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Made to Measure : Apache Web Server Customization

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Published on: Sunday 22nd August 1999 By: Pankaj Kamthan


Apache Web server originated from a series of "patches" to the NCSA Web server. As benchmark comparisons provided by Netcraft surveys show, its use has grown steadily over the last five years and it is the most popular Web server in use today. A comparison of features of a large number of Web servers currently in use is available at WebServer Compare. A quick overview of features of Apache is available here.

An Overview of Apache Modules

One of the key features of Apache is its "modular" architecture which makes is possible for anyone to add new functions to the server. In fact, most of the code that comes as part of the Apache distribution is in the form of modules, and can be removed or replaced. It has a generalized interface to modules that extends the functionality of the base package.

There are a large number of modules now written for Apache. Besides those included with the distribution, modules are also written to add functions not already in the code, or to do things which are needed on some sites but are not of widespread use. Some of these modules are written by Apache developers. Most of them, however, are written by other users of Apache who want to adapt its functionality for their needs.

In this article, we will look at a range of Apache modules which can be configured in the Apache server, and the range of advantages they offer. We will restrict ourselves specifically to UNIX-type and occassionally to Windows 9x/NT systems, though the basic ideas carry over to other systems.

Standard Modules

There are various modules that come with the Apache distribution. All the standard Apache modules currently shipped (provided you downloaded the source and not the binary) reside in Apache's src directory. However, only selected modules are compiled in by default. For example, mod_cgi (for invoking CGI scripts) is and mod_example (for demonstrating Apache API) is not compiled in by default. A list of standard modules, the ones that are compiled-in by default and the ones that are not compiled-in, is given in Appendix I.

Customizing Standard Modules

There are two reasons due to which you might like to customize your server:

  1. Adding a Function. You need a function that comes with the distribution but is not compiled in by default.

  2. Removing a Function. You don't need a function that comes with the distribution but it is compiled in by default. When removed, it will make the server executable smaller, and potentially reduce the load on the server host.

It is quite simple to enable or disable a standard module. All you need to do is suitably edit the Configuration file in the src directory. On UNIX-type systems, module selection lines begin with AddModule and have the format:

AddModule modules/standard/mod_name.o


# AddModule modules/standard/mod_name.o

Uncommenting/commenting will enable/disable a module on compilation.

Note the following:

Suppose you have installed a Apache binary for Windows 9x/NT systems. It comes with a selected few standard modules in form of DLLs which are kept in the  modules directory. You can obtain other module DLLs (such as for mod_perl) which you can enable by placing them in modules directory, and restarting Apache. The Windows version of Apache is configured to be able to load dynamic objects by default.

A Tour of Standard Modules

Modules reflect the features supported by Apache. Therefore, knowing the list of modules available is useful in order to take advantage of those features.

As an example, Apache supports Common Gateway Interface (CGI) scripts through the module mod_cgi, Server-Side Includes (SSI) and eXtended Server-Side Includes (XSSI) through the module mod_include, (server-side) image maps through the module mod_imap, content negotiation through the module mod_negotiation, cookies through the module mod_usertrack, URL-to-URL and URL-to-filename mapping using mod_rewrite, and correcting minor spelling errors in URL through the module mod_speling. Appendix I lists modules that can be useful for other applications.

Nonstandard Modules

There are a variety of nonstandard or "third-party" modules developed by users around the world. They can be found in the Module Registry Database.

Adding a Nonstandard Module

To add a module to Apache, you need to carry out the following steps:

  1. Obtain the module source code file and place it in the Apache src directory.

  2. Add the module definition to the Apache Configuration file.

  3. Re-compile Apache.

  4. Install the server executable and restart the server.

Obtaining Nonstandard Modules

First, you will need to download the module. Here is a CGI referral search gateway to the Apache Module Registry Database. You may separate keywords with the boolean conditionals AND and OR to control your search results. Search without parameters returns a complete listing of the database.


A selected list of nonstandard modules is given in Appendix II. Most modules come as a single of the form mod_*.c. Place this file in Apache's src/modules/extra directory. If the module comes as more than one file, (for example, the mod_php module) follow the instructions that come with the module.

Configuring Apache

Once you have obtained the module source, Apache needs to be configured so that it will compile this code. To do that, edit the Configuration file in the src directory, and add a suitable AddModule line:

AddModule modules/extra/mod_name.o

The last argument on the AddModule line is the filename of the module, with the .c replaced by .o.

After editing Configuration file, re-compile Apache by typing the following:


Finally, stop (if you are running) the server,for example, with:

kill -TERM pid

install the new HTTPD executable, and start it, for example, with:

./httpd -f /usr/local/bin/httpd

It is usually more convenient to have aliases for starting and stopping commands.

For Windows 9x/NT, after downloading a module DLL (such as for coldfusion_module), place it in the modules directory. Then edit the httpd.conf file to include the following directive:

LoadModule name_module modules/module_name.dll

and restart Apache.

A Tour of Nonstandard Modules

The power that comes with the standard modules is further enhanced by the availability (mostly free) of nonstandard modules written for various purposes by users around the world.

