Mod_pagespeed installed but filters not running on page. No pagespeed headers present

I’ve just started a standard LAMP DigitalOcean droplet and installed Google Pagespeed. The package is installed and listed in /etc/apache2/mods-enabled/

I have added the following items to the pagespeed.conf

ModPagespeedEnableFilters prioritize_critical_css                   
ModPagespeedEnableFilters lazyload_images,inline_preview_images,insert_image_dimensions
ModPagespeedEnableFilters resize_mobile_images,insert_image_dimensions

Which I have used on previous projects. For some reason none of these filters are being run. Inspecting the headers being passed from the server show no pagespeed headers.

I don’t seem to be running across any errors anywhere and I am stuck as to what to look for next.


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Accepted Answer

It turns out it was the CMS I am using. It uses the register_shutdown_function from php which with a call back introduces no-pragma and breaks pagespeed

After enabling the mod with a2enmod pagespeed did you ensure that you restarted the apache process with service apache2 restart?

In some instances mod_expires is also required in order to use mod_pagespeed. It can be enabled with a2enmod expires; service apache2 restart