Apache Modules: Understanding and Using Advanced Apache Modules

Technology has given us a lot of transformation, gifting us with some groundbreaking applications that bring out the best in customers and businesses. One widely-known web server that surprises us with recognized flexibility is Apache (also known as Apache HTTP Server).

The outstanding Apache Modules list realize its importance in the tech-driven world that brings in some greater customization capacity for server into the play.

With the great range of Apache Modules, the list of modules begins from basic to groundbreaking, allowing the administrator to extend Apache customization capabilities to another level.

Apache modules are the list of libraries that allow you to enhance the functionalities of the server and better the performance and security.

This allows you to integrate some exceptional features like caching, authentication, rewriting URLs, and so on. As a result, you can improve the application performance with ease.

However, the list of modules is exceptional, but you do not want to get your play on modules that slow down the applications.

That is why we have gathered the list of modules in the article that enable you to drive a well-optimized service to clients. Continue reading the article to explore the list of best Apache Modules list.

What are Apache Modules?

A Apache module extends the functionality of the Apache web server software. Adding new features, improving security, and optimizing performance are some of their functions.

During execution of Apache, Apache modules and PHP are loaded dynamically by the server using the C programming language. Activation and installation of them can be performed by an Apache server administrator at any time.

Dominating list of Apache modules

There is no doubt that the Apache modules in Linux is known for its flexibility. Modularity is an integral part of Apache’s implementation. With the modules, Apache is able to perform additional tasks.

As a result, the modules extend the capabilities of the Apache server. By adding or removing modules, an administrator can configure Apache easily. The Apache server comes with a set of pre-installed modules. Below is a list of commonly used Apache modules.


Apache’s mod_security module is a common one. As its name suggests, it focuses on server security. Servers can be protected from various attacks using Mod_security.

A regular expression and rule set are used to block attacks. In essence, it works as a firewall. As an embedded or reverse proxy, it could be used in either case.

Clients use reverse proxy servers to access servers on their behalf. Rather than retrieving the resources from the original servers, they return them through the proxy server.

When it comes to blocking SQL injection attacks, Mod_security is very effective. SQL injection attacks return a 406 error when they are complete.

The SQL injection attack: A SQL injection attack involves a hacker injecting SQL commands into an SQL statement via a web page input. The name of this attack indicates that it targets your database.


The mod_rewrite program is also widely used in web hosting. It is used to redirect URLs and rewrite them in order to achieve redirection. Rewrite engines in the module rewrite requests based on PCRE regular expressions.

Mod_rewrite uses an unlimited number of rules. A rule can be attached with unlimited rule conditions, enabling it to be rewritten based on variables in the server environment, HTTP headers, and other data.

Below is an example of a redirect rule for a url that starts with ‘http’ to ‘https’.

RewriteEngine On

RewriteCond %{HTTPS} off

RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

Here’s how mod_rewrite works.


It is time for us to look at the mod_deflate Apache module. Using this module, the webserver’s output is compressed before being sent to the client.

In order to make the download of the output file faster for the client, this is used to reduce its size.

Using this directive, you will be able to compress documents in the container where the documents are located.

SetOutputFilter DEFLATE

Using Apache as a reverse proxy and decompressing content passing through the proxy is also possible using mod_deflate. Although rarely used, mod_deflate is commonly used to compress web server output.

By combining LZ77 algorithm and Huffman coding, mod_deflate creates compressed files. As a result, no data is lost during the compression process.

During the modification process of mod_deflate, the output file will have a size greater than 120 bytes (approximately).

In this case, the file size of the module is not constrained by a lower bound. Mod_gzip works similarly to mod_deflate.


In Apache, the mod_cache module is responsible for caching content. Now let’s examine this module in more detail.

By using web caching, you can improve the performance of your server. Clients can access the data faster and do not need to retrieve the data each time they request a request since the frequently requested content will be stored in easy-to-access locations.

By creating caching rules, we can make caching more effective. In contrast, highly dynamic content will be delivered normally from the server to the client.

