2. Distributed Systems Distributed systems—principles and paradigms, Tanenbaum Distributed systems—concepts and design, George Coulouris 分布式系统, 李西宁, 科学出版社, 2006

3. = Supercomputer

4. 1. Introduction (Evolution) 2. Some system models 3. Communication in distributed systems 4. Distributed programming 5. Distributed OS: Processes, Naming, Synchronization 6. Distributed object-based systems: CORBA, DCOM 7. Web services 8. DDM: Consistency, replication, concurrency (DNS) 9. Peer-to-peer computing Table of Contents

5. 10. Grid 11. Fault tolerance 12. Security

6. 1. Introduction

7. 1.1 Introduction 1. What is a distributed system? (P2) A distributed system is a collection of indepen- dent computers that appears to its users as a single coherent system. A distributed computing system consists of multiple autonomous computers (or processors) that do not share primary memory, but cooperate by sending message over a communication network.

8. Kmap3 Kmap2Kmap4 Kmap5 Kmap1 1 10 20 11 2130 4150 31 40 Cm * Carnegie Mellon University 1976

9. Now:Web service, Grid, P2P 1982 ZCZ LSI Nanjing University

10. Characteristics: multiple computers communication resource sharing decentralized parallel processing transparency independent failures

11. Transparency in a Distributed System Different forms of transparency in a distributed system. Hide whether a (software) resource is in memory or on disk Persistence Hide the failure and recovery of a resourceFailure Hide that a resource may be shared by several competitive users Concurrency Hide that a resource may be replicatedReplication Hide that a resource may be moved to another location while in use Relocation Hide that a resource may move to another locationMigration Hide where a resource is locatedLocation Hide differences in data representation and how a resource is accessed Access DescriptionTransparency P5

12. robustness maintenance extensibility (scalability) efficiency (performance/cost) people are distributed information is distributedDNS Disadvantages: network can cause problems security is a problem software is needed Advantages

13. About openness --- a goal 1) A open distributed system is a system that offers services according to standard rules. * resources sharing --- Web * parallel distributed computing (cooperative computing) --- communication Computer network --- protocols Distributed system --- IDL, XML, protocols P8

14. 2) Advantages interoperability portability P8

15. 2. Differences between network and D.S Early LANDistributed system Resource Location Cooperate Distance Now NetworkDistributed system private, shared shared, private transparentnot noyes small small or large resources sharing basis resources integration middleware

16. Network Operating System General structure of a network operating system. 1-19 Resource management?

17. Distributed Operating Systems General structure of a multicomputer operating system 1.14 P28

18. Motivation for Internet If one part of system is broken or destroyed, the other will continue to work. It is impossible to destroy something that has no headquarters, no leader and not just one machine doing all work. Internet 计算的第二波将受到不断扩展的分布式 计算构架的推动。 Internet 使分布式计算具有新的潜力, 人们对分 布式计算提出了新的要求 3. Is Internet a distributed system?

19. 4. Evolution 1) Distributed computer system Success: –Many concepts and techniques were proposed –Centralized computing distributed computing Failure : –The system was not accepted DOS

20. 2) Distributed System organized as middleware Note that the middleware layer extends over multiple machines. P3

21. Distributed Computing Environment CORBA DCE NOS1 DCE NOS2 DCE NOSi prog o obj Lang1Lang2Lang3 ORB NOS1 ORB NOS2 ORB NOS3

22. Success: –Distributed object technique and some products appeared. CORBA DCOM EJB/J2EE Result: promote the development of distributed application system. (develop and assemble distributed object) Issue : –not unify (not openness) Web services

23. Software agents An autonomous process capable of reacting to, and initiating changes in its environment, possibly in collaboration with users and other agents. To act on its own, to take initiative where appropriate 3) Distributed object technique combines AI technique P173

24. (a) Grid Infrastructure that facilitates controlled sharing of resources across organizational boundaries. – “ 网络 ” 实现了计算机硬件的连通, “Web” 实现了网页 连通 – “ 网格 ” 在应用层面实现所有资源的全面连通, 包括计算, 存储, 软件, 数据, 仪器设备 … Computational grid Data grid Earthquake 3) Wide-area distributed system

25. Grid Computing 网格计算就是基于网格的问题求解。 Use hardware & software facilities, that research institutes in the world have, to solve very complicated scientific research and computational problems.

26. (b) Web services -- distributed system combines WWW identified by URIs; accessible via standard Web protocols; capable of sending, receiving, and acting on XML based message; and capable of interacting with applications and programs that are not directly human-driven user interfaces Windows.NET or Java Tomcat  CORBA, DCOM, EJB

27. (c) Peer to peer system Computers operating as peers collaborate to achieve an end result without a central authority P2P computing has both technical and social components Napster --- share MP3 files

28. Hierarchy Distributed application system Distributed support system: middleware Grid, P2P, Web service Network OS, Internet LAN, WAN

29. provide universal service in a heterogeneous world. Communication Interoperability TCP/IP interface/XML/others Hete. OSHete. language Hete. networkHete. OS, net 5. Key issue

30. Software Concepts An overview between DOS (Distributed Operating Systems) NOS (Network Operating Systems) Middleware P36 Provide distribution transparency Additional layer atop of NOS implementing general-purpose services Middleware Offer local services to remote clients Loosely-coupled operating system for heterogeneous multicomputers (LAN and WAN) NOS Hide and manage hardware resources operating system for homogeneous multicomputers DOS Main GoalDescriptionSystem P23

31. Comparison between Systems A comparison between multiprocessor operating systems, multicomputer operating systems, network operating systems, and middleware based distributed systems. Open Closed Openness VariesYesModeratelyNoScalability Per node Global, distributed Global, central Resource management Model specific FilesMessages Shared memory Basis for communication NNN1 Number of copies of OS No Yes Same OS on all nodes HighLowHighVery High Degree of transparency Multicomp.Multiproc. Middleware- based OS Network OS Distributed OS Item P41

32. Clients and Servers General interaction between a client and a server. 1.25

33. Multitiered Architectures An example of a server acting as a client. 1-30

34. Multitiered Architectures Alternative client-server organizations (a) – (e). 1-29

35. Another architectures An example of horizontal distribution of a Web service. 1-31

36. Summary 1. Concepts 2. Evolution –local area ---> medium ---> Internet (wide area) –distributed OS --> middleware --> protocols, specifications 3. Multiprocessor system –Hardwarepurposes? Network; Distributed system; Parallel computer –Software NOS; Middleware, support systems…; DOS

37. Related magazines IEEE Transaction on Parallel and Distributed Systems http://computer.org/tpdstpds@computer.org Distributed Computing http://link.springer.de/comp/ http://link.springer-ny.com Journal of Parallel and Distributed Computing http://www.academicpress.com/jpdc home page http://www.idealibrary.compapers Internet Computing http://computer.org/internet/