Advanced Internet and Web Systems
C. Edward Chow
Outline of the Talk
Syllabus
Introduction to WWW Systems
Survey of Web Cluster Systems
Survey of Caching Techniques
Server Selection and Load Balancing
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Introduction to WWW
Systems
Web Server
Hosting web pages
Retrieving
web pages
using HTTP
protocol
Internet
Web Client
Browser
Web Authoring System
create web pages
Publish
web pages
Scanner
Video capture
Web page: document written in HTML
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Sound card
3
What is Unique in WWW?
Hyperlink: Use Hypertext Markup Language HTML
to describe the document in ASCII text (extended to
iso-8859-1)
Naming scheme: Name object in the web with
Universal Resource Locator (URL) with syntax:
protocol://domain_name/<uri or path name>
HTTP: HyperText Transfer Protocol
a simple request-response protocol for transferring
HTML documents
ASCII text based (not binary, therefore easy to debug)
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Web Authoring System
Text Editor: type in HTML <tag> and content
HTML Editor: like normal word processor, user did
not have know a lot about HTML syntax, e.g.,
Netscape Page Composer, MS Front Page
Front Page takes another step by providing
templates and hyperlink management functions
Dreamweaver allows site management
(upload/download); editor understands PHP, XSLT,
XML, CSS, JavaScript syntax.
Most desktop publishing software and word
processor have built-in converters to convert from
their internal format to HTML format. For example
FrameMaker, Office2007
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Web Delivery Systems
Delivery web documents efficiently and
reliably to the web clients.
Content Distribution and Content Delivery
Performance is decided by
Web server performance
Network path performance
Client browser performance.
Use multiple physical servers (server farm),
and multiple server farms in wide area.
New generation of proxy servers/content
switches emerge.
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Content Delivery Network
(CDN)
Slow Response
Huge Requests
@Home
Clients
Host Server
PSINet
Sprint
QWest
UUnet
Mind
Spring
Server Crash
Gloobix
Clients
Clients
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Content Delivery Problems
http://www.akamai.com
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Use Client Cache/
Client Side Cache Server
Fewer Requests
Clients
Fast Response
Client
Cache
Clients
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PSINet
@Home
Sprint
Host
Server
UUnet
QWest
Mind
Spring
Client
Side
Cache
Server
Gloobix
Clients
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Use Mirror Sites
Need improvement by guiding the selection of mirror servers
with server load/network bandwidth measurement
Mirror Site Fewer Requests
Clients
PSINet
@Home
Host Server
Sprint
QWest
UUnet
Server
Clients
Mind
Spring
Fast Response
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Gloobix
Mirror Site
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Clients
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Edge Network Cache
Servers
Mirror Site
Fast Response
Clients
Cache
Server
PSINet
Client
Cache
Cache
Server
@Home
Cache
Server
Host Server
Sprint
Cache
Server
UUnet
QWest
Server
Mind
Spring
Clients
Fewer Requests
Client
Side
Cache
Server
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Gloobix
Edge
Network
Cache
Server
Mirror Site
Clients
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Architecture solutions for
scalable Web-server systems
(Fig. 1)
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Fig. 2. Model architecture for
a locally distributed Web
system
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Fig. 3. Architecture of a
cluster-based Web system
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Fig. 4. Architecture of a virtual
Web cluster
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Fig. 5. Architecture of a
distributed Web system
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Content Distribution
Secure, automate content/application distribution to
single (multiple server)/wide area Internet sites.
Provide replication, synchronization, staged rollout
and roll back.
With revision control, transmit only updates.
User-defined file distribution profiles/rules
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Content Delivery Problem
Cache Location Problem:
Where to put cache servers?
How many are needed?
When/where/how to push/delivery the
content?
How about dynamic content?
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Akamai Edge Delivery Service
Date
11/2000
# of Edge Servers
6000
# of Networks # of Countries
335
54
1/2009
15000
1000
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Peering Bottleneck Problem:
Access traffic evenly spread over 7400+ networks
(no one over 5%; most << 1%)
 Need to put edge servers in many networks.
