Transcript Web Servers and URLs - Computer Science at Siena College

Web Servers and URLs
And Domain Names
WWW vs. Internet
World Wide Web
Internet
• An application layer built
using the Internet
• Refers mostly to protocols
and content
• Existed before the WWW
• Refers mostly to physical
network, i.e., hardware,
computers, etc.
• Network of Network
concept
• Unique features
– http
– ftp
– Email: pop, imail, etc.
• Anything accessible via a
URL.
– TCP/IP protocol
– Packet Switching
MAC Address vs. IP Address
• On a network, a device has a unique
manufactures address.
• Via TCP/IP an IP Address is “mapped” to
specific MAC addresses, specific device.
• The IP Address is like an extended zip code
(12211-1462) that helps “find” a device on
the Internet.
IP Address vs. URL
• IP Address can only specify a device.
• A URL (uniform resource locator) specifies a
device, an application protocol, and the file
Folder
File
location of a resource.
Path
Name
• http://www.cs.siena.edu/facilities/map.jpg
Protocol
Server
Name
Subdomain
Domain
Name
TDL
Important WWW protocols
•
•
•
•
File Transfer Protocol (FTP): Early file sharing
Telnet: Early remote access
POP, SMTP, IMAP, MIME: Electronic Mail
Modern Protocols:
– Gnutella
– Bit Torrent
• Hypertext Transfer Protocol (http)
– Secure http (encrypted http)
Client-Server model of WWW
• Client: Web Browser,
i.e., Firefox
• Client connects to
Server
• Requests a web page
• Uses a URL to make the
request.
• Sends request over the
Internet.
• Server: Web Server, i.e.,
Apache.
• Daemon process
(constantly running)
listens for web page
requests.
• Responds by sending
web page (or resource)
over the Internet.
Web Servers
• Apache – Made by an open source
foundation, i.e, it’s free! 50% of the web
servers in the world.
• Microsoft IIS – 34% market share
• Google GWS – 5%
• Sun Java System – Once great…now hardly
used.
Anatomy of a Web Server (http host)
• Can be any computer. Apache can run on a PS3.
• Computer needs Internet connectivity and a
static IP address
– http://193.68.103.43
– It helps to have a domain name, but it’s not necessary
• RAM and multiple processors are important.
• FYI: Getting a static IP address is the big cost ($50/month
minimum). Most ISPs don’t give you a static IP address for
nothing.
Domain Names and DNS
• Domain Name System (DNS) refers to the
hierarchical system of servers that help give the
WWW names instead of just IP addresses.
• Essentially, it’s a globally distributed lookup table
• Look up the domain name and system tells you
the IP address.
–siena.edu  66.163.8.30
–rpi.edu  71.124.69.58
DNS Rational
• IP Address can change
– If you change your Internet service provider
– Move to a different location
– Expand your local area network
• Domain names do not have to change, just
update the DNS servers.
• More importantly, Domain names are easier
to remember and significant!
Who maintain the DNS
• ICANN: International Corporation for Assigned
Names and Numbers
– Non-profit, international, public company founded
in 1998 to make sure the Internet works globally.
• Internet Service Providers (AT&T, Time
Warner, Sprint, AOL, etc.)
• Organizations with Local Area Networks
(Siena, NYState Government, MapInfo, etc.)
Domain Name Registration
• Used to be centralized, non-profit
– Only had to pay administrative fee
– ICANN couldn’t handle the volume
• Domain Name Registration is now Commercialized:
– Company (like GoDaddy) becomes a registrar by applying
to ICANN.
• Once Registrars are approved by ICANN
– They can charge a fee for domain name registration and do
the paperwork for you
– Thus, ICANN only has to deal with a few thousand
registrars, rather than millions of customers.
Notable Registrars
• Network Solutions
– One of the first. In the early days, ICANN
exclusively outsourced operations to Network
Solutions, but then realized it should be an open
market.
•
•
•
•
GoDaddy
Yahoo
Verio
Aplus
What comes first, domain name or
web server?
Like asking, “What came first, the chicken or the egg?”
Early days (pre-2000)
• Setup a web server, test it
via its IP address and then
register a domain name.
• Then, update your local
DNS, or
• Ask your Internet Service
provider to update their
DNS.
Typical Process (post-2000)
• Register a domain with a
certified Registrar.
• Purchase web hosting
service.
• Ask your hosting service to
add your domain to their
DNS.
DNS Hierarchy
Top Level Domain (TDL) DNS…
coordinated by ICANN
centic
Stanford
edu
nysernet
UAlbany
RPI
net
com
twtelecom
St. Rose
Siena
cs
Web Hosting Revolution
• Very few organization maintain their own web
server?
• Why?
• What are the alternatives?
Web Hosting Options
Virtual Hosts
($5-50/month)
• A single computer can
run multiple instances
of web server software
• Many websites can be
hosted off of one
computer with one IP
address.
Dedicated Host
($50-???/month)
• You get your own
computer
• And IP Address
• Usually, rack-mounted
in a server farm with
thousands of other
computers.
One Web Server, Many Domains
Web Server
www. siena-space.org
www.cs.siena.edu
66.168.3.102
www.sos.siena.edu
DNS Server
public_html
sos
cs
siena-space.org
Web Server can
be configured to
resolve domain
name to specific
folder.
Sometimes called
mapping or
binding
Domain Names, TDLs and URLs
http://www.cs.siena.edu/~ebreimer/courses/csis-401-s09/index.html
Server Details
• public_html (or www) folder
– The folder that contains publically readable web pages
(and other public files)
• cgi-bin folder
– Common gateway interface binaries
– The folder that contains custom scripts and
applications
– Not really used anymore
– Toda, scripts often go right in the public_html folder.
Server Error files
• 404.html
– If a file can’t be found, you can have this web page
load by default
• 401.html
– If a file can’t be access (no privilege)
• http://en.wikipedia.org/wiki/List_of_HTTP_status_codes
Default page for folders
• http://www.siena.edu/people/faculty/
• If a URL points to a folder, you can have a page
load by default.
• index.html or default.html will load if a
specific page is not specified.
• Server can be configured so that a folder
listing will be returned if there is no index or
default page.
How websites used to be organized
• Early Days: Folder Hierarchy
– http://www.cs.siena.edu/~ebreimer/courses/csis401-s09/labs/
– With index page and Up, Down, and Next links
• http://www.w3.org/TR/html401/
• Today: Menus
– Static (~ebreimer)
– Dynamic (www.cs.siena.edu)
HTML Frames
• If we have time.
• Bad idea taken to the next level.
Dynamic Menus and Content
• Let the web server do the work.
– Part of TBLs original framework.
• URL can point to a script/program.
• Web server can run the script and output the
results
• Result is usually
– A Web Page
– Part of a Web Page (like the main menu)