Apache also uses other methods for caching web pages, including the mod_file_cache module.


Next, we will examine the mod_proxy module. An Apache module that is optional. An Apache proxy, gateway is implemented in this module.

The system supports a number of commonly used protocols as well as a number of load balancing algorithms. On the server, a set of modules must be loaded to enable this feature. Among them are the following.

  • mod_proxy
  • mod_proxy_balancer (if load balancing is required, you will also require one or more balancer modules).
  • At least one proxy scheme module


Mod_ssl is also an optional Apache module. Apache versions 1.3 and 2 use it. With OpenSSL, it supports Secure Sockets Layer (SSL) and Transport Layer Security (TLS). It was originally developed for Apache 3 in 1998.

The purpose of this module is to provide the Apache server with SSL v3 and TLS v1.x support. There is no longer support for SSL v2.

These are some of the most popular Apache modules.

How To Check Which Apache modules are enabled

The following steps will show you how to check whether Apache modules are enabled.

1. List the Apache modules

Using apache2ctl -M, you can list all installed/enabled Apache modules. The Apachectl command is a linux command for controlling the Apache server. Additionally, it can be used to start and stop servers.

Using a terminal, run the following command to see all modules that have been enabled for Apache.

$ apache2ctl -M
Loaded Modules:
core_module (static)
so_module (static)
watchdog_module (static)
http_module (static)
log_config_module (static)
logio_module (static)
version_module (static)
unixd_module (static)
access_compat_module (shared)

Alternatively, you can try any of the following commands if the above doesn’t work on your system

————— On Debian based systems —————
$ apache2ctl -t -D DUMP_MODULES

————— On RHEL based systems —————
$ apachectl -t -D DUMP_MODULES
$ httpd -M

2. The Apache modules you need to check

This command lists all the Apache modules that have been installed. Having many modules can create a long output list, making it difficult to locate the module you need. Using grep, you can search for the desired Apache module in the output of apachectl -M if you need one

Use the following command to see if mod_rewrite is enabled, for example

$ apache2ctl -M | grep rewrite
rewrite_module (shared)

Choosing the right multiprocessor module

A multi-processing module, or MPM, extends Apache’s modular functionality in a number of ways. A very important aspect of MPMs is that they enable clients to process their requests through the use of children processes and threads.

At the time you build your Apache server, you will have to select an MPM for it; which MPM you should select depends on the needs of the server. You generally have three MPM options, some of which are platform-specific:

There are several child processes in the worker MPM, all of which have multiple threads. Each thread handles connections one at a time.

The MPM can handle multiple concurrent connections while using less RAM than other MPMs, so it’s perfect for servers with a lot of traffic.

It is common for Apache installations to use the event MPM, which is the default MPM. Each child process is handled by multiple threads, just like the worker MPM.

In idle connections, however, a single thread handles them. Hence, new connections are possible on a larger number of threads.

Event MPM has the disadvantage that it is not compatible with Apache modules such as mod_php which aren’t thread-safe. If you use alternatives like PHP-FPM or mod_itk, you can sometimes resolve such compatibility issues.

Multiple child processes are employed by the prefork MPM, but each one has only one thread. One connection is handled at a time.

Therefore, prefork has a larger memory footprint than the other MPMs, but can be freely used with third-party Apache modules that are not thread-safe. Some platforms benefit from the threadless design by making debugging easier.

Running the necessary code from your shell will reveal which MPM is installed if the Apache server is already configured.


With this useful list of Apache Modules, you can utilize them in the best way to automate business growth with top level development.

Hopefully, you now have a better understanding of some of the modules available to modify Apache’s standard behavior.

The more code you add to a server, the greater the risk that you will expose vulnerabilities and add to its overhead. Hire web developers in India and leverage Apache Modules for next level development.

About the Author!

Albert Smith is Digital Marketing Manager at Hidden Brains, a leading software development company specializing in mobile & web apps. He provides innovative ways to help tech companies, startups and large enterprises build their brand.

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