Akamai delivers between 10-20% Internet traffic,
10B interactions/day.
1 hop to 85% of the world’s Internet users.
http://www.akamai.com/html/technology/nocc.html
http://www.akamai.com/html/technology/medium_res.asx
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F5 Web System Product
Site II
losangeles.domain.com
Internet
Internet
Site I
newyork.domain.com
Router
3-DNS
BIG-IP
BIG-IP
Local DNS
GLOBAL-SITE
Webmaster
Site III
tokyo.domain.com
Server Array
User
london.domain.com
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BIG/ip - Delivers High Availability
E-commerce - ensures sites are not only up-and-running, but
taking orders
Fault-tolerance - eliminates single points of failure
Content Availability - verifies servers are responding with the
correct content
Directory & Authentication - load balance multiple directory
and/or authentication services (LDAP, Radius, and NDS)
Portals/Search Engines – Using EAV administrators perform
key-word searches
Legacy Systems - Load balance services to multiple
interactive services
Gateways – Load balance gateways (SAA, SNA, etc.)
E-mail (POP, IMAP, SendMail) - Balances traffic across a
large number of mail servers
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3DNS Intelligent Load Balancing
Intelligent Load Balancing
QoS Load Balancing
Quality of Service load balancing is the ability
to select apply different load balancing
methods for different users or request types
Modes of Load Balancing
Round Robin
Least Connections
User-defined Quality-of-Service
Completion Rate (Packet Loss)
Global Availability
Topology Distribution
LDNS Round Robin
E-Commerce
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Ratio
Random
Round Trip Time
BIG/ip Packet Rate
HOPS
Access Control
Dynamic Ratio
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GLOBAL-SITE Replicate
Multiple Servers and Sites
File archiving engine and scheduler for automated site and
server replication
BIG-IP controls server availability during replication and
synchronization
Gracefully shutdown for update
update in group/scheduled manner
FTP provides transferring files from GLOBAL-SITE to target
servers (agent free, scalable)
RCE for source control
No client side software
Complete, turnkey system (appliance)
(adapt from F5 presentation)
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Intel NetStructure
Routing based on XML tag (e.g., given preferred treatment for
buyers, large volume)
http://www.intel.com/network/solutions/xml.htm
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1. Compared to SUN E450 server
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Simple Web Access Example:
Step1
Someone requests a document using a browser (Web Client)
on a computer connected to Internet
On a browser window Type in a URL,
http://news.netcraft.com/archives/web_server_survey.html
Equivalent of %telnet www.netcraft.co.uk 80 > out
GET /survey/ HTTP/1.0<cr>
<cr>
Here <cr> is “carriage return” entered by pressing
“enter”key
The browser parses the URL,
obtains domain name of url, www.netcraft.co.uk
asks Domain Name Server (DNS) for translating the
domain name to the IP address
with IP address the client computer set up a HTTP
connection to the server
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Computer Network
Local Area Network (LAN): a private-owned network within a single
building or campus of up to a few kilometer in size
(Tanenbaum).
Wide Area Network (WAN): a network that spans a large
geographical area, often a country or continent, and connects
LANs or MANs. It consists of transmission line (called circuits,
channels, or trunks) and switching elements (called switching
nodes, data switching exchanges or router).
web
host client
host
DNS
router
router
LAN
LAN
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DNS
web
server host
LAN
host
communication subnet
LAN
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Protocol and Protocol Layer
A set of rules for achieving a global objective
exercised by geographically distributed
nodes. (Robert Gallager, Prof. EE MIT)

Processing 



Communication 


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
Presentation 
End-to-End

Session
Application

Transport
Network
Data Link
Physical


Networking

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user-oriented functions
syntactic, format compatibility
value-added features to
transport connection
reliable transfer between
processes at different hosts
establish connection between
different hosts in a net
reliable transfer across a link
between neighboring hosts
attachment to network or
comm. line
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Protocol Data Encapsulation
Message between entities consist of two parts: header and payload.
Data from upper layer are put in the payload.
Header contains info to allow receiving
Data
end to deliver to the right upper layer entity.
