Runtime Environment

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Introduction
3-Tier Client/Server Overview by Gary
Rau DS513 April 29, 1999 http//people.ce.mediaon
e.net/grau/clientserver.html
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What is Client/Server?

• 1) Client/Server describes the relationship
  between two computer programs in which one
  program, the client, makes a service request from
  another program, the server, which fulfills the
  request.
• 2) Tiers describe the logical partitioning of an
  application across clients and servers.

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2-Tier and 3-Tier Architecture

• 2-Tier splits the processing load in two.
  Application logic runs on client, which
  communicates with data on server.
• 3-Tier splits the processing load between clients
  that run user interface logic, application server
  running business logic, and database/legacy
  application.

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Characteristics of Client/Server Systems

• Service
• Shared resources
• Asymmetrical protocols
• Transparency of location
• Platform independence
• Message-based exchanges
• Encapsulation of services
• Scalability
• Integrity

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2-Tier vs 3-Tier Comparison I
Comments
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3
Characteristic
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2-Tier vs 3-Tier Comparison II
Comments
2
3
Characteristic
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2-Tier vs 3-Tier Comparison III
Comments
2
3
Characteristic
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2-Tier vs 3-Tier Comparison IV
Comments
2
3
Characteristic
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Client/Server Technologies

• File Servers
• Database Servers
• Transaction Servers
• Groupware Servers
• Object Application Servers
• Web Application Servers

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Client/Server withFile Servers
Client
Communication Protocols
Server
Server
PageServer
Application
File Server
File Calls
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Client/Server with Database Servers
Client
Communication Protocols
Server
Server
PageServer
Application
DBMS Server
SQL Calls
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Client/Server withTransaction Servers
Client
Communication Protocols
Server
Server
PageServer
Application
DBMS TP Monitor
Transactions
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Client/Server with Groupware Servers
Client
Communication Protocols
Server
Server
PageServer
Application
Groupware Server
Groupware Messages
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Client/Server with Object Application Servers
Client
Communication Protocols
Server
ORB
ORB
Server
PageServer
Application
Object Services
Remote Method Invocation
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Client/Server with Web Application Servers
Client
Communication Protocols
Server
Server
PageServer
Application
CGI
Application
HTTP over TCP/IP
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Middleware I

• The / in Client/Server
• All the distributed software needed to support
  interactions between clients and servers
• Client-side API to invoke a service
• Transmission of request and response over network

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Middleware II

• Provide platform for running server-side
  components responsible for
• Load balancing
• Integrity of transactions
• High availablity
• Secure environment

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Client/Server Software Infrastructure
Client
Middleware
Server
Service-Specific
ODBC TxRPC Mail ORB HTTP
Browser
DSM
GUI/OOUI
SNMP CMIP Tivoli/ORB
NOS
Directory Security Distributed File
DSM
RPC Messaging Peer-to-Peer
DSM
CustomServer
Transport Stack
OS
OS
NetBIOS TCP/IP IPX/SPX SNA
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Component-Based Architecture

• Develop in small steps (4X4)
• Applications reuse components
• Encapsulate services
• Off-the-shelf, mix-and-match
• Component environments get better with age

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Component Types

• Services encapsulate a business function
• Objects encapsulate specific data with the
  associated business functions
• Stateless objects retrieve required instance data
  when needed, and update database when done
• Stateful objects are unique. Changes in state
  must be captured by the infrastructure.

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Design Patterns

• Greenfield
• Turbocharger
• Integrator

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Greenfield Pattern
Graphical User Interface
Services
Database
GUI/OOUI
TP Monitor or OTM
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Turbocharger Pattern
Existing System
Graphical User Interface
Services and Data
GUI/OOUI
TP Monitor or OTM
Middle-Tier Database
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Integrator Pattern
Existing System
Graphical User Interface
Services and Data
GUI/OOUI
TP Monitor or OTM
Middle-Tier Database
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When to use 3-Tier

• gt 50 services or classes
• gt 1 application language or development
  organization
• gt 1 different data source
• gt 3 years application life (especially if
  modifications/additions are expected)
• gt 50,000 transactions per day
• gt 300 users on same system using same database
• significant interapplication communication
• growth expectations

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Secrets for 3-Tier Success

• Keep it simple
• Design up front
• Buy, dont build
• Rely on industry standards
• Use a TP Monitor or OTM
• Take baby steps
• Use outside help
• Address system management during development
• Test, test, test
• Develop a rollout plan

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Overview of scripting lang.

