The document discusses the architecture of the Apache web server. It begins with an overview of what a web server and the Apache web server are. It then covers Apache's history and architecture in detail, including its core components, how requests are handled, modules, concurrency model using persistent processes, and configuration. The document provides an in-depth technical summary of the Apache web server architecture.

1. Apache Web ServerApache Web Server
ArchitectureArchitecture
Chaitanya Kulkarni
chaitanya.kulkarni1@marist.edu
MSCS 521 23rd
April 2008
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2. What is “the web”?
A collection of cross-linked “websites”
A set of “web” technologies
The consistent use of URIs to represent
resources
HTTP, HTML, and everything built
around them
Every person's cheap’n’easy client-
server computing
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3. What is a Server?What is a Server?
A server is a computer or device on a networkA server is a computer or device on a network
that manages network resources. Mostthat manages network resources. Most
servers are dedicated. This means that theyservers are dedicated. This means that they
perform only one task rather than multipleperform only one task rather than multiple
tasks. On multiprocessing operating systems,tasks. On multiprocessing operating systems,
however, a single computer can executehowever, a single computer can execute
several programs at once. A server in thisseveral programs at once. A server in this
case could refer to the program that iscase could refer to the program that is
managing resources rather than the entiremanaging resources rather than the entire
computer.computer.
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4. What is Web Server ?
A computer program that is responsible
for accepting HTTP requests from
clients, which are known as web
browsers, and serving them HTTP
responses along with optional data
contents, which usually are web pages
such as HTML documents and linked
objects (images, etc.).
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5. A brief history of Apache (1)
First viable alternative to Netscape
Communications Corporation web
server
It is an open-source software with
cross-platform functionality.
First version was created by Robert
McCool
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6. A brief history of Apache (2)
Named Apache because:-
 Out of respect for the Native American
Indian tribe of Apache
 due to the project's roots as a set of
patches to the codebase of NCSA HTTPd
1.3 - making it "a patchy" server.
Chief competitors include Microsoft’s IIS
and Sun Java Systems Web Server
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7. A brief history of Apache (3)
Apache is used by giants like:-
 Google Web Servers
 Wikimedia
The Apache License allows for the
distribution of both open and closed
source derivations of the source code.
The name Apache is a registered
trademark.
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8. Apache Server Architecture(1)
Apache supports a variety of features,
many implemented as compiled
modules which extend the core
functionality.
These can range from server-side
programming language support to
authentication schemes.
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9. Apache Server Architecture(2)
Popular compression methods on Apache
include the external extension module,
mod_gzip, implemented to help with reduction
of the size (weight) of web pages served over
HTTP.
The core of a Apache Server implements the
basic functionality of the server. In addition it
implements a number of utility functions
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10. Core Component (1)
Following are the components of the
Apache core:
 http_protocol.c
 http_main.c
 http_request.c
 http_core.c
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11. Picture Depicting the Core Component
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12. How Requests are Handled?
(1)
URI to filename translation.
Check access based on host address, and
other available information
Get an user id from the HTTP request and
validate it
Authorize the user
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13. How Requests are Handled?(2)
Determine the MIME type of the
requested object (the content type, the
encoding and the language).
Fix-ups (for example replace aliases by
the actual path).
Send the actual data back to the client.
Log the request.
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14. Architecture of an Apache
Module
Picture Depicting Apache Module Architecture.
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15. The concept of a Handler
A handler is for Apache the action that
must be performed in some phase of
servicing the request
They are defined by modules. A module
might specify handlers for one, many or
none of the phases of the request
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16. Persistent Server Processes
‘Persistent Server Processes’ is a concept
that explains the implementation of
Concurrency in Apache.
To handle large incoming requests to website
TCP/IP servers fork a new child to handle
new incoming request from clients.
However in the situation of a busy web site
the overhead of forking a huge number of
children will simply suffocate the machine.
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17. Persistent Server Processes
contd..
To solve this problem Apache uses Persistent
Server Process.
It forks a fixed number of children, right from
the beginning. The children service incoming
requests independently (different address
spaces).
It is interesting that Apache server can
dynamically control the number of children it
forks (i.e. increasing or decreasing it), based
on current load.
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18. Picture depicting concurrency in Apache.
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19. Configure Apache Web Server
The configuration details are given at
this site .
We have to first configure the DNS.
Then configure the following file
/etc/httpd/conf/httpd.conf.
The root directory of Web server is
/etc/httpd, which is divided into three
parts.
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20. Configure Apache Web Server
contd..
The three parts are:
 /etc/httpd/conf (where configuration files
stays)
 /etc/httpd/logs (where the logs of Web
server and site accessing stay)
 /etc/httpd/modules (where the module
stays, which enables the server side
programmer to do programming in the
languages supported by Web server)
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21. Apache Usage.
Apache is primarily used to serve both static
content and dynamic Web pages on the World
Wide Web. Many web applications are
designed expecting the environment and
features that Apache provides.
Apache is the web server component of the
popular LAMP web server application stack,
alongside MySQL, and the PHP/Perl/Python
programming languages.
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22. Apache License
The Apache License is a free License
authored by Apache Software
Foundation or ASF.
It allows use of the source code for the
development of free and open-source
software as well as free software.
It is compatible only with the version 3
of GNU Public License or GPL.
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23. Reference material
Apache License
http://en.wikipedia.org/wiki/Apache_License
Apache Server Architecture
http://www.cs.ucsb.edu/~tve/cs290i-sp01/papers/Concept_Apache_A
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24. Concluding remarks
Apache Web Server has a modular
architecture. The core provides the basic
functionality and separate set of supporting
modules for handling HTTP requests.
Implicit Invocation is the architectural style.
Concurrency exists only between persistent
identical processes that service incoming
HTTP requests on the same port.
Functionality is easily changed by writing new
or editing existing modules.
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