TH: Transport Layer Header
AH Data
Application
Application
PH
Presentation
Session
SH
Transport
TH
Network
Data Link
NH
LH
Data
Presentation
Data
Session
Data
Transport
Data
Network
Data
LT
Physical
Data Link
Physical
Physical Transmission Medium
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Internet Protocol Layer
Interface
email
FTP
SMTP
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25
W3
Server
DNS
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2001
80
TCP
MINS
Server
Web
Client1
2002
UDP
Application
Layer
(4) SAP’s
Ports
Transport
Layer
(3)SAP’s
IP
Network
Layer
IP
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SAP: Service Access Point
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Simple Web Access Example:
Step2
Browser sends the following character string to server
GET /survey/ HTTP/1.0
User-agent: Mosaic for X windows/2.4
Accept: text/plain
Accept: text/html
Accept: image/*
httpd server
parses the request according to HTTP protocol 1.0
interprets rest of the metainfo for browser capabilities
Maps the /survey/ to c:/InetPub/wwwroot/survey/default.htm
a file path in its file system according to server configuration.
retrieves c:/InetPub/wwwroot/survey/default.htm or index.html
sends information back using HTTP/1.0 format
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Simple Web Access Example:
Step3
Server replies information using HTTP/1.0 format
HTTP/1.0 200 Document follows
Date: Tue, 19 Jan 1999 18:10:20 GMT
Server: NCSA/1.5
Content-type: text/html
<html>
<head><title>Netcraft Web Server Survey</title></head>
Server close file, set certain timeout and wait for next subsequent
requests, such as images/midi files referenced in the web page.
(called keep-alive connection). When time expires, disconnect the
connection.
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Simple Web Access Example:
Step3a
Browser send GET /sample.htm HTTP/1.0
Server replies
HTTP/1.0 404 Object Not Found
Content-Type: text/html
<body><h1>HTTP/1.0 404 Object Not Found
</h1></body>
Server close file, network connection, wait
for next request
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Simple Web Access
Example: Step4
Browser receives http response, a web document
with HTML tags, from the server.
Browser parses/processes the HTML document,
display the document content according the tags.
When other images/audio/video data are referenced
by <img> <object> <applet> tags, the browser
initiates the retrieval of those data.
Some of them will http requests to the same web
servers. That is the reason why keep-alive
connection improves the web server throughput.
A URL request may trigger many http requests to
several web servers.
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HTTP
HTTP1.0/1.1
http://www.w3.org/Protocols/rfc2068/rfc2068
A HTTP request consists of
method: GET, HEAD, POST, PUT, DELETE,
Universal Resource Identifier (URI)
Protocol version
other info to modify or supplement the request
If-Modified-Since: (only return object if it is newer the date
authorization: (user password or other authentication as
required)
accept: application/postscript
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HTTP Response
consists of
status line (success or failure)
HTTP/1.1 400 Bad Request
200 (Document Follow), 301 (Move Permanently), 302
(Move Temporarily), 304 (Not Modified), 401
(Unauthorized), 402 (payment required), 403
(Forbidden), 404 (Not Found), 500 (server error)
description of the information (metaheader)
Server, Date, Content-Length, Content-Type, ContentEncoded, Last Modified
actual info requested
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Content-Type: MIME Type
MIME Type
text/plain
text/html
application/postscript
application/ms-powerpoint
application/x-javascript
image/gif
image/jpeg
audio/midi
video/mpeg
x-world/x-vrml
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File Extension
txt, default (most server)
htm, html
ps
ppt
js
gif
jpg
mid
mpg
wrl
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Configure MIME Types
For supporting new mime types, both web server
and web client may need to be reconfigured.
For web server,
Include new mime.type definition in the mime.types
file of the configuration directory of the web server
By default, most servers deliver unknown type as
text/plain
browser then may display them as “gibberish”
Restart the web server
For web client,
Specify external viewer associated with the mime
type
Or, install the plug-in associate with the mime type
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Brief Survey of Web Servers
http://www.w3c.org/hypertext/WWW/Servers.
html
Jigsaw, http://www.w3c.org/Jigsaw/
http://java.sun.com/products/java-servers/
http://www.yahoo.com/computers_and_Inter
net/Internet/World_Wide_Web/HTTP/Servers
http://www.netcraft.co.uk/Survey/
“Web Server Technologies” by Nancy J.