• Scripting languages are used for adding client
  side interaction, publishing live and dynamic
  data to web site and an ability to communicate
  with components in application server is making
  them a very important in building multitier
  architecture for organizations.

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Where scripting lang is important

• 1) Datawarehousing. Plays a major role in
  publishing data out to web
• 2) Internet and Intranet Applications. eg Fed Ex.
• 3) Applications where deployment is major pain
  and has lot of remote users.

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Where they fit in mutitier architecture
Client
Middle Tier
Data
Web Server
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Runtime Environment
Client
Middle Tier
Data
Web Server
PageServer
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Runtime Environment
Client
Middle Tier
Data
Web Server
PageServer
TransactionServer
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Runtime Environment
Client
Middle Tier
Data
Web Server
PageServer
TransactionServer
Interface
CustomServer
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Runtime Environment
Client
Middle Tier
Data
Web Server
Browser
Very Thin
PageServer
TransactionServer
Interface
CustomServer
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Runtime Environment
Client
Middle Tier
Data
Web Server
Browser
Very Thin
PageServer
Browser
Thin
TransactionServer
Interface
CustomServer
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Scripting in Multitier Architecture
Client
Middle Tier
Data
Web Server
Browser
Very Thin
PageServer
Browser
Thin
TransactionServer
Interface
Stand-aloneApplication
CustomServer
Rich
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Thick or thin client ??
How user utilize system?
Heavy dataentry
VB Client
VB Client
Heavy Batchprocessing
Instant ReportAccess
ASP Client
ASP Client
Mainly External Access
System consideration based on heavy database
access and development team
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Major vendors supporting scripting language
deployment
Page Server
client
Sybase PowerDynamoActive Server pages Netscape
Livewire(javascript)Cold Fusion
browser
Database
JaguarCTS MTS SilverStream Oracle app
server NetDynamics
Thick client
Component Server
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Where CGI fits in

• CGI. The classic way to perform server-side
  functions is via Common Gateway Interface (CGI).
  Many CGI programs use Perl, a scripting language
  well-suited to the task. However, you can write
  CGI programs in practically any language
  including C, Python, and Java. Without careful
  planning, CGI can introduce security holes in
  your server, and CGI programs are usually hard to
  debug and difficult for casual programmers to
  write.

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Server side scripting(eg ASP)

• ASP is a deployment environment for server side
  scripting
• Client call the page server where the scripts
  resides.
• Scripts then query against the database or
  components to create dyanamic content on the
  client.

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Server side scripting(eg ASP)

• Jscript(competition of javascript) and Vbscript
  are the scripting languages used in ASP
  environment.
• ASP files on the server can be updated at any
  time. Simply save the changes to the file and the
  script will be automatically compiled the next
  time the Web page is loaded.

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Server side scripting(eg ASP)

• ASP includes five standard objects for global use
  
• Request -- To get information from the user
• Response -- To send information to the user
• Server -- To control the Internet Information
  Server
• Session -- To store information about and change
  settings for the user's current Web-server
  session
• Application -- To share application-level
  information and control settings for the lifetime
  of the application

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VBscript(Overview)

• Visual Basic Scripting Edition, also known as
  VBScript, enables authors to create scripts using
  a subset of the Microsoft Visual Basic language.
  If you are already a Visual Basic programmer, or
  if you are not a programmer but are looking for a
  scripting language that is easy to learn,
  VBScript might be the right language for you.
  VBScript is implemented as a fast, portable
  interpreter for use in Web browsers and
  applications that use ActiveX controls, Java
  applets, and OLE Automation servers.

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VBScript -- Features

• Error handling. VBScript has a subset of the
  error handling provided by Visual Basic. This
  includes the error object and on error resume
  next. Error handling is very important when
  developing server-side code, since most of the
  functionality will require access to external COM
  objects, which could throw errors.
• Formatting. VBScript has the ability to format
  dates, numbers, and currency built into the
  language.

