網際網路的普及與WWW的快速崛起，正宣告了另一波的資訊革命與一個嶄新時代的來臨，在這個堪稱第四波工業革命的浪潮中，如何運作一個能提供良好服務品質的高效能伺服器系統，來對外交換資訊、提供各類服務甚或是進行商業交易，已成為一個備受各方關注的課題。然而，由於網際網路快速且驚人的成長，所伴隨而來的網路壅塞、伺服器過度負載、資料擷取時間過長等問題，正成為相關網路服務發展的一大隱憂。因此，有越來越多的網路服務提供業者利用分散式系統的觀念來建構他們的伺服器系統。這類的分散式伺服器系統雖然具有較佳的價格�性能比、可擴充性，較好的容錯能力等優點，但是現有的分散式伺服器架構並不足以解決現今往往服務所面臨的種種問題。
本論文即是在分散式伺服器系統的概念上發展各項核心技術，並將其結合成為一個整合性的系統，以期能夠將一群性能互異的電腦整合成一個能應付現今網路世界中各項挑戰的高效能、智慧型伺服器系統。本論文所發展的系統可以分成兩大部分:高智能負載平衡器與分散式伺服器管理系統。負載平衡器之目的在於將使用者需求公平且適切地分配到各個機器上去，其中包含負載平衡、滿足交易完整性、提供分級服務、服務品質確保、系統錯誤偵測與排除以及提供外界使用者單一系統的假象等機制。
分散式伺服器管理系統則可視同為分散式伺服器架構的”數位神經系統”。具體來說，就如同神經系統的兩大功能:指揮與感知，如果管理者想要針對整個系統執行某些系統管理工作時，他只需下達一次系統管理命令，管理系統將能指揮系統中的各個節點共同協力完成該項系統管理工作。另一方面，面對瞬息萬變的網路狀況，管理系統在平時將自動維護整個系統，當它感知到系統發生某些狀況時，能夠迅速的做出反應、重組系統架構，或是與前端的負載平衡器搭配，自動的調適整個伺服器系統，使其能一直維持在高效能的穩定狀態。

The Internet is increasingly being used as basic infrastructure for a variety of services. A high-performance server system is the key to the success of all these Internet services. However, the explosive growth of Internet has resulted in heavy demands being placed on Internet servers and has raised great concerns in terms of performance, scalability and availability of the associated services. A monolithic server hosting a service is usually not sufficient to handle these challenges. Distributed server architecture, consisting of multiple heterogeneous computers that appears as a single high performance system, has proven a successful and cost effective alternative to meet these challenges. Consequently, more and more Internet service providers run their service on a cluster of servers, and this trend is accelerating.
The distributed server architecture is only an insufficient answer to the challenges faced by Internet service providers today. This thesis presents an integrated system for supporting scalable and highly reliable Internet services on the distributed server architecture. This system is composed consists of two major parts: Server Load Balancer and Distributed Server management System. The server load balancer can intelligently route the incoming requests to the appropriate server node. The Java-based management system can relieve administrator‘s burden on managing such a distributed server system. With these mechanisms, we can provide an integrated system to consolidate a group of heterogeneous computers to be a powerful, adaptive, reliable Internet server system.

1. INTRODUCTION 1
1.1 WORKLOAD CHARACTERISTICS 2
1.2 DESIGN ISSUES 4
1.3 SYSTEM OVERVIEW 6
1.4 THESIS ROADMAP 7
2. BACKGROUND 9
2.1 WORLD WIDE WEB 9
2.2 RELATED WORK 12
2.2.1 Clustering for Internet Services 12
2.2.2 Request Routing Mechanism 12
2.2.3 Web Performance 15
2.2.4 Load Balancing 15
3. CONTENT-AWARE DISTRIBUTOR 17
3.1 MOTIVATION 17
3.1.1 Session Integrity 17
3.1.2 Sophisticated Load Balancing 18
3.1.3 Content Deployment 18
3.1.4 Differentiated Web Services 19
3.1.5 Summary 19
3.2 DESIGN AND OPERATION OF THE CONTENT-AWARE ROUTING MECHANISM 20
3.2.1 Connection setup 22
3.2.2 Transmitting the HTTP Request 22
3.2.3 Server Response and Subsequent Requests 23
3.2.4 Connection Reuse or Termination 24
3.3 IMPLEMENTATION 26
3.3.1 Mapping Table 26
3.3.2 Connection Reuse 27
3.3.3 Connection Management 29
3.3.4 URL Table 29
3.3.5 Implementation Status 31
3.4 COMPETING APPROACHES 31
3.4.1 TCP State Migration 31
3.4.2 TCP Splicing 32
3.4.3 Comparison 34
4. MANAGEMENT SYSTEM FRAMEWORK 36
4.1 MOTIVATION 36
4.2 DESIGN ISSUES 37
4.3 IMPLEMENTATION 39
4.3.1 Control Interface 39
4.3.2 Controller 40
4.3.3 Broker 41
4.3.3.1 Agent Thread 41
4.3.3.2 Monitor Thread 42
4.3.4 Agent 43
4.3.5 Remote console 44
4.4 DISCUSSION 47
5. CONTENT ENGINEERING 49
5.1 MOTIVATION 49
5.1.1 Content Placement 50
5.1.2 Content Management 51
5.2 CONTENT MANAGEMENT 52
5.3 CONTENT PLACEMENT 55
5.3.1 URL Formalization 55
5.3.2 304 Effect 57
5.3.3 Discussion 57
5.4.4 System Support for the URL Formalization 58
5.6 DISCUSSION 59
6. SYSTEM RELIABILITY 61
6.1 ANALYSIS 61
6.2 REQUEST FAIL-OVER 62
6.2.1 Requests for Static Content 63
6.2.2 Requests for Dynamic Content 64
6.2.3 Stateful Request 65
6.3 SYSTEM ROBUST 68
6.4 SUMMARY 69
7. SYSTEM EVALUATION 71
7.1 MEASUREMENT SETUP 71
7.1.1 Sever Cluster 71
7.1.2 Load Generator 72
7.1.3 Workload 72
7.2 PERFORMANCE OF CONTENT-AWARE ROUTING MECHANISM 73
7.2.1 Overhead of Content-Aware Routing 73
7.2.2 Benefits of the Content-Aware Routing 73
7.2.3 Lessons Learned 75
7.3 PERFORMANCE OF CONTENT PLACEMENT SCHEME 75
7.4 SERVICE RELIABILITY 78
7.4.1 Fail-over Time 78
7.4.1.1 Request for Static Content 79
7.4.1.2 Request for Dynamic Content 80
7.4.1.3 Session-based Requests 81
7.4.2 Overhead and Scalability 81
7.4.3 A Long-running Test 83
7.5 BENEFITS OF URL FORMALIZATION 84
8. CONCLUSION AND FUTURE WORK 87
APPENDIX A: AGENTCONTEXT 89
APPENDIX B: WORKLOAD 91
REFERENCE: 92

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