eCommerce Technology 20-751 Lecture 4: Web Architecture

20-751 ECOMMERCE TECHNOLOGY

FALL 2003

COPYRIGHT © 2003 MICHAEL I. SHAMOS

eCommerce Technology20-751

Lecture 4: Web Architecture


FALL 2003


Client-Server Model

INTERNET

CLIENT(Often a Web browser)

SERVER

Client makes requestsServer responds


FALL 2003


Two-Tier Architecture

SOURCE: FOURNIER

TIER 1:CLIENT

TIER 2:SERVER Server performs

all processing

Web ServerApplication ServerDatabase Server

This architecture is obsolete. Server does too much work.


FALL 2003


Three-Tier Architecture

TIER 1:CLIENT

TIER 2:SERVER

TIER 3:BACKEND

Application serveroffloads processing

to tier 3

SOURCE: FOURNIER

Web Server +Application Server

Note: Using 2 computers instead of 1 can result in a huge increase insimultaneous clients. Depends on % of CPU time spent on database access.


FALL 2003


N-Tier Architecture

SOURCE: FOURNIER

Achieves full separation of function and administrationHuge number of simultaneous clients

Managed andtuned by DBA

Optimized forweb pagedelivery

Coded forspecific

application


FALL 2003


InterShop Architecture

SOURCE: INTERSHOP


FALL 2003


Connecting to Legacy Systemsby “Wrapping”

WebApp

Web ServerWeb Server

LegacyApp

MAINFRAMEMAINFRAME

“WRAPPER”

WrapperMiddleware


FALL 2003


Connecting to Legacy Systems

The “screen scraper”

Client Web server Legacy database

Terminalscreen data

Screen scraper

Existing application

HTML data

HTMLdata

Legacy system(mainframe)

SOURCE: WIM GEVERS


FALL 2003


Screen Scraping

• Some systems produce as their only output commands to 80 x 24 display terminals

• Sequences of characters telling the terminal to move its cursor and display data, e.g. ^M0238Jan. ^M024416, ^M02482000displays “Jan. 16, 2000” in row 2, starting at col. 38

• Screen scraping involves virtual simulation of the display terminal to retrieve the data

• Vendors

– Intelligent Environments

http://www.screensurfer.com/


FALL 2003


Document Repository

Office

Tool

Internet & Web

Web

Browser

DataWarehouse

Query

Tool

EnterpriseSystem

ERP

Client

ClientInformation

System

CRM

Client

Groupware Database

Groupware

Client

E N T E R P R I S E P O R T A L

Content DirectoryText Metadata

Embedded Services Web ToolsApplications

Portal ArchitecturePartnersEmployees Customers

SOURCE: PLUMTREE

Resources

User Interface

Feedback Customer Satisfaction

En

terp

rise

Po

rtal

Ser

vice

sR

eso

urc

es

S

ecu

rity

M

etri

cs

Integration

Navigation Methods

BrowseSearch

Communication Process

Publishing Distribution

BusinessRules

Personalization Customization

Information Architecturemetadata - organization services

KnowledgeBaseArchive

Document Stores

Public FoldersPersonnel HR Data Collaboration Search Index

LOBPortals

Portal Architecture

SOURCE: MIKE CRANDALL, GATES FOUNDATION

LOB = “LINE OF BUSINESS”


FALL 2003


Server Farms

Web Servers

App Servers

DB Servers

Router

Intranet Firewall

Network Switch

Router

Internet Firewall

Network Switch

SOURCE: ATESTO

• To serve many clients, one server is not enough• How do multiple servers cooperate?


FALL 2003


Communication

RequestRouting

Server Cluster (Server Farm)

Internet

Clients

Server farm

HTTP request

System Management

Router

SOURCE: CHU-SING YANG


FALL 2003


Server Selection Problem

Which network site?

Which server?

“Contact the weather service.”