Yeager and Robert E. McGrath, Morgan
Kaufmann 1996.
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CGI Script Example
Client type http://owl.uccs.edu/cgibin/chow/uptime.pl
or click on <A HREF =“http://owl.uccs.edu /cgibin/chow /uptime.pl”> Show the load on owl</A> in a
web page.
uptime.pl
#!/usr/bin/perl
$UPTIME = '/usr/ucb/uptime';
select(STDOUT); $| =1; #make output unbufferedprint "Content-type:
text/html\n\n";
if (-x $UPTIME) { exec($UPTIME);
} else { print "cannot find uptime command on this system.\n"; exit(1); }
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CGI Script Example (Step 2)
Web browser sends “GET /cgi-bin/chow/uptime.pl
HTTP/1.0” to owl.uccs.edu
httpd server at owl parses the request and discovers
that a perl script needs to be executed.
It locates the script in the file system.
Create the execution environment
starting a process with appropriate shell environment
variable set
with STDIN from httpd program
with STDOUT to httpd
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CGI Script Example (Step 3)
uptime.pl generates
Content-type: text/plain
15:55 up 18 days, 7:15, 5 users, load average: 0.89, 0.81, 0.79
It was sent over STDOUT back to httpd
httpd add
HTTP/1.0 200 OK
Server: Netscape-Communications/1.1
Date: Tuesday, 27-Jan-98 23:12:45 GMT
httpd relays the text string back to the web browser
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What problems can occur?
How to detect a script running infinite loop?
How to detect a hung script?
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Handle Multiple Requests
Can’t afford sequential processing, since some requested
documents are big.
Three basic approaches:
1. Fork a new child process: Cloning a copy of httpd
2. Use multithread (if the OS or language support it)
e.g., IIS, Java Web Server, Jigsaw
3. Spread the load among several helper programs
e.g., Apache
Apache allows the starting , min, max # of child web server
processes to be specified in a configuration file. It can
dynamically adjust to the load.
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More than One Web Service on the
Same Server Platform
Run different/same httpd programs on different ports
http://www.server.org/intro.html (port 80 by default)
http://www.server.org:8080/intro.html (port 8080)
http://www.server.org:8081/intro.html (port 8081)
They may have different document trees, content,
and access control, and serve different user groups
(customer, sales, authorized)
Note that running program at any port < 1024
requires root privilege.
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Virtual Hosting
To allow one server to server requests with multiple IP
addresses.
It is a low cost option for clients that want own id and cannot
afford a separate machine/connection.
Hosting other domain names on the same machine.
http://www.a.com/home.html
http://www.b.com/home.html
Require OS with virtual host support.
Assign Multiple IP numbers to the same interface
using the ifconfig command in UNIX or ipconfig in NT.
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Assign Multiple IP Address
to the Same Interface
On FreeBSD, execute
ifconfig ep0 192.168.123.2
ifconfig ep0 192.168.123.3 alias netmask 0XFFFFFFFF
ifconfig ep0 192.168.124.1 alias
(netmask option is used to suppress error msg)
On Linux, execute
ifconfig eth0:0 192.168.123.3 192.168.124.1
you may add
# route add -host 192.168.123.3 dev eth0:0
# route add -host 192.168.124.1 dev eth0:0
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New Hosting Technique
Set up virtual machines for each customer
Related software packages:
User mode Linux
VMWare ESX and Virtual Center/Infrastructure.
MS VS 2005
Utility Computing (On-Demand Computing)
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Improving WWW Delivery
Systems
Currently network is bottleneck.
