chapter 1n2 characterization and design goals

8/3/2019 Chapter 1n2 Characterization and Design Goals

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Topic 1:

Introduction to Distributed Systems,Characterization and Design Goals

Dr Ahmad Suki Che Mohamed Arif

School of ComputingUUM CAS, Universiti Utara Malaysia


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1. What is a Distributed System

2. Examples of Distributed

Systems3. Common Characteristics

4. Basic Design Issues

5. Design Requirements6. Summary


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Fully

Distributed

D

ata

Processors

Control

Fully replicated

Not fully replicated

master directory

Local data,

local directory

Master-slave

Autonomous trans-

action based

Autonomousfully cooperative

Homog.special

purpose

Heterog.

special

purpose

Homog.general

purpose

Heterog.

general

purpose


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A programming languageis/was only compatible withcertain operating systems.

VB is only for MS Windows.

http://en.wikipedia.org/wiki/List_of_operating_systems
http://en.wikipedia.org/wiki/List_of_operating_systemshttp://en.wikipedia.org/wiki/List_of_operating_systems


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http://en.wikipedia.org/wiki/List_of_operating_systemshttp://en.wikipedia.org/wiki/List_of_operating_systems


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A client that is set to server A, will only usethat server resources.Event though many other computers are idle.


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A client that is set to server A, has to bereplaced if the server is not scalabled.Certain application can only be implemented in

certain types of machines.


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Certain database application/server mightnot able to be implemented if cantsupport a huge data.

It definitely needs to be distributed


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Mobile devices and computer/databaseservers are not connected.Computer applications are not accessible from

a mobile device.


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Computing in computer networksplatform?

Computing components are not in a single

computer (distributed across multiplecomputers on the network).

Resource sharing cloud computing.


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Definition: A distributed system is one in whichcomponents located at networked computerscommunicate and coordinate their actions only bypassing messages. This definition leads to the

following characteristics of distributed systems:concurrency of components

lack of a global clock

independent failures of components


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One component with non-autonomousparts

Component shared by users all the time

All resources accessible

Software runs in a single process

Single point of control

Single point of failure


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Multiple autonomous components

Components are not shared by allusers

Resources may not be accessible

Software runs in concurrent processeson different processors

Multiple points of control

Multiple points of failure

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Instructors Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5

Pearson Education 2012

Finance and commerce eCommerce e.g. Amazon and eBay, PayPal,online banking and trading

The information society Web information and search engines, ebooks,Wikipedia; social networking: Facebook and MySpace.

Creative industries and entertainmentonline gaming, music and film in the home, user-generated content, e.g. YouTube, Flickr

Healthcare health informatics, on online patient records,

monitoring patients

Education e-learning, virtual learning environments; distancelearning

Transport and logistics GPS in route finding systems, map services:Google Maps, Google Earth

Science The Grid as an enabling technology forcollaboration between scientists

Environmental management sensor technology to monitor earthquakes, floodsor tsunamis


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The emergence of pervasive networkingtechnologyDevices can be connected at any time and in

any place.

The emergence of ubiquitous computingcoupled with the desire to support usermobility in distributed systems.

The increasing demand for multimediaservices Including various real-time and on-demand


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intranet

ISP

desktop computer:

backbone

satellite link

server:

network link:


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8




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What are we trying to achieve when weconstruct a distributed system?

Challenges in distributed systemsHeterogeneity: variety and differences in computing

components Openness: uniform communication mechanism and

published interfaces for access to shared resources. Security Scalability

Failure Handling ConcurrencyTransparency


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Variety and differences in Networks Computer hardware Operating systems Programming languages

Implementations by different developers Middleware as software layers to provide a

programming abstraction as well as maskingthe heterogeneity of the underlying networks,hardware, OS, and programming languages(e.g., CORBA).

Mobile Code to refer to code that can be sentfrom one computer to another and run at thedestination (e.g., Java applets and Java virtual


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Openness is concerned with extensionsand improvements of distributed systems.

Detailed interfaces of components need to

be published.New components have to be integrated

with existing components.

Differences in data representation ofinterface types on different processors (ofdifferent vendors) have to be resolved.


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In terms of CONFIDENTIALITY, INTEGRITY &AVAILABILITY.

