We begin by downloading QOS from <a href="http://sourceforge.net/projects/mod-qos/files/" target="_blank" class="news_link" title="Download QOS">SourceForge</a>. 

 The latest version is 10.3. We will use this version for purposes of this demonstration. 


Once downloaded, untar the file like this:


<pre class="brush: bash">
tar xvfz mod_qos-10.3.tar.gz
</pre>



And then issue the following command to build the module from its source. From this point please make sure that you have root access.


<pre class="brush: bash">
cd mod_qos-10.3/apache2
apxs2 apxs -i -c mod_qos.c -lcrypto -lpcre
</pre>



apxs2 will install mod_qos.so to /usr/lib/apache2/modules. If apxs2 cannot be found/not yet in your system, install them along with other essential build tools and then reissue the apxs2 command. See below.



<pre class="brush: bash">
apt-get update
apt-get install apache2-threaded-dev build-essential
</pre>


<h3>
Installation and configuration
</h3>


Using your favorite editor, create qos.load and qos.conf in /etc/apache2/mods-available



/etc/apache2/mods-available/qos.load


<pre class="brush: bash">
# Edited 4/5/2013 
LoadModule qos_module /usr/lib/apache2/modules/mod_qos.so
</pre>



/etc/apache2/mods-available/qos.conf 



<pre class="brush: bash">
&lt;IfModule mod_qos.c>
 # Connection level
 #
 # Maximum number of active TCP connections is limited to 256:
 # (limited by the available memory, 
 # adjust the settings according to the used hardware)
 MaxClients 256
 #
 # Disables keep-alive when 70% of the TCP connections are occupied
 QS_SrvMaxConnClose 180
 #

 # Defines minimum upload/download throughput a client must generate
 # in bytes per seconds before connection is closed.
 # See comments further down below. 
 QS_SrvMinDataRate 150 1200
 #
 # Allow only 50 connection per IP address
 QS_SrvMaxConnPerIP	50

 # Block clients violating some basic rules frequently (don't allows more than 20
 # violations within 5 minutes)
 QS_ClientEventBlockCount 20 300
 QS_SetEnvIfStatus 400 QS_Block
 QS_SetEnvIfStatus 401 QS_Block
 QS_SetEnvIfStatus 403 QS_Block
 QS_SetEnvIfStatus 404 QS_Block
 QS_SetEnvIfStatus 405 QS_Block
 QS_SetEnvIfStatus 406 QS_Block
 QS_SetEnvIfStatus 408 QS_Block
 QS_SetEnvIfStatus 411 QS_Block
 QS_SetEnvIfStatus 413 QS_Block
 QS_SetEnvIfStatus 414 QS_Block
 QS_SetEnvIfStatus 417 QS_Block
 QS_SetEnvIfStatus 500 QS_Block
 QS_SetEnvIfStatus 503 QS_Block
 QS_SetEnvIfStatus 505 QS_Block
 QS_SetEnvIfStatus QS_SrvMinDataRate QS_Block
 QS_SetEnvIfStatus NullConnection QS_Block
 #
 #URL request level 
 #
 # Limit concurrent request to location /app/images to 100
 QS_LocRequestLimit /app/images	100
 #
 # Limit the download bandwidth in /app/downloads
 QS_LocKBytesPerSecLimit /app/downloads 		640
&lt;/IfModule>
</pre>



Save both files, enable qos and restart apache2.


<pre class="brush: bash">
a2enmod qos
/etc/init.d/apache2 restart
</pre>


<h4>
More on QS_SrvMinDataRate
</h4>
<div style="margin-left:35px;">

 QS_SrvMinDataRate &lt;bytes per second> [&lt;max bytes per second> [&lt;connections>]]
 defines the minimum upload/download throughput a client must generate (the bytes sent/received by the client per seconds). This bandwidth is measured while receiving request data (request line, header fields, or body), sending response data (header fields, body) and during keep-alive. The client connection is closed if the client does not fulfill this required minimal data rate and the IP address of the causing client is marked in order to be handled with low priority (see the QS_ClientPrefer directive). 


The "max bytes per second" activates dynamic minimum throughput control: The required minimal throughput is increased in parallel to the number of concurrent clients sending/receiving data (starts increasing when reaching the "connections" threshold). The "max bytes per second" setting is reached when the number of sending/receiving clients is equal to the MaxClients setting. 


The "connections" argument is used to specify the number of busy TCP connections a server must have to enable this feature (0 by default). It is used to disable the QS_SrvMinDataRate rule enforcement on idle servers.

</div>


Please be careful in setting values for QS_SrvMinDataRate. Robots/spiders could potentially be blocked.




Please visit the QOS website for a lot more options including how to configure Apache logs to include QOS statistics. There is also a documentation that comes with the tar download.



That's it. Good luck.

Install and configure Apache2 QOS module in Debian Squeeze