Arguably, the ones that are most useful from a developer's viewpoint, are embedded language interpreter modules, for example, mod_perl, which embeds the Perl language interpreter, or mod_pyapache, which embeds the Python language interpreter. They open up an entire host of new applications which have previously been nonexistent. Often scripting languages such as Perl and Python are used to write CGI scripts but tend to suffer from performance problems. With the use of corresponding modules mentioned above, one can have significant performance gain when using CGI scripts written in these languages and running them under Apache. These CGI scripts can now also access Apache internals. Besides that, one can even write Apache modules (which have traditionally written in C) in these languages. With the module mod_javascript, one can now take advantage of server-side JavaScript, which till now has only been available in Netscape FastTrack and Enterprise servers.

Apart from embedded interpreter modules, there are various other useful modules: apache_ssl, which provides Secure Socket Layer (SSL) protocol extension in Apache and makes it run as a secure server; mod_fastcgi for FastCGI, which speeds up CGI script via co-processing; and mod_auth_msql and mod_auth_mysql for authentication against mSQL and mySQL databases, respectively. Appendix II lists modules that can be useful for other applications.


One of major powers of Apache come from the pool of modules it offers. This power can be unleashed by knowing what this pool consists of, how it can be configured, and how it can be extended.


Appendix I : List of Standard Modules

This appendix (alphabetically) lists of all of the standard modules that are part of the current (version 1.3.x) Apache distribution. Table 1 the modules that are compiled-in by default and Table 2 lists the ones which are not.

mod_access Host based access control
mod_actions Filetype/method-based script execution
mod_alias Aliases and redirects
mod_asis The .asis file handler
mod_auth User authentication using text files
mod_autoindex Automatic directory listings
mod_cgi Invoking CGI scripts
mod_dir Basic directory handling
mod_env Passing of environments to CGI scripts
mod_imap The imagemap file handler
mod_include Server-parsed documents
mod_isapi Windows ISAPI extension support
mod_log_config User-configurable logging
mod_mime Determining document types using file extension
mod_negotiation Content negotiation
mod_setenvif Set environment variables based on client information
mod_status Server status display
mod_userdir User home directories
mod_unique_id Generate unique request identifier for every request
mod_usertrack User tracking using Cookies

Table 1. Apache Standard Modules Compiled-In by Default.

mod_auth_anon Anonymous user authentication, FTP-style
mod_auth_db User authentication using Berkeley DB files
mod_auth_dbm User authentication using DBM files
mod_cern_meta Support for HTTP header metafiles
mod_digest MD5 authentication
mod_example Demonstrates Apache API
mod_expires Apply Expires: headers to resources
mod_headers Add arbitrary HTTP headers to resources
mod_info Server configuration information
mod_log_agent Logging of user agents
mod_log_referer Logging of document references
mod_mime_magic Determining document types using "magic numbers"
mod_mmap_static Mapping files into memory for faster serving
mod_proxy Caching proxy abilities
mod_rewrite Powerful URI-to-filename mapping using regular expressions
mod_so Experimental support for loading modules (DLLs on Windows) at runtime (not compiled-in the UNIX distribution)
mod_speling Automatically correct minor typos in URLs

Table 2. Apache Standard Modules Not Compiled-In by Default.

Appendix II : List of Nonstandard Modules

This appendix is a list of some nonstandard Apache modules. The selection is biased towards modules for programming language support and Web site administration. See Table 3.

apache_ssl SSL extensions for Apache
mod_bandwidth Limit bandwidth based on number of connections
mod_cint Embedded C/C++ interpreter module for apache
Chili!ASP Active Server Pages module
ColdFusion Module Interface to the ColdFusion application server (Windows NT only)
Cookie Authentication Fake Basic authentication using Cookies
dir_log_module Implements per-directory logging
Distributed Permanence Control Apache Module Module designed to work with RCS and CVS to encourage the permanence of document version/editions on the Web
FastCGI Keeps CGI processes alive to avoid per-hit forks
GIF Counter Basic GIF counter
Hotwired Mod_include Hotwired extensions to mod_include
Indexer Configurable directory listing module
Java Wrapper Module Enables execution of Java applications as CGI directly
mod_allowdev Restricts access to filespace more efficiently
mod_auth_ldap Apache LDAP authentication module
mod_auth_mysql mySQL authentication module
mod_auth_udp External authentication using UDP
mod_cgisock Socket implementation of the CGI
mod_format Formats C, C++, and Java source code using HTML
mod_gunzip On-the-fly decompression of HTML documents
mod_hosts_access Allows you to use the hosts.allow and hosts.deny files to configure access to Apache
mod_javascript JavaScript module (ECMA-262)
mod_jserv Java servlet interface
mod_neoinclude NeoWebScript - Tcl scripting extension
mod_perl Embeds Perl language interpreter and provides a Perl interface to the server API
mod_ssl Free Apache interface to SSLeay
mod_weborb Directly invokes CORBA-objects to handle CGI requests
mod_auth_msql Basic authentication with the mSQL database
parselog Perl script to parse and store logs by server and date
PHP Server-side scripting language with extensive database support
mod_pyapache Embedded Python language interpreter
TalentSoft WebPlus (Web+) Web+ (WebPlus) application development tool/database middleware. Supports Linux, Apache API, mySQL, miniSQL, PostgreSQL, etc.
WebCounter Page counter

Table 3. Apache Nonstandard Modules.

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Linux #4 "Setting up DHCP is not P2C2E"

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Linux#1 A Red Hat to cover your a-- (oops!) head.

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