The retrieval of web pages can be improved
by
increasing network bandwidth, e.g., ADSL link
reducing round trip, e.g., use client side
programming to check data with Java/Javascript
caching (both at client and proxy cache server)
increase # and processing power of web servers
load balancing by partitioning client-server
requests
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Large Web Sites
Mapping the request, e.g., ftp.netscape.com,
evenly across a set of server, e.g., ftp[128].netscape.com to Internet
RRDNS
Router/Firewall
Web
Server1
HA NFS Server
DMZ Firewall
Web
Server9
Internal
Proxy Server
HA NFS Server
Router/Firewall
To Intranet
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Web
Pages
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CISCO Distributed Director
Distributed Director
uses, the Director
Response Protocol
(DRP), a UDP-based
application for
querying DRP server
agent for BGP and
IGP routing table
metrics between
distributed servers
and clients, and
perform load
distribution.
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Internet Caching
Harvest/SQUID Cache: hierarchical, 42% ftp bw reduction
Client/Proxy Cache. Local Small, 65% bw reduction
Server Push Cache: Gwertzman and Seltzer (cornell)
Distributed Internet Cache: Povey and Harrison (uq)
hierarchical index on tree top, content on the leave
Cachemesh: Wong and Crowcroft (ucl)
cache routing table for reducing search overhead
WebWave: Heddaya and Mirdad (bu)
Cache on Route, Tree Load Balancing &Load Diffusion
Adaptive Web Caching: Zhang, Floyd, Jacobson
Self-configuration Cache Group, Multicast.
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Havest/SQUID Object
Cache
Hierarchical Cache: Danzig, Hall & Schwartz shows it
reduces 42% of FTP traffic. Place Big caches between
regional networks and backbone. Byte*hop as metric
Havest Object Cache: manual configurated hierarchical
cache system. Client uses Internet Cache Protocol
(ICP) to (recursively) query Sibling and Parent caches
NLANR SQUID Object Cache. Internet hierarchical
cache system. Problems:
14 separate Australian branches from US
CA content sources distribute content through East Coast root
cache, back to CA clients.
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Server Push Cache
Assume a network with a lot of push cache
servers.
Show server initiated cache (push cache)
can be combined with client cache to be very
effective.
Use network topology info and access
history to decide which push cach server to
place replica.
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Distributed Internet Cache
Povey and Harrison (Univ. of Queenland,
Brisbane)
Address hierarchical cache problem
Hierarchical structure for data searhing only.
with mapping info on non-leave nodes,
content on the leave.
After retrieving a new page, send
advertisment up the tree hierarchy. Nonleave node in the path store the
advertisement (url, cache loc.) in its table.
Disadvantages: increase load on leave
caches.
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Cachemesh
Wong and Crowcroft (University College London).
Client search cache routing table for cache location.
A collection of co-operating caches use Cache Information
Exchange Protocol (CIEP) to add/delete entries to the cache
routing table.
Web site as unit for cache table entries
Collision resolution when multiple cache servers claim
responsibility (based on freq.) for a web site: use random
CIEP_ADD/DELETE sending delay.
Realistic metrics to be used for selecting cache server.
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WebWave
Heddaya and Mirdad (Boston Univ.)
No directory lookup or cache search.
Cache lies along the route to the source.
Assume cache server can change filter rules
in router to intercept and server the web
requests.
Define Optimal Tree Load Balancing (TLB).
Provide load diffusion algorithms that
achieve TLB.
Only address single tree for now.
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Adaptive Web Cache
Zhang (UCLA), Floyd, Jacobson (NRG, LBNL)
New DARPA-funded research project.
Focus on scalability and self-configuration.
Self-configuration Cache Group use Cache Group
Management Protocol (CGMP).
IP Multicast delivery.
Cache server may join multiple cache groups (select
multi-homed hosts as cache server)
Ideally one cache server forward requests to the
source.
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Dynamic Server Selection
One candidate architecture
Web
Server1
Web
Server2
Web
Server8
Server push
load status
LB Agent
client
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Web
Server9
Client probe
response time
LB Agent
LB Agent
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LB Agent
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Novel Server Selection
Technique
Fei et al (Ammar) [GIT-CC-97-24]
Use application layer anycast to select the best
geographically separated web servers.
Server push (server load status) to resolver.
Only push when load change over threshold.
Client (resolver) probe (response time of the server)
Retrieve fixed size document in each server.