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VBScript -- Features

• Easier COM integration. Many COM objects return
  information in the form of a collection. VBScript
  has built-in support for iterating through
  collections
• Standard Event-binding Syntax. Visual Basic
  developers will immediately recognize the
  object_event (sub button1_onclick) naming
  convention for event handlers. VBScript works in
  exactly the same way, so in any application that
  supports event binding (such as Internet
  Explorer, Outlook, and Windows Scripting Host),
  you can use this syntax for your event hook-up
  code.

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VBScript -- Advantages

• Easy to understand and master. VBScript's biggest
  asset is that it's Basic, a language designed to
  be learned quickly. Visual Basic has brought
  Basic users some of the advantages of more
  complex languages, while not losing sight of the
  fact that the language should be easy to
  understand.
• It's Visual Basic. All the skills learned with VB
  instantly apply to VBScript. Also, an enormous
  community exists to provide training, books, and
  magazines for learning Visual Basic.
• Flexible. VBScript can be used in a wide variety
  of applications, and Microsoft is committed to
  ensuring that wherever script is part of an
  application, VBScript will be included.

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VBScript --- Syntax

• ltCENTERgt
• ltPgt
• ltH2gtHello, world samplelt/H2gt
• ltINPUT TYPEBUTTON VALUE"Click me"
  NAME"BtnHello"gt
• lt/CENTERgt
• ltSCRIPT LANGUAGE"VBScript"gt
• lt!--
• Sub BtnHello_OnClick
• MsgBox "Hello, world!", 0, "My first active
  document"
• End Sub
• --gt
• lt/SCRIPTgt

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JScript(Overview)

• JScript is Microsoft's implementation of an
  ECMA-compliant scripting language (like
  JavaScript) that is targeted specifically to the
  Internet. Like VBScript, JScript is implemented
  as a fast, portable interpreter for use in Web
  browsers and applications that use ActiveX
  controls, Java applets, and OLE Automation
  servers. JScript is not Java and has nothing to
  do with Java. It is closer in syntax to C or C.

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Jscript Features

• Dynamic JScript was designed as a completely
  dynamic language that is, you can effectively
  redefine your program on the fly. While this has
  a number of potential disadvantages, it does give
  you the ultimate flexibility in your scripts.
  This is particularly useful in DHTML programming,
  since DHTML allows you to dynamically manipulate
  the object model. If you really want to drive
  DHTML, you might want to consider using JScript
  instead of VBScript.
• Object oriented JScript certainly isn't a
  traditional class-based, object-oriented
  language, but it does provide an effective
  alternative based on prototypes. This allows you
  to reap the benefits of object orientation
  without the statically defined nature of classes.
  

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Jscript - Features

• Regular expressions A main reason why Perl has
  such a huge following. Regular expressions add
  the ability to search for expressions in strings.
  This is exceptionally useful on the server and,
  increasingly, on the client.
• Eval Provides the ability to immediately
  evaluate code at runtime. This allows you to
  dynamically redefine logic dependent at run time.
  This is especially useful when used in
  conjunction with Remote Scripting, which works
  with VBScript as well.

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Jscript -- Advantages

• Broad reach. JScript is pretty much guaranteed to
  run in any browser, anywhere. If your page really
  must work in any browser, this is the language
  for you.
• All those books in the bookstore. How many books
  can there be? If you want to learn JScript, there
  are myriad books to help you.
• Similarity to C and Java. If you are a C or Java
  programmer, the JScript syntax is going to be
  familiar to you.

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JavaScript Overview

• Netscapes compact, object-based scripting
  language for developing client and server
  Internet applications.
• Not Java .. Or is it?

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Client-side JavaScript

• Embedded directly with HTML
• As with HTML, JavaScripts functions are built
  into the browser
• Example code

ltscript language"JavaScript"gt lt!--
document.write("Hello World!")
//--gt lt/scriptgt
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LiveConnect in JavaScript

• Allows Java and JavaScript code to communicate
  with each other
• From JavaScript, you can instansiate Java objects
  and access their public methods and fields
• From Java, you can access JavaScript objects,
  properties and methods

