Jul 082013
 

mod_pagespeed improves website performance and reduces page load time. This Google open-source Apache/Nginx web server module automatically applies web performance best practice to pages, and associated assets (CSS, JavaScript, images) without requiring modification of the application environment.

How does mod_pagespeed speed up web-sites?

From the Pagespeed project website: mod_pagespeed improves web page latency and bandwidth usage by changing the resources on that web page to implement web performance best practices. Each optimization is implemented as a custom filter in mod_pagespeed, which are executed when the Apache HTTP server serves the website assets. Some filters simply alter the HTML content, and other filters change references to CSS, JavaScript, or images to point to more optimized versions.

mod_pagespeed implements custom optimization strategies for each type of asset referenced by the website, to make them smaller, reduce the loading time, and extend the cache lifetime of each asset. These optimizations include combining and minifying JavaScript and CSS files, inlining small resources, and others. mod_pagespeed also dynamically optimizes images by removing unused meta-data from each file, resizing the images to specified dimensions, and re-encoding images to be served in the most efficient format available to the user.

mod_pagespeed ships with a set of core filters designed to safely optimize the content of your site without affecting the look or behavior of your site. In addition, it provides a number of more advanced filters which can be turned on by the site owner to gain higher performance improvements.

mod_pagespeed can be deployed and customized for individual web sites, as well as being used by large hosting providers and CDN’s to help their users improve performance of their sites, lower the latency of their pages, and decrease bandwidth usage.

Mod_Pagespeed Installation

wget wget https://dl-ssl.google.com/dl/linux/direct/mod-pagespeed-stable_current_i386.rpm

rpm -U  rpm -U mod-pagespeed-stable_current_i386.rpm

see here: http://linuxdrops.com/speed-up-apache-using-mod_pagespeed-module-from-google-on-centos-rhel-fedora-debian-ubuntu/

Apache Virtual Host Configuration

Jeremy Edgell provides the  following Drupal 7 oriented virtual host configuration which can be tailored to local requirements:

<IfModule pagespeed_module>

AddOutputFilterByType MOD_PAGESPEED_OUTPUT_FILTER text/html

ModPagespeed on

ModPagespeedLowercaseHtmlNames on

ModPagespeedEnableFilters extend_cache

ModPagespeedEnableFilters insert_dns_prefetch

#

# Text / HTML

#

ModPagespeedEnableFilters collapse_whitespace

ModPagespeedEnableFilters convert_meta_tags

ModPagespeedEnableFilters remove_comments

ModPagespeedEnableFilters elide_attributes

ModPagespeedEnableFilters trim_urls

ModPagespeedEnableFilters pedantic

#

# JavaScript

#

ModPagespeedEnableFilters combine_javascript

ModPagespeedEnableFilters canonicalize_javascript_libraries

ModPagespeedEnableFilters rewrite_javascript

# Risk   ModPagespeedEnableFilters defer_javascript

ModPagespeedEnableFilters inline_javascript

#

# CSS

#

ModPagespeedEnableFilters rewrite_css

ModPagespeedEnableFilters combine_css

ModPagespeedEnableFilters move_css_to_head

ModPagespeedEnableFilters inline_css

ModPagespeedEnableFilters inline_import_to_link

ModPagespeedEnableFilters move_css_above_scripts

#

# Images

#

ModPagespeedEnableFilters inline_preview_images

ModPagespeedEnableFilters insert_img_dimensions

ModPagespeedEnableFilters rewrite_images

ModPagespeedEnableFilters recompress_images

ModPagespeedEnableFilters convert_jpeg_to_progressive

ModPagespeedEnableFilters resize_mobile_images

ModPagespeedEnableFilters sprite_images

ModPagespeedEnableFilters lazyload_images

# Risk   ModPagespeedEnableFilters local_storage_cache

</IfModule>

Mod_Pagespeed Accelerator Configuration

Varnish/Nginx Caches use cache headers to improve performance and these are modified by default by mod_pagespeed. In order to allow these accelerators to cache the mod_pagespeed generated files the following configuration option should be included in the virtual host configuration

<IfModule pagespeed_module>

ModPagespeedModifyCachingHeaders off

</IfModule>

Documentation related to this option can be found here, background information explaining why mod_pagespeed disables caching can be found here.

Preserving HTML caching headers

From the project website: “… By default, mod_pagespeed serves all HTML with Cache-Control: no-cache, max-age=0 because the transformations made to the page may not be cacheable for extended periods of time.

If you want to force mod_pagespeed to leave the original HTML caching headers you can add:

ModPagespeedModifyCachingHeaders off

Note: We do not suggest you turn this option off. It breaks mod_pagespeed’s caching assumptions and can lead to unoptimized HTML being served from a proxy caches set up in front of the server. If you do turn it off, we suggest that you do not set long caching headers to HTML or users may receive stale or unoptimized content. …”

Disabling Mod_Pagespeed

To disable mod_pagespeed for a specific virtual host include the following directive in the virtual host configuration:

<IfModule pagespeed_module>

ModPagespeed off

</IfModule>

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