1 Distribuerede systemer og sikkerhed – 4. februar 2002 From Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edition 3, © Addison-Wesley.

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1 1 Distribuerede systemer og sikkerhed – 4. februar 2002 From Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edition 3, © Addison-Wesley 2001 Presentation based on slides for the book: Slides modified by Jens B Jorgensen, University of Aarhus

2 2 Lærebøger og information zDistributed Systems – Concepts and Design, Coulouris, Dollimore, Kindberg. zData & Computer Communications, Stallings. zNoter om farvede Petri-net, CPN. zKursusinformation paa www.daimi.au.dk/dDist og nyhedsgruppe daimi.ddist.www.daimi.au.dk/dDist

3 3 Forelæsninger og øvelser zForelæsninger – i alt 3 timer pr. uge: ymandag 10-12, Aud. D2. ytorsdag 14-16, Aud. D2. zØvelser:  Hold 1: Onsdag 8-11, lokale 1-532-316.  Hold 2: Mandag 12-15, *** H2.28. ***  Hold 3: Torsdag 11-14, lokale 1-532-316.  Hold 4: Torsdag 11-14, lokale 1-521-228.  Hold 5: Onsdag 9-12, Kollokvium G4. zØvelser i uge (n+1) svarer til forelæsninger i uge n; øvelser første gang i uge 7, mandag 11. februar.

4 4 Bemanding zForelæser: Jens Bæk Jørgensen. zAdministrerende instruktor: Thomas Mailund. zInstruktorer: yLisa Wells. yThomas Ljungberg. yThomas Pedersen. yNN. yMM.

5 5 Forelæser z1991: Kandidat fra DAIMI. z1991-93: Systemudvikler hos Meta Software Corporation, Boston. z1997: PhD fra DAIMI; emne: farvede Petri-net. z1997-01: Systemudvikler hos Systematic Software Engineering, Århus. z2001-?: Adjunkt ved DAIMI.

6 6 Kursusplan zEmner yDistributed Systems indtil påske. yNetworks fra påske til semesterafslutning. yLøbende brug af farvede Petri-net, Coloured Petri Nets (CPN) zKurset er omfangsrigt – prioriter overblik og bredde. zSkim stof inden forelæsning. zFølg med på www.daimi.au.dk/dDist og nyhedsgruppe daimi.ddist.www.daimi.au.dk/dDist

7 7 Kursusformål zCoulouris: “Convey insight into, and knowledge of, the principles and practice underlying the design of distributed systems, both Internet-based and otherwise.” zNøgleord: systemmodeller (fx client-server), interprocess communication (fx TCP), RPC/RMI, transactions, concurrency control. zStallings: “Provide a unified overview of the broad field of data and computer communications.” zNøgleord: WAN, LAN, internets, protocols, security.

8 8 Chapter 1: Characterization of Distributed Systems From Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edition 3, © Addison-Wesley 2001

9 9 Distributed systems zDefinition: A distributed system is one in which components located at networked computers communicate and coordinate their actions only by passing messages. zPrimary purpose: Sharing of resources, e.g., disks, printers, files, and databases. zEksemples: yDAIMI’s IT infrastrukture. yThe Internet. yÅrhus Amt’s elektronic patient record. yAmanda. y…

10 10 Distributed systems – main characteristics zConcurrency: Parallel activities, shared resources, coordination. zNo global clock: No common notion of time, timing problems. zIndependent failures: Network, software, hardware, undiscovered errors. yLamport’s definition of a distributed system: “One in which the failure of a computer you didn't even know existed can render your own computer unusable”.

11 11 The Internet (extract) Standardised protocols; Services: www, email, ftp,..

12 12 The Internet – size Date Computers Web servers 1979, Dec. 1880 1989, July130,0000 1999, July56,218,0005,560,866

13 13 An intranet and other servers other servers print Local area network email server the Internet Separately administered, local security policies

14 14 Mobile, ubiquitous, and pervasive computing Example: Pervasive healthcare

15 15 Client-server communication zService: Distinct part of a computer system that manages a collection of related resources and presents their functionality to users and applications. zServer: A running program (a process) on a networked computer that accepts requests from programs running on other computers to perform a service and respond appropriately. zClient: User of a server.

16 16 World Wide Web Internet Browsers Web servers www.google.com www.cdk3.net www.w3c.org Protocols Activity.html http://www.w3c.org/Protocols/Activity.html http://www.google.com/search?q=kindberg http://www.cdk3.net/ File system of www.w3c.org Server DNS (Domain Name Service) name Pathname on server Arguments

17 17 Distributed systems design issues zHeterogeneity zOpenness zSecurity zScalability zFailure handling zConcurrency zTransparancies (incl. access and location transparancies)

18 18 Distributed systems – summary zDefinition and characterisation of distributed systems. zExamples, e.g., the Internet. zClient/server communication. zWorld Wide Web. zDesign issues: Heterogeneity, openness, security, scalability, failure handling, concurrency, transparancy.