Computer Science 425 Distributed Systems CS 425 / CSE 424 / ECE 428 Fall 2010Our First Aim in this Course was… (first lecture)….Can you name some examples of Distributed Systems?What is a Distributed System?FOLDOC definitionTextbook definitionsA working definition for usProblems we have Seen and Solved Since ThenProblems we have Seen and Solved in this ClassProblems we have Seen and Solved in this Class (2)Problems we have Seen and Solved in this Class (3)A range of Challenges for DesignersWhat we Have Learned Since ThenProblems we have Seen and Solved in this Class (and relation to other courses)Problems we have Seen and Solved in this Class (and relation to other courses)Slide 16CS525: Advanced Distributed Systems (taught by Indy)Questions?Slide 19Etc.Course EvaluationThank YouLecture 29-1Lecture 29-1Computer Science 425Distributed SystemsCS 425 / CSE 424 / ECE 428Fall 2010Computer Science 425Distributed SystemsCS 425 / CSE 424 / ECE 428Fall 2010Indranil Gupta (Indy)August 24-December 7, 2010Lecture 1-29 2010, I. Gupta, K. Nahrtstedt, S. Mitra, N. Vaidya, M. T. Harandi, J. HouWebsite: http://www.cs.uiuc.edu/class/fa10/cs425/Lecture 29-2Lecture 29-2Our First Aim in this Course was…(first lecture)….Our First Aim in this Course was…(first lecture)….To Define the Term Distributed System(First lecture slide)Lecture 29-3Lecture 29-3Can you name some examples of Distributed Systems?Can you name some examples of Distributed Systems?•Client-Server (NFS)•The Web•The Internet•An ad-hoc network•A sensor network•DNS•Gnutella or BitTorrent (peer to peer overlays)•A datacenter, e.g., The Planet, or Amazon EC2/S3•(The Solar System?)•(Society?)•(Food Chain?)(First lecture slide)Lecture 29-4Lecture 29-4What is a Distributed System?What is a Distributed System?(First lecture slide)Lecture 29-5Lecture 29-5FOLDOC definitionFOLDOC definitionA collection of (probably heterogeneous) automata whose distribution is transparent to the user so that the system appears as one local machine. This is in contrast to a network, where the user is aware that there are several machines, and their location, storage replication, load balancing and functionality is not transparent. Distributed systems usually use some kind of client-server organization.(First lecture slide)Lecture 29-6Lecture 29-6Textbook definitionsTextbook definitions•A distributed system is a collection of independent computers that appear to the users of the system as a single computer [Andrew Tanenbaum] •A distributed system is several computers doing something together. Thus, a distributed system has three primary characteristics: multiple computers, interconnections, and shared state[Michael Schroeder] (First lecture slide)Lecture 29-7Lecture 29-7A working definition for usA working definition for usA distributed system is a collection of entities, each of which is autonomous, programmable, asynchronous and failure-prone, and communicating through an unreliable communication medium.•Our interest in distributed systems involves –design and implementation, maintenance, study, algorithmics•Entity=a process on a device (PC, PDA)•Communication Medium=Wired or wireless network•What Evidence/Examples have we seen?(First lecture slide)Lecture 29-8Lecture 29-8Problems we have Seen and Solved Since ThenProblems we have Seen and Solved Since Then•Failure Detectors •Time and Synchronization•Global States and Snapshots•Multicast Communications •Mutual Exclusion •Leader Election •Impossibility of Consensus•Peer to peer systems – Gnutella and Chord•Cloud Computing •Networking and Routing•Sensor Networks•Measurements from real systemsLecture 29-9Lecture 29-9Problems we have Seen and Solved in this ClassProblems we have Seen and Solved in this Class•Failure Detectors •Time and Synchronization•Global States and Snapshots•Multicast Communications •Mutual Exclusion •Leader Election •Impossibility of Consensus•Peer to peer systems – Gnutella and Chord•Cloud Computing •Networking and Routing•Sensor Networks•Measurements from real systemsBasic Theoretical ConceptsBridge to SystemsWhat Lies BeneathLecture 29-10Lecture 29-10Problems we have Seen and Solved in this Class (2)Problems we have Seen and Solved in this Class (2)•RPCs & Distributed Objects •Concurrency Control•Replication Control•Gossiping•Self-stabilization•Distributed File Systems •Distributed Shared Memory •Byzantine Fault-tolerance•SecurityBasic Building BlocksDistributed Services(e.g., databases)Distributed Apps that people use directlyEasy programmingNecessary propertiesBasic Theoretical ConceptsLecture 29-11Lecture 29-11Problems we have Seen and Solved in this Class (3)Problems we have Seen and Solved in this Class (3)•Midterm•HW’s and MP’s–A new cloud computing application from scratch!How to get good grades(and regrades, and jobsin some cases)Something to boastabout to your friends(and in interviews!)Lecture 29-12Lecture 29-12A range of Challenges for DesignersA range of Challenges for Designers• •Heterogeneity•Openness•Security•Scalability•Failures•Concurrency•Transparency• • What are these?(First lecture slide)Lecture 29-13Lecture 29-13What we Have Learned Since ThenWhat we Have Learned Since Then•Heterogeneity – protocols should run in spite of heterogeneous nodes, e.g., supernodes in Kazaa, variety of nodes in a cloud•Openness – each service/protocol can build on other services/protocols, e.g., layered or stacked architecture•Security – it should be possible to add-in security to any existing protocol/system, e.g., encryption and signatures•Scalability – clouds and peer to peer systems need to scale in overhead as the size of the system increases•Failures – any protocol should be tolerant to the failure of nodes and of communication•Concurrency – the more this is, the better the performance, but is a tradeoff with consistency requirements•Transparency – clouds, distributed file systems, transactions, virtual synchrony, sequential consistency, etc. provide an abstraction of one property while allowing sufficient flexibility at run-timeLecture 29-14Lecture 29-14Problems we have Seen and Solved in this Class(and relation to other courses)Problems we have Seen and Solved in this Class(and relation to other courses)•Failure Detectors •Time and Synchronization•Global States and Snapshots•Multicast Communications
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