Enable Gzip Compression On Apache HTTP Server
Enable Gzip Compression On Apache HTTP Server
March 30, 2019

In this tutorial, we will discuss the steps required to enable Gzip compression of static resources served by the Apache HTTP Server. When the browser or HTTP client sends a request to web server, the web server either generate the response(HTML) or locate the resource i.e. image, JavaScript, CSS and try to compress where possible before replying back to the browser or HTTP client. This is where Gzip compression happens where the web server further compresses the resources before sending it to the requestor.

The deflate output filter available in the mod_deflate module does the heavy lifting job to compress and serve the static resources including HTML, images, JavaScript, CSS, etc.

Check Module

Though the module is enabled by default in Apache, we can always check whether it's available as shown below.

# Debian
apache2ctl -t -D DUMP_MODULES
apache2ctl -t -D DUMP_MODULES | grep deflate

# CentOS
httpd -t -D DUMP_MODULES

# The above commands will print the modules enabled in current installation of Apache Server
# To confirm whether Gzip is enabled, deflate_module should be there on the modules list

# It can be enabled on Debian
a2enmod deflate

On WAMP installation, it's disabled by default. It looks like the one shown in Fig 1 using System Tray. Click on the deflate_module option to enable it.

Deflate Module

Fig 1

Also, check the apache configuration file to make sure that the module is enabled.

# Locate the file httpd.conf and make sure that it is enabled.

# Ebabled - All is well
LoadModule deflate_module modules/mod_deflate.so

# Disabled - Remove # and save the file to enable it
# LoadModule deflate_module modules/mod_deflate.so

Gzip Compression

The simplest form to enable Gzip compression is to add below-mentioned line to the .htaccess file.

# Enable Gzip compression for html, text, xml, css, and javascript
AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css text/javascript application/javascript

We can also update the virtual host as shown below. In the case where it's not possible to update the virtual host, we can always go with the .htaccess option.

<Directory "/site">

# Enable Gzip compression for html, text, xml, css, and javascript
AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css text/javascript application/javascript


The complete solution is as shown below. We can also configure a few more parameters to further enhance the compression by playing with the deflate_module options including DeflateCompressionLevel, DeflateMemLevel, and DeflateWindowSize.

<IfModule mod_deflate.c>
# Compress HTML
AddOutputFilterByType DEFLATE text/html

# Compress Text
AddOutputFilterByType DEFLATE text/plain

# Compress CSS
AddOutputFilterByType DEFLATE text/css

# Compress JavaScript
AddOutputFilterByType DEFLATE application/javascript
AddOutputFilterByType DEFLATE text/javascript
AddOutputFilterByType DEFLATE application/x-javascript

# Compress Images
AddOutputFilterByType DEFLATE image/svg+xml
AddOutputFilterByType DEFLATE image/x-icon

# Compress Fonts
AddOutputFilterByType DEFLATE application/vnd.ms-fontobject
AddOutputFilterByType DEFLATE application/x-font
AddOutputFilterByType DEFLATE application/x-font-opentype
AddOutputFilterByType DEFLATE application/x-font-otf
AddOutputFilterByType DEFLATE application/x-font-truetype
AddOutputFilterByType DEFLATE application/x-font-ttf
AddOutputFilterByType DEFLATE font/opentype
AddOutputFilterByType DEFLATE font/otf
AddOutputFilterByType DEFLATE font/ttf

# Compress XML
AddOutputFilterByType DEFLATE application/rss+xml
AddOutputFilterByType DEFLATE application/xhtml+xml
AddOutputFilterByType DEFLATE application/xml
AddOutputFilterByType DEFLATE text/xml

  # Old browser fixes
  BrowserMatch ^Mozilla/4 gzip-only-text/html
  BrowserMatch ^Mozilla/4\.0[678] no-gzip
  BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
  Header append Vary User-Agent

This is the easiest way to enable Gzip compression of websites hosted on Apache HTTP Server.

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