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    DCS Intro

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    Rohan Desai
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    DCS Intro

    Uploaded by

    Rohan Desai
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    DCS_Intro

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    DCS-Intro

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    4 views28 pages

    DCS Intro

    Uploaded by

    Rohan Desai
    DCS_Intro

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 28

    Distributed Computing Systems

    Distributed System

    A distributed system is:

    A collection of independent
    computers that appears to its
    users as a single coherent
    system.
    Why Distributed Systems?
    • Distributed (and mobile) users
    – Desire to access data/resources
    • Distributed data/information
    – World Wide Web
    • Distributed organizations
    – Multi-location & multinational corporations
    • Distributed resources
    – Distributed file systems, grids, web farms
    • Enabling technology:
    – Advances in communications and networks
    Characteristics of Distributed Systems
    • Hides heterogeneity and internal workings
    • Easy to expand or scale
    • Continuous availability
    • Layered design
    • Examples
    – Networked workstations
    – Distributed databases
    – WWW
    – Cloud and edge systems
    – Internet of Things, Sensor networks, etc.
    Distributed System Organization

    1.1

    A distributed system organized as middleware.


    Note that the middleware layer extends over multiple machines.
    Design Goals
    • Make resources available to users
    – Enable resource sharing in a controlled manner
    • Transparency
    – Hide distributed nature
    • Openness
    – Complies to standards with regard to syntax and
    semantics
    – Interoperability
    • Security & privacy
    • Scalability & performance
    Transparency in a Distributed System
    Transparency Description
    Hide differences in data representation and how a
    Access
    resource is accessed
    Location Hide where a resource is located
    Migration Hide that a resource may move to another location
    Hide that a resource may be moved to another
    Relocation
    location while in use
    Replication Hide that a resource may have multiple copies
    Hide that a resource may be shared by several
    Concurrency
    competitive users
    Failure Hide the failure and recovery of a resource
    Hide whether a (software) resource is in memory or
    Persistence
    on disk

    • How much transparency is needed?


    • How much can we achieve?
    Openness Security & Privacy
    • Openness – Follows rules that describe syntax and
    semantics
    – Interface definition language
    – Interoperability, portability
    – Mechanism-policy separation
    • Security
    – Access control
    – Data integrity
    – Data/service availability
    – Copyright protection
    Scalability
    • Scalability with respect to size
    • Scalability with respect to geographical location
    • Scalability with respect to management

    Concept Example

    Centralized services A single server for all users

    Centralized data A single on-line telephone book

    Centralized algorithms Doing routing based on complete information

    Scalability Problems
    Characteristics of Distributed Algorithms
    • Single machine does not have complete
    information
    • Decisions are made based on local information
    • Failure of a node does not cause the algorithm to
    fail
    • No global clock
    • Distributed algorithms are much harder than
    centralized algorithms
    Geographical Scalability Challenges
    • Synchronous communication
    – Waiting for a reply does not scale well!!
    • Unreliable networks
    – Broadcasting does not work
    • Centralized components
    – Will eventually become bottlenecks
    • Multiple administrative domains
    – Security mechanisms do not come for free
    Scalability Techniques
    • Hiding communication latencies
    – Asynchronous communication
    – Reduce amount of data transmitted
    • Distribution
    – Spreading work across system
    • Caching and replication
    – Make copies of data and services
    • Balance load
    – Avoid hot spots
    Scaling Techniques

    1.4

    The difference between letting:


    a) a server or
    b) a client check forms as they are being filled
    Scaling Techniques (2)

    1.5

    An example of dividing the DNS name space into zones.


    Types of Distributed Systems
    • High-Performance Computing Systems
    • Cluster computing
    • Grid computing
    • Distributed Information Systems
    • Transaction processing systems
    • Enterprise application integration
    • P2P systems
    • Distributed Pervasive Systems
    • Mobile networks
    • Sensor networks
    Cluster Computing
    • Super computing using PCs/workstations
    • Used for parallel programming
    • Homogeneity among nodes
    • Master allocates nodes to tasks
    • Compute nodes run standard operating systems
    (and may be a very thin middleware)
    • Middleware consists of parallel programming
    libraries
    Cluster Computing Systems

    An example of a cluster computing system.


    Grid Computing
    • Formed from heterogeneous set of machines
    • May belong to different organizations
    • Virtual organization
    • Resource access and management
    • 4-layered organization
    • Fabric layer – Interfacing to local resources
    • Connectivity layer – Connection handling and security
    • Resource layer – Managing a single resource
    • Collective layer – Simultaneous management of multiple
    resources
    • Application layer – Hosts applications
    Grid Computing Systems

    A layered architecture for grid computing systems.


    Distributed Information Systems
    • Lots of networked applications
    • Sometimes belonging to different organizations
    • Little interoperability
    • Simplest integration
    • Bundling operations together at client end
    • Enterprise application integration
    • Applications talking to each other
    Transaction Processing Systems
    Properties of Transactions

    • Atomic: To the outside world, the transaction


    happens indivisibly.
    • Consistent: The transaction does not violate system
    invariants.
    • Isolated: Concurrent transactions do not interfere
    with each other.
    • Durable: Once a transaction commits, the changes
    are permanent.
    Examples

    • Banking example

    • Airline ticket booking example


    Nested Transactions

    • Transactions constructed from multiple sub-


    transactions
    • Example: Travel Agent
    • Problem with nested transactions
    • What if one of the sub-transactions fail?
    • TP monitor architecture
    Nested Transactions
    Transaction Processing Architecture

    The role of a TP monitor in distributed systems.


    Enterprise Application Integration

    Middleware as a communication facilitator in


    enterprise application integration.
    Distributed Pervasive Systems
    • Ad hoc composition
    • Extreme heterogeneity
    • Wired network/wireless network
    • High churn rate
    • Resource constraints
    • Contextual changes
    • Possible mobility

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