. Choose proper process power of web servers 4. Choose proper location of web servers

54. Future Directions 1. Using real and larger networks to test the proposed load balancing algorithms 2. Investigate algorithm performance under heavy web server load. 3. Investigate aggregate server/LBA reporting and impact of reporting frequencies. 4. Implement load balancing algorithms in a prototype.