In a distributed system, all open resources need tobe allowed, while confidential data has to be

restricted to authorized users only. Security is required for Concealing the contents of messages: security and

privacy Identifying a remote user or other agent correctly:

authentication New challenges:

Denial of service attack Security of mobile code


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Adaptation of distributed systems toaccommodate more users

respond faster (this is the hard one)

Challenges:Controlling the cost of physical resources.

Controlling the performance loss

Preventing software resources running outAvoiding performance bottlenecks


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Hardware, software and networks mightfail independently.Example: DNS fail & web server limitation

cases

Solution & Challenge Issues:Detecting failures

Masking failures retransmitted when failure

occursTolerating failures informs user about the

problem


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Components in distributed systems areexecuted in concurrent processes.

Components access and update shared

resources (e.g. variables, databases,device drivers).

Integrity of the system may be violated ifconcurrent updates are not coordinated.Lost updates

Inconsistent analysis


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Distributed systems should be perceivedby users and application programmers as awhole rather than as a collection ofcooperating components.

Transparency has different aspects.

These represent various properties that

distributed systems should have.


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Access transparency: enables local and remote resources to be accessed using identical

operations.Location transparency: enables resources to be accessed without knowledge of their physical

or network location (for example, which building or IP address).

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.


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Enables local and remote informationobjects to be accessed using identicaloperations.

Example: File system operations inNFS.

Example: Navigation in the Web.

Example: SQL Queries


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Enables information objects to beaccessed without knowledge of theirlocation.

Example: File system operations in NFS

Example: Pages in the Web

Example: Tables in distributeddatabases


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Enables several processes to operateconcurrently using shared informationobjects without interference betweenthem.

Example: NFS

Example: Automatic teller machinenetwork

Example: Database management system


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Enables multiple instances of informationobjects to be used to increase reliabilityand performance without knowledge of thereplicas by users or application programs

Example: Distributed DBMS

Example: Mirroring Web Pages.


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Enables the concealment of faultsAllows users and applications to complete

their tasks despite the failure of other

components.Example: Database Management System


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Allows the movement of informationobjects within a system without affectingthe operations of users or applicationprograms

Example: NFS

Example: Web Pages


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Allows the system to be reconfigured toimprove performance as loads vary.

Example: Distributed make.


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Allows the system and applications toexpand in scale without change to thesystem structure or the applicationalgorithms.

Example: World-Wide-Web

Example: Distributed Database


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Case of the World Wide Web (refer tosection 1.6 pg 42 of the text book)

Networking and internetworking (Chapter

3).


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What are the entities that arecommunicating in the distributed systems?

How do they communicate, or, more

specifically what communication paradigmis used?

What (potentially changing) roles andresponsibilities do they have in the overall

architecture?How are they mapped on to the physical

distributed infrastructure (what is their


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Client-serverPeer-to-peer

Services provided by multiple servers

Proxy servers and cachesMobile code and mobile agents

Network computers

Thin clients and mobile devices


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Instructor s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5


Server

Client

Client

invocation

result

Serverinvocation

result

Process:Key:

Computer:


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Server

Server

Server

Service

Client

Client

A service provided by multiple servers


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Client

Proxy

Web

server

Web

server

serverClient


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a) client request results in the downloading of applet code

Web

server

ClientWeb

server

Applet

Applet code

Client

b) client interacts with the applet


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ThinClient

ApplicationProcess

Network computer or PCCompute server

network

a computeror a computer programwhich depends heavily on some

other computer (itsserver) to fulfill its traditional computationalroles.

The most common type of modern thin client is a low-end

computer terminalwhich concentrates solely on providing a

graphical user interfaceto the end-user.
http://en.wikipedia.org/wiki/Computerhttp://en.wikipedia.org/wiki/Computerhttp://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Computer_terminalhttp://en.wikipedia.org/wiki/Computer_terminalhttp://en.wikipedia.org/wiki/Graphical_user_interfacehttp://en.wikipedia.org/wiki/Graphical_user_interfacehttp://en.wikipedia.org/wiki/Graphical_user_interfacehttp://en.wikipedia.org/wiki/Computer_terminalhttp://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Computer


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Applications, services

Computer and network hardware

Platform

Operating system

Middleware

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Definitions of distributed systems andcomparisons to centralized systems.

The characteristics of distributed

systems.The eight forms of transparency.

The basic design issues.

Typical design requirements.Read Chapter 1 and Chapter 2 of the

textbook.

chapter 1n2 characterization and design goals

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