Distribuerade system - VT2001 Distribuerade system - VT2001 Jerry Eriksson Jerry Eriksson Contests Contests ä Introduction to DS Introduction to DS ä Schedule Schedule ä Litterature Litterature ä Laboration Laboration Defining DS Defining DS ä Network computers that communicate and Network computers that communicate and coordinate their actions only by passing coordinate their actions only by passing messages messages ä Consequences Consequences ä Concurrency Concurrency ä No global clock No global clock ä Independent failure Independent failure 1
Examples of DS; Internet Examples of DS; Internet intranet � � ISP � � backbone satellite link desktop computer: server: network link: Intranet Intranet Desktop email server computers print and other servers Local area Web server network email server print File server other servers the rest of the Internet router/firewall Mobile computing Mobile computing Internet WAP Host intranet Home intranet Wireless LAN gateway Mobile phone Printer Laptop Host site Camera 2
Litterature Litterature ä Distributed systems;concepts and design Distributed systems;concepts and design ä Secrets and lies Secrets and lies ä Some (just a few) articles Some (just a few) articles Schedule Schedule ä Foundations Foundations ä Focus on Focus on ä Middleware Middleware ä security security ä programming programming ä Distributed algorithms Distributed algorithms ä algorithms algorithms ä Shared data Shared data ä Start to work at once; Start to work at once; ä Multimedia system Multimedia system This is a D-cource !!! This is a D-cource !!! Laboration Laboration ä Only one lab. Rather big. Only one lab. Rather big. ä Groups of three. Groups of three. ä Requirement specification (High level) Requirement specification (High level) ä Up to you to design, implement and test. Up to you to design, implement and test. ä Weekly report of progess. Weekly report of progess. ä A lot of hard work, I guess. Hopefully, most A lot of hard work, I guess. Hopefully, most valueable when applying for job. valueable when applying for job. 3
People People ä Jerry Eriksson Jerry Eriksson ä Jonny Pettersson Jonny Pettersson ä Amanuens Amanuens ä Erik Lindström, guest lecturer Erik Lindström, guest lecturer My lectures My lectures ä Follow the book structure Follow the book structure ä self-study fully possible self-study fully possible ä (Not true for multimedia) (Not true for multimedia) ä Today chapter 1-3 Today chapter 1-3 Resource sharing; the web Resource sharing; the web http://www.google.comlsearch?q=kindberg www.google.com Browsers Web servers Internet www.cdk3.net http://www.cdk3.net/ www.w3c.org http://www.w3c.org/Protocols/Activity.html File system of Protocols www.w3c.org Activity.html 4
Challenges Challenges ä Heterogeneity Heterogeneity ä Opennes Opennes ä Security Security ä Scalability Scalability ä Faliure handling Faliure handling ä Concurrency Concurrency ä Transparency Transparency Heterogeneity Heterogeneity ä applies to applies to ä Middleware - software Middleware - software layer that provides layer that provides ä networks networks programming programming ä computer hardware computer hardware abstraction abstraction ä operating systems operating systems ä Mobile code - code Mobile code - code ä programming programming languages languages that be sent from one that be sent from one ä implementations by implementations by computer to another. computer to another. different developers different developers Java applets Java applets Openness Openness ä Extended and re- Extended and re- ä Open systems; Open systems; implemented implemented ä Key interafces are Key interafces are published published ä Very important in the Very important in the ä Open distributed Open distributed industry industry systems can be systems can be ä RFC (requests for RFC (requests for ä constructed from constructed from comments) comments) hetergenous hardware hetergenous hardware ä You’ll use it in your You’ll use it in your and software. and software. work. In this course. work. In this course. And probably in the And probably in the rest of your life rest of your life 5
Scalability Scalability ä Controlling the cost of physical resourses Controlling the cost of physical resourses ä Controlling the performance loss Controlling the performance loss ä Preventing software resourse running out Preventing software resourse running out ä Avoiding performance bottlenecks Avoiding performance bottlenecks Date Web servers Computers 188 0 1979, Dec. 1989, July 130,000 0 1999, July 56,218,000 5,560,866 Scalability Scalability Date Computers Web servers Percentage 1,776,000 130 0.008 1993, July 1995, July 6,642,000 23,500 0.4 1997, July 19,540,000 1,203,096 6 1999, July 56,218,000 6,598,697 12 Failure handling Failure handling ä Techniques for dealing with failures Techniques for dealing with failures ä Detecting failures Detecting failures ä Masking failures Masking failures ä Tolerating failures Tolerating failures ä Recovery from failures Recovery from failures ä Redundancy Redundancy 6
Transparency Transparency Access transparency : enables local and remote resources to be accessed using identical operations. Location transparency : enables resources to be accessed without knowledge of their location. Concurrency transparency : enables several processes to operate concurrently using shared resources without interference between them. Replication transparency : enables multiple instances of resources to be used to increase reliability and performance without knowledge of the replicas by users or application programmers. Failure transparency : enables the concealment of faults, allowing users and application programs to complete their tasks despite the failure of hardware or software components. Mobility transparency : allows the movement of resources and clients within a system without affecting the operation of users or programs. Performance transparency : allows the system to be reconfigured to improve performance as loads vary. Scaling transparency : allows the system and applications to expand in scale without change to the system structure or the application algorithms. 2. System Models 2. System Models ä Architectural models Architectural models ä Fundamental models Fundamental models ä Concerned with the Concerned with the ä Concerned with mode Concerned with mode placements of its parts placements of its parts formal description of formal description of and the relationships and the relationships the properties that are the properties that are between them. between them. common in architetural common in architetural models models ä Examples Examples ä Models Models ä Client-server Client-server ä peer-peer peer-peer ä Interaction model Interaction model ä Failure model Failure model ä Security model Security model Software and hardware layers Software and hardware layers Applications, services Middleware Operating system Platform Computer and network hardware 7
Platform and middleware Platform and middleware ä Platform Platform ä Middleware Middleware Client-server Client-server Client Server invocation invocation result result Server Client Key: Process: Computer: Multiple - servers Multiple - servers Service Server Client Server Client Server 8
Web proxy server Web proxy server Web Client server Proxy server Web Client server Peer processes Peer processes Application Application Coordination Coordination code code Application Coordination code Mobile code - web applets Mobile code - web applets a) client request results in the downloading of applet code Web Client server Applet code b) client interacts with the applet Web Client Applet server 9
Thin clients Thin clients Compute server Network computer or PC Application Thin network Process Client Mobile devices and spontaneous Mobile devices and spontaneous networking networking Music service Alarm gateway service Internet Hotel wireless network Discovery service Camera TV/PC Guests Laptop PDA devices Key features and other issues Key features and other issues ä Easy connection to a local network Easy connection to a local network ä Easy integration with local services Easy integration with local services ä Other issues Other issues ä Limited connectivity Limited connectivity ä Security and privacy Security and privacy ä Discovery services Discovery services ä Registration. Lookup services Registration. Lookup services 10 10
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