Varnish Cache is a web application accelerator also known as a caching HTTP reverse proxy (video).  We utilize it to help speed up your pages as well as help keep our infrastructure running in case your site starts receiving a large amount of traffic to your site.  We can serve more requests with the same hardware.

When you make content updates to your site, our varnish plugin will detect the changes and let the varnish server know that the page need to be recached.  In the event that you make changes to your site that are not automatically reflected.  When you are logged in you will see an option in the top admin menu bar called “Varnish Cache”.  Here you can purge the entire cache for your site, for a section, or for a specific page.

Purge All

This will tell varnish to invalidate all cached pages for your site.

Purge Page

This will tell varnish to invalidate just the page your are visiting.

Purge Section

This will tell varnish to invalidate all pages under the section of the site you are in.  This is performed by the URL of the site.  So if you are on a page with the URL of http://mysite.umichsites.org/section/subsection/page/  Then every page that starts with the URL of http://mysite.umichsites.org/section/ will be invalidated.

What Is Not Cached in Varnish

• Logged In Requests
  If you are logged in you will never receive a cached version of the page.  This is mainly for security reasons.  So to verify the rest of the world has seen your latest changes you will need to do one of the following:
  • Log out
  • Open the site in an Incognito Window (Chrome)
  • Open the site in another browser where you are not logged in.
• Form submissions
• Files (images, PDFs, Office Docs, etc)