Web Architecture

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Web Architecture

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Client-Server Model
CLIENT (Often a Web browser)
SERVER
INTERNET
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Two-Tier Architecture
This architecture is obsolete. Server does too
much work.
SOURCE FOURNIER
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Three-Tier Architecture
TIER 3 BACKEND
TIER 2 SERVER
TIER 1 CLIENT
Application server offloads processing to tier 3
Web Server Application Server
Note Using 2 computers instead of 1 can result
in a huge increase in simultaneous clients.
Depends on of CPU time spent on database access.
SOURCE FOURNIER
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N-Tier Architecture
Optimized for web page delivery
Coded for specific application
Managed and tuned by DBA
Achieves full separation of function and
administration Huge number of simultaneous clients
SOURCE FOURNIER
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InterShop Architecture
SOURCE INTERSHOP
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Connecting to Legacy Systemsby Wrapping
WRAPPER
Web Server
MAINFRAME
Web App
Legacy App
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Connecting to Legacy Systems
The screen scraper
Legacy system(mainframe)
Terminalscreen data
HTML data
HTMLdata
Screen scraper
Existing application
Legacy database
Web server
Client
SOURCE WIM GEVERS
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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

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Portal Architecture
E N T E R P R I S E P O R T A L
SOURCE PLUMTREE
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Portal Architecture
LOB LINE OF BUSINESS
SOURCE MIKE CRANDALL, GATES FOUNDATION
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Server Farms

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

Network Switch
Network Switch
Internet Firewall
Intranet Firewall
DB Servers
App Servers
SOURCE ATESTO
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Server Cluster (Server Farm)
Clients
HTTP request
Router
Request Routing
Communication
Server farm
System Management
SOURCE CHU-SING YANG
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Server Selection Problem
Server Farm A
Server Farm B
Which server?

• Avoid scalabilityproblems of central servers
  bydistributing load

Which network site?
Contact the weather service.
SOURCE JEFF CHASE
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Load Balancing Switch
client
http//pds.cse.nsysu.edu.tw/job/
Server Farm
Router
SVR.1
SVR.2
Web Switch
Virtual IP address
SVR.n
SOURCE CHU-SING YANG
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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 MIT
AMAZON MCKINSEY YAHOO
208.216.182.15
207.237.113.94
GSIA CS ECOM HEINZ
WWW YEN EURO DOLLAR PESO
128.2.218.4
128.2.218.2
128.2.16.175
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Domain Name System

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

What is the IP address of abc.foo.com?
Root DNS
202.168.14.12
.com DNS
Try .com
Try foo.com
foo.com DNS
Local DNS Resolver
abc.foo.com is 202.168.14.12
Cache
SOURCE CISCO SYSTEMS
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URL-Based Load Balancing

• 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
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DNS Round Robin Balancing
SERVER
a
b
c
d
DNS server for nhc.noaa.gov
www.nhc.noaa.gov is IP address a (or b,c,d)
Idea When an IP address is requested for
nhc.noaa.gov, return a different IP address each
time
CLIENT
lookup www.nhc.noaa.gov
client network DNS server
SOURCE JEFF CHASE
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Web Data Center
SOURCE SUN
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Global WAN Architecture
Site II losangeles.domain.com
Internet
Site I newyork.domain.com
Router
DNS
BIG-IP
BIG-IP
Local DNS
GLOBAL-SITE
Webmaster
Site III tokyo.domain.com
Server Array
User london.domain.com
SOURCE EDWARD CHOW
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Client- and Server Side Programming
Server
Client
HTML
CGI/Perl, C
Applets
ASP
ActiveX Controls
Servlet
Dynamic HTML
JSP
JavaScript
XML
SOURCE IIT
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Tiers and URLs
URLs can be used for application routing
http // 10.0.0.1 / catalog / display.asp ?
pg 1 product 7
Web Server
DB
Web app
Web app
DB
Web app
Web app
SOURCE NTOBJECTIVES.COM
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PHP Process Flow
Raw .php source
HTML is substituted for PHP code
PHP Pre- processor
Web Server
Browser
HTML
.php source file
Internet
Request for .php file
PHP originally mean Personal Home Page
SOURCE M. HAMILL
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Website Components
SQL Database
HTTP request (cleartext or SSL)
Firewall
Web Server
DB
Web Client
Web app
Web app
DB
Web app
Web app
HTTP reply (HTML, Javascript, VBscript, etc)

• Plugins
• Perl
• C/C
• JSP, etc

• Database connection
• ADO,
• ODBC, etc.

• Apache
• IIS
• Netscape
• etc

SOURCE NTOBJECTIVES.COM
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Major Ideas

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