Avoid oscillation by returning one server from a set
of equivalent servers.
Investigate the impact of push/probe frequency on
response time.
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Application-layer Anycast
Architecture
Resolver
Server
Content
Server
Performance
Update
Push
Daemon
Probes
Probe
Client
Server Pushes
(multicast)
Probe
Update
Name
Resolver
client/server
comm.
Anycast
Query/Response
Anycast-ware
Client
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Experimental Topology
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Performance of Server Location
Scheme
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Response Time Varying
with Push and Probe
Frequency
Server push twice/min
Client Probe once/6min
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vs.
Server push 12 times/min
Client probe once/10min
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Dynamic Server Selection vs.
Load Balancing in Servers
In Fei et al’s work, after every client chooses the
lightest server, it becomes the heavy loaded server.
Next round, every client swings to next lightest
server and results in oscillation in server selection.
How to damp the oscillation:
Anycast resolvers return a set of good servers
A threshold is used to add/delete good server set
User response time vs. System throughput
Dynamic server
Load Balancing
selection
in Servers
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WAN Load Balancing
Architecture
LBed Server
Content
Server
Probes
Performance
Update
Server Pushes
(multicast)
Push
Daemon
client/server
comm.
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LB Agent
LB Agent
Probe
Client
Probe
Client
Probe
Update
Probe
Update
LB
Coordinator
LB
Coord.
Protocol
LB
Coordinator
LB
Query/Response
LB
Query/Response
LB
Client
LB
Client
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WAN Load Balancing
Architecture-2
Server
Content
Server
Probes
LB Agent
LB Agent
Probe
Client
Probe
Client
Probe
Update
Probe
Update
LB
Coordinator
client/server
comm.
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LB
Coord.
Protocol
LB
Coordinator
LB
Query/Response
LB
Query/Response
LB
Client
LB
Client
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WAN Load Balancing
Architecture-3
Server
Content
Server
Probes
client/server
comm.
LB Agent
LB Agent
Probing
module
Probe
Control
Update
Probing
Module
Probe
Control
Update
LB
Coordinator
Traffic
Update
LB
Coord.
Protocol
Traffic
Control
Load Balancing System
LB
Query/Response
LB
LB
Client
Client
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LB
Coordinator
Traffic
Update
Traffic
Control
LB
Query/Response
LB
LB
Client
Client
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Functions of LB coordinator
Collect server load, network status, and traffic status
from probing and traffic control module
Share the server and traffic status with other LB
coordinators via LB coordinating protocol
Run load balancing algorithm that
directs the client requests (macro control)
dynamically regulates the client-server traffic (micro control)
Control the probing frequency of probing module
Regulate the traffic of client-server communication
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Status Collection in WLB
system
Passive traffic monitoring on client-server
comm.
Server load report from other LB
coordinators
Active probing on server and network loads
when there is no traffic status reports
Research issues:
traffic monitoring system design
efficiency, accuracy, coordination of probing
system
derive server and network load from traffic data
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Traffic Control in WLB
System
Admission control (Macro level Control)
Estimate the load of the requests
Direct the requests
Taffic grooming/shapping (Micro level
control)
At what protocol level (TCP, IP?)
At which module/interface (Router?
Layer4/Content/Web switch)
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Important Web Sites
http://www.w3c.org/
http://developer.netscape.com/
http://java.sun.com/
http://www.microsoft.com/workshop/default.a
sp
http://www.apache.org/
http://www.netcraft.co.uk/Survey/
http://web.mit.edu/afs/athena/user/w/s/wsma
rt/WEB/HTMLtutor.html
...
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Useful References
Oreily’s Web series
HTML, CGI, Dynamic HTML, Programming Perl
“Web Server Technologies” by Nancy J. Yeager and
Robert E. McGrath, Morgan Kaufmann 1996.
HTML+CGI
World Wide Web Beyond the Basics, edit by Marc
Abrams, Prentice Hall, 1998
MS Technical Support for IIS, self learning manual.
How to setup and maintain a web sites, L. Stein.
Web Server Tuning
…
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