I was doing some testing on my server the other day, and realised that http compression within apache (httpd) was not enabled by default. Further digging showed me that mod_defate was what I needed, and infact it was installed by default on my CentOS box.
How to enable mod_default on Centos: Create /etc/httpd/conf.d/deflate.conf with the following contents
# Insert filter
SetOutputFilter DEFLATE
# Netscape 4.x has some problems...
BrowserMatch ^Mozilla/4 gzip-only-text/html
# Netscape 4.06-4.08 have some more problems
BrowserMatch ^Mozilla/4.0[678] no-gzip
# MSIE masquerades as Netscape, but it is fine
BrowserMatch bMSIE !no-gzip !gzip-only-text/html
# Don't compress images
SetEnvIfNoCase Request_URI .(?:gif|jpe?g|png)$ no-gzip dont-vary
# Don't compress already compressed stuff !
SetEnvIfNoCase Request_URI .(?:exe|t?gz|zip|bz2|sit|rar)$ no-gzip dont-vary
SetEnvIfNoCase Request_URI .pdf$ no-gzip dont-vary
# Make sure proxies don't deliver the wrong content
Header append Vary User-Agent env=!dont-vary
# Log Stuff !
# DeflateFilterNote Input input_info
# DeflateFilterNote Output output_info
# DeflateFilterNote Ratio ratio_info
# LogFormat '"%r" %{output_info}n/%{input_info}n (%{ratio_info}n%%)' deflate
# CustomLog /var/log/httpd/deflate_log deflate
restart httpd (/etc/init.d/httpd restart) and your done :-)
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