How can I get Apache gzip compression to work?

First of all go to apache/bin/conf/httpd.conf and make sure that mod_deflate.so is enabled.

Then go to the .htaccess file and add this line:

SetOutputFilter DEFLATE

This should output all the content served as gzipped, i have tried it and it works.

Try this :

####################
# GZIP COMPRESSION #
####################
SetOutputFilter DEFLATE
AddOutputFilterByType DEFLATE text/html text/css text/plain text/xml application/x-javascript application/x-httpd-php
BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0[678] no-gzip
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
BrowserMatch \bMSI[E] !no-gzip !gzip-only-text/html
SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-gzip

It is better to implement it as in the snippet below.

Just paste the content below in your .htaccess file, then, check the performance using: Google PageSpeed, Pingdom Tools and GTmetrics.

# Enable GZIP
<ifmodule mod_deflate.c>
AddOutputFilterByType DEFLATE text/text text/html text/plain text/xml text/css application/x-javascript application/javascript
BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0[678] no-gzip
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
</ifmodule>

# Expires Headers - 2678400s = 31 days
<ifmodule mod_expires.c>
  ExpiresActive On
  ExpiresDefault "access plus 1 seconds"
  ExpiresByType text/html "access plus 7200 seconds"
  ExpiresByType image/gif "access plus 2678400 seconds"
  ExpiresByType image/jpeg "access plus 2678400 seconds"
  ExpiresByType image/png "access plus 2678400 seconds"
  ExpiresByType text/css "access plus 518400 seconds"
  ExpiresByType text/javascript "access plus 2678400 seconds"
  ExpiresByType application/x-javascript "access plus 2678400 seconds"
</ifmodule>

# Cache Headers
<ifmodule mod_headers.c>
  # Cache specified files for 31 days
  <filesmatch "\.(ico|flv|jpg|jpeg|png|gif|css|swf)$">
  Header set Cache-Control "max-age=2678400, public"
  </filesmatch>
  # Cache HTML files for a couple hours
  <filesmatch "\.(html|htm)$">
  Header set Cache-Control "max-age=7200, private, must-revalidate"
  </filesmatch>
  # Cache PDFs for a day
  <filesmatch "\.(pdf)$">
  Header set Cache-Control "max-age=86400, public"
  </filesmatch>
  # Cache Javascripts for 31 days
  <filesmatch "\.(js)$">
  Header set Cache-Control "max-age=2678400, private"
  </filesmatch>
</ifmodule>

Your .htaccess should run just fine; it depends on four different Apache modules (one per each <IfModule> directive). I guess one of the following:

• your Apache server doesn't have either mod_filter, mod_deflate, mod_headers and/or mod_setenvif modules installed and running. If you can access the server config, please check /etc/apache2/httpd.conf (and the related Apache config files); otherwise, you can see which modules are loaded via phpinfo(), under the apache2handler section (see attached image); (EDIT) OR, you can open a terminal window and issue the command sudo apachectl -M that will list the loaded modules;

• if you get an http 500 internal server error, your server may not be allowed to use .htaccess files;

• you are trying to load a PHP file that sends its own headers (overwriting Apache'sheaders), thus "confusing" the browser.

In any case, you should double-check your server config and error logs to see what's going wrong. Just to be sure, try to use the fastest way suggested here in Apache docs:

AddOutputFilterByType DEFLATE text/html text/plain text/xml

and then try to load a large textfile (preferably, clean your cache first).

(EDIT) If the needed modules are there (in the Apache modules dir) but aren't loaded, just edit /etc/apache2/httpd.conf and add a LoadModule directive for each one of them.

If the needed modules aren't there (neither loaded, nor in the Apache modules directory), I fear that the only option is reinstalling Apache (a complete version).