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LiveConnect in JavaScript

• Example Code

ltSCRIPTgt lt!-- if ((navigator.appVersion.indexOf("4
.") ! -1) (navigator.appName.indexOf("Netscape
") ! -1)) ip "" java.net.InetAddres
s.getLocalHost().getHostAddress()
document.write("Your IP address is "
ip) else document.write("IP Address
only shown in Netscape with Java
enabled!") //--gt lt/SCRIPTgt
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ServerSide JavaScript

• Serve more Client JavaScript and HTML
• Database Connectivity through LiveWire
• Corba Object Connectivity through LiveConnect

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Database Connectivity - LiveWire
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Corba Connectivity - LiveConnect
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(No Transcript)
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SilverStream Overview

• What is SilverStream
• The birth and success of SilverStream

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SilverStreams 3-tier Architecture
Database Server
Client
SilverStream HTTP Server
Database Server
Tier 1
Tier 2
Tier 3
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Benefits of SilverStreams 3-Tier Architecture

• Security management
• Code Management
• Data Valication

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SilverStream and Firewalls
External
P r o x y S e r v e r
F I r e w a l l
Database Server
SilverStream Client
SilverStream Server
SilverStream Client
Database Server
SilverStream Client
Internal
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SilverStream and Web Servers
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Client
Server
Session Info
Session
thread
Client Connection
initial connection
execute request
thread
thread
thread
Connection Pool
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server/database connections
Database Server
Client
Database Server
SilverStream Server
Client
Database Server
Client
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javax.servlet. ServletRequest
1
URL Request
service event
Explorer
javax.servlet. ServletResponse
2
3
Netscape
HTTP Listener (Servlet)
javax.servlet. ServletResponse
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SilverStream and Page Management

• Java Presentations
• Dynamic Page Presentations

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Oracle Database
Server
Sybase Database
request
Client
DSO
Lotus Notes
Result
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Business Objects and Corba Objects in SilverStream
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Other Features of SilverStream

• SilverStream and E-mail
• SilverStream and JAR(java archive) files
• SilverStream and JavaBeans

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SilverStream Security
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Load Balancing and Fail-over in SilverStream
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In the Distance with SilverStream
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Load Balancing
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Topics

• Concepts
• What is Load Balancing?
• Why do we need load balancing?
• What is essential for a load balancer?
• Architecture example Silverstream
• Common Algorithms
• Vendors

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Concepts What is Load Balancing?

• Evenly distribute network processing, database
  access, transactions.
• Example Clustering
• distribute incoming transactions evenly
• redirect requests

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Concepts Why do we need load balancing?

• Handling multiple requests, while ensuring
• optimal response time
• quality performance
• The cluster of servers have even workload and
  operate at maximum efficiency.

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Concepts What is essential for a load balancer?

• Retain the state of all servers it is managing.
• Have a good algorithm ? efficient load balancing
  plan

Example of a good load balancing
architecture(Silverstream) ...
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Silverstream Load Balancing Architecture
Application Server
Dispatcher
Web Server ISAPI or NSAPI Layer
Load Balancer
Application Server
HTTP
Cache Manager
Application Server
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Silverstream Load Balancing Architecture
Application Server
Dispatcher
Web Server ISAPI or NSAPI Layer
Load Balancer
Application Server
HTTP
Cache Manager
Application Server

• Dispatcher
• receives client requests
• consults load balancer
• receives routing plan
• forwards requests

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Silverstream Load Balancing Architecture
Application Server
Dispatcher
Web Server ISAPI or NSAPI Layer
Load Balancer
Application Server
HTTP
Cache Manager

• Load Balancer
• the process to maintain a state of all servers
  come up with a balancing plan

Application Server
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Silverstream Load Balancing Architecture
Application Server
Dispatcher
Web Server ISAPI or NSAPI Layer
Load Balancer
Application Server
HTTP
Cache Manager

• Cache Manager
• immediately update the cache
• send invalidation commands (parallel)
• able to assume all servers are in sync all the
  time Load Balancer
• the process to maintain a state of all servers
  come up with a balancing plan

Application Server
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Common Algorithms

• Sender Initiated Algorithms

• Receiver Initiated Algorithms (more effective)

• Symmetrically Initiated Algorithms
• Adaptive Algorithms

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Some Vendors

• Alteon networks Inc. ACEswitch
• ArrowPoint Communications Inc. Content Smart
  Switch
• Coyote Point Systems Inc. Equalizer