Server Farm A Server Farm B

• Avoid scalabilityproblems of central servers bydistributing load

SOURCE: JEFF CHASE

Load Balancing Switch

‧‧

‧‧

‧‧‧

‧‧‧

Internet

Web Switch

Router

Server Farm

subnethttp://pds.cse.nsysu.edu.tw/job/

SVR.1

SVR.2

SVR.n

client

Internet

subnet

Virtual IP address

SOURCE: CHU-SING YANG


FALL 2003


Domain Names

• IP addresses are inconvenient to remember 128.2.218.2 v. euro.ecom.cmu.edu (fully qualified)

• Domain names are alphanumeric aliases for IP addresses. They form a tree structure of FQDNs:

ROOT

.GOV .COM .MIL .NET .EDU .ORG .IT

CMU PITT MITAMAZON MCKINSEY YAHOO

GSIA CS ECOM HEINZ

WWW YEN EURO DOLLAR PESO

207.237.113.94

128.2.218.2

208.216.182.15

128.2.218.4128.2.16.175


FALL 2003


Domain Name System

What is the IP addressof abc.foo.com?

SOURCE: CISCO SYSTEMS

client

Local DNSResolver

Try .com

Root DNS

.com DNS

Try foo.comfoo.com DNS

abc.foo.com is 202.168.14.12

+ Cache

202.168.14.12

• Large, distributed, worldwide database• Maps domain names to IP addresses

URL-Based Load BalancingSubstring matching for:

• “images”• “.gif”• “.jpg”

GET/www.foo.com/event/reg.bin

GET /www.foo.com/images/abc.gif

GET /www.foo.com/product/abc.html

Load distributed within group via any standard metric or URL hashing

Substring matching for:• “.cgi”• “.bin”• “.exe”

Substring matching for:

• “.html”

• Servers optimized for specific content-types

• Substring match on URL directs HTTP requests to designated server farm

– Load balancing using configured algorithm or,

– URL Hashing forwards requests for each unique URL to same server to take advantage of server memory caching

SOURCE: SUN


FALL 2003


DNS Round Robin Balancing

“lookupwww.nhc.noaa.gov”

a

DNS server fornhc.noaa.gov

b c d

client networkDNS server

“www.nhc.noaa.gov isIP address a”

(or {b,c,d})Idea: When an IPaddress is requestedfor nhc.noaa.gov,return a differentIP address each time

SOURCE: JEFF CHASE

SERVER

CLIENT

Web Data Center

SOURCE: SUN


FALL 2003


Global WAN Architecture

BIG-IP

Server Array

Webmaster

Site Inewyork.domain.com

Site IIItokyo.domain.com

Site IIlosangeles.domain.com

Userlondon.domain.com

Local DNS

DNS

GLOBAL-SITE

Router

BIG-IP

Internet

SOURCE: EDWARD CHOW


FALL 2003


Client- and Server Side Programming

Client

Internet

Server

HTML

Dynamic HTML

Applets

ActiveX Controls

JavaScript

CGI/Perl, C

XML

ASP

Servlet

JSP

SOURCE: IIT


FALL 2003


Tiers and URLs

WebServer DB

DB

Web app

Web app

Web app

Web app

http: // 10.0.0.1 / catalog / display.asp ? pg = 1 & product = 7

SOURCE: NTOBJECTIVES.COM

URLs can be used for application routing


FALL 2003


PHP Process Flow

Web

Server

PHP

Pre-

processor

.php

source

fileBrowserInternet

Request for .php file

Raw .php source

HTML is substituted for PHP code

HTML

SOURCE: M. HAMILLPHP originally mean “Personal Home Page”


FALL 2003


Website Components

WebServer DB

DB

Web app

WebClient Web app

Web app

Web app

HTTPrequest

(cleartext or SSL)

HTTP reply(HTML,

Javascript, VBscript,

etc)

Plugins:•Perl•C/C++•JSP, etc

Database connection:•ADO,•ODBC, etc.

SQL Database

•Apache•IIS•Netscape etc…

Firewall

SOURCE: NTOBJECTIVES.COM


FALL 2003


Major Ideas

• Client-server model• Three-tiered (n-tiered) architecture• Legacy connections• Portals• Server Farms• Web development tools• Client- and server-side tools


FALL 2003


QA&

eCommerce Technology 20-751 Lecture 4: Web Architecture

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