Presented by Chris Janneck (“CJ”)
Web Servers
Web Protocols and Practice:
Chapter 4
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of Web Servers and Service
Introduction of Servers and Sites
Steps in Handling a Client Request
Sharing and Saving data across Clients
Server Architectures
Real-World Servers and Hosting
Case Study: The Apache Server
• This presentation will cover many aspects
What’s Coming Up
• A web server is the
software which posts
the site(s) on the
Internet
• Servers handle the
HTTP requests, call
any necessary scripts
or dynamic material,
etc.
• A web site is a
collection of pages,
seen by users on the
Internet
• Types of sites can
include web searches,
e-commerce sites,
personal pages, etc.
Web Site or Server: Which is it?
Provide content, or error message if suitable
4. Generate and transmit response
Does client have permission?
3. Determine authorization for request
URL != PATH
2. Translate URL to file name
Examine header, operations needed, etc.
1. Read and parse HTTP request message
Method of Handling Requests
– Authentication: determines if the client request
comes from a valid user, and which one
• Usually a username and password
• Necessary in establishing a session with the server
– Authorization: determines if the user has
permission to access/use the requested resource
• Can be established on a directory or file basis
• Divided into two parts:
Setting the Web’s “Permissions”
“static” HTML pages
• This differentiates the Web from prior file
transfer methods (e.g. FTP)
• Usually, dynamic content takes a larger toll
on the server than similar “static” pages
• The web and web servers are not limited to
Dynamic Responses
– Can include macros (directives)
• Given in file, invisible to the user
• E.g. <!-#echo var=‘ ‘LAST_MODIFIED’’->
– To alleviate unnecessary load in parsing for
includes, pages which use them are given
specific URLs
• .shtml
• .php – Personal Home Page
• .asp – Microsoft Active Server Page
• Server-Side Includes
Methods for Dynamic Response
– New process invoked by server
• CGI (Common Gateway Interface)
– Module within Web server
• Saves overhead of new processes
• NSAPI – Netscape Server API
• ISAPI – Microsoft’s Internet Server API
– External consistent process which Server
contacts
• Databases, etc.
• FastCGI
• Server Scripts
Methods for Dynamic Response
– Local scripts may access data blocked
otherwise from the outside
• Security cautions
– Dynamic content forces server to generate
internally or retrieve data, instead of simply
transmitting a static page
• Performance hit on the server
Cautions in Dynamic Content
• Security concerns with Cookies
– Retain a user’s settings in a dynamic
environment
– May contain preferences, contact info, items in
an online “shopping cart”
client host by the server
• They allow the server to retain state in the
“stateless” world of HTTP
• Cookies are simple text files placed on the
“C” is for Cookie
– The translation process, control information,
etc.
parsing through an HTML request
• Or, the server can share data involved in
– Storing content in memory decreases the time
needed to fetch/generate responses
– “server-side” caching
among similar (or identical) requests
• Servers can also share responses to requests
It’s Nice to Share
– One way, the other way, or the middle way
different clients across the internet
• Like multiprocessing, there are 3 main
approaches to this problem
• A server handles requests continually from
Server Architectures
request if the first one is idle, waiting for a
resource, disk transaction, etc.
• Works well for small, bounded sites
• Problems arise when waiting for resources
from other sites, or generating highly
dynamic pages
• Can tweak this to begin working on another
– Once the first request is handled, begin the next
• Simplest idea: handle one request at a time
One way: Event-Driven
allocate a new process to each request
• Each process completes all necessary steps
for the request, then terminates
• The entire server is not hampered if a single
process encounters a long wait
• Caution: Must be wary of memory leaks
and computational overhead of forking
• Another common computing idea is to
Other way: Process-Driven
• Multithreaded servers are another example
• Are susceptible to downsides of both styles
process to handle more than one request
simultaneously
• E.g. A process-driven style which allows each
utilizes some aspects of Event and Processdriven styles
• A Hybrid architecture is simply one which
The Middle Way: Hybrid
machine
• Can install multiple domains on the same
– http://www.me.com/two and …/three
be dedicated to web hosting
• It is possible, and often done, to host
multiple sites on a single machine
• Can have multiple sites within the same
domain name
• For most sites, a machine does not need to
What really happens on Servers
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harshly when hosted on a single machine
These sites can have their content hosted on
many machines to help with traffic
Often called “mirror” sites
Mirrors can replicate the whole site, or large
files (video, audio, hi-res pics, etc.)
Make sure data is up-to-date on all
machines
• Larger, more popular sites will suffer
And then, there was Yahoo!
started, can place limits on number allowed
• Resources: A “resource pool” metaphor
• Each process adds, removes, and uses the
“pool” through the API
• Architecture: Process-driven
• Parent process pre-forks processes when
Case study of “A Patchy” Server
access file
3. Identify and invoke a handler to generate
response
4. Transmit response to client
5. Log the request
1. Convert the URL into a file name
2. Determine if request has permission to
Apache Handling (This side up)
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Difference between a Server and a Site?
Process in handling a client?
Sharing data and caching?
This way or that? (Event or Process-driven)
How to get the most from your machine?
Do I use Apache server or not?
Did You Get All That?
Questions?
Thank you!