Adding Modules to Your Server

Since Apache 1.3 supports DSOs, you can easily load Apache modules or compile in your own modules to your Web server. DSO support means that modules may be loaded at runtime. Since the modules are only loaded as necessary, they will not use any memory unless they are loaded and less memory will be needed overall.

The Apache Group provides complete DSO Documentation at http://httpd.apache.org/docs/dso.html. After installation of your server, you can also check http://your_domain/manual/mod/ for documentation on Apache modules in HTML format (if you installed the apache-manual package). A short description of how to load modules is provided next. If you need more details, check the URLs provided.

For Apache to use a dynamically shared module, that module must have a LoadModule line and an AddModule line in httpd.conf. By default, many modules have these two lines already included in httpd.conf, but a few of the less commonly used modules are commented out. The commented out modules were included during compilation, but they are not loaded by default.

If you need to use one of those non-loaded modules, look in the httpd.conf file to see all the available modules. Each of the available modules has a corresponding LoadModule line. To show you an example, the LoadModule section begins with these seven lines:

#LoadModule mmap_static_module modules/mod_mmap_static.so
LoadModule vhost_alias_module modules/mod_vhost_alias.so
LoadModule env_module         modules/mod_env.so
LoadModule config_log_module  modules/mod_log_config.so
LoadModule agent_log_module   modules/mod_log_agent.so
LoadModule referer_log_module modules/mod_log_referer.so
#LoadModule mime_magic_module  modules/mod_mime_magic.so

Most of the lines are not commented out, indicating that each associated module was compiled in and is loaded in by default. The first line is commented out, which means that the corresponding module (mmap_static_module) was compiled in but not loaded.

To make Apache load an unloaded module, first uncomment the corresponding LoadModule line. For example, if you wanted to make Apache load in the mime_magic_module, uncomment this line:

#LoadModule mime_magic_module modules/mod_mime_magic.so

Next, you need to uncomment the corresponding line from the AddModule section in httpd.conf. To continue with our previous example, uncomment the mod_mime_magic line, which looks like the following:

#AddModule mod_mime_magic.c

Once you have uncommented the LoadModule and AddModule lines for the module that you want to load in, stop and start Apache, as covered in the section called Starting and Stopping httpd. After starting, the module should be loaded in to Apache.

If you have your own module, you can add it to the httpd.conf file so that it is compiled in and loaded as a DSO. If you want to do this, you need to install the apache-devel package, as covered in Chapter 13. You need the apache-devel package because it installs the include files, the header files and the APache eXtenSion (APXS) support tool. APXS uses the include files and the header files to compile your module so that it will work with Apache.

Warning

If you plan to use the Apache Configuration Tool, a GUI utility provided with Red Hat Linux, you must not compile your own modules to your Apache Web server or edit your Apache Web server's httpd.conf configuration file. Conversely, if you want to add modules to Apache or edit httpd.conf by hand, do not use the Apache Configuration Tool. If you need more information on the Apache Configuration Tool, please see the Official Red Hat Linux Customization Guide.

If you have written your own module or are borrowing someone else's, you should be able to use APXS to compile your module sources outside the Apache source tree, without needing to tweak any compiler and/or linker flags. If you need more information on APXS, please see the Apache documentation at http://httpd.apache.org/docs/dso.html.

Once you have compiled your module using APXS, put your module into /usr/lib/apache. Then your module needs both a LoadModule line and an AddModule line in the httpd.conf file, just as described previously for Apache's own modules. After the LoadModule list in httpd.conf, add a line for the shared object file for your module like the following:

LoadModule foo_module 	modules/mod_foo.so

Note that you will need to change the name of the module and the name of your shared object file as appropriate.

At the end of the AddModule list in httpd.conf, add a line for the source code file for your module like the following:

AddModule mod_foo.c

Note that you will need to change the name of the source code file as appropriate.

Once you have completed the previous steps, stop and start your Web server as outlined in the section called Starting and Stopping httpd. If you have done everything correctly and your module is correctly coded, your Web server should find your module and load it in as it starts.

The mod_ssl Security Module

The mod_ssl security portion of the Web server is provided as a Dynamic Shared Object (DSO). This means that the Apache Web server can be re-compiled by users if the EAPI extension patch from the mod_ssl security module is applied to Apache. Follow the instructions for building mod_ssl into Apache included with the mod_ssl documentation, but add the following flag:

--with-eapi-only

The complete command line should look like the following:

./configure [userflags] --with-eapi-only

Then build and install Apache.

	Note
	Red Hat cannot support re-compiled versions of the Apache Web server. Installation of the shipped version is supported, but if you re-compile Apache, you are on your own. Please do not re-compile Apache unless you know exactly what you are doing.