Phoenix Varnish Vcl configuration

Question

we're using this varnish module http://www.magentocommerce.com/magento-connect/pagecache-powered-by-varnish.html V 3.1.2. With this module comes a default.vcl which really works well out of the box, but there is a part of the sub deliver that I don't get.

When an html object is cacheable, the sub fetch sets http.magicmarker=1

Here's what happens in the sub deliver :

if (resp.http.magicmarker) {
    # Remove the magic marker
    unset resp.http.magicmarker;

    set resp.http.Cache-Control = "no-store, no-cache, must-revalidate, post-check=0, pre-check=0";
    set resp.http.Pragma = "no-cache";
    set resp.http.Expires = "Mon, 31 Mar 2008 10:00:00 GMT";
    set resp.http.Age = "0";
}

Is there a reason to set Cache-Control and Pragma to "no-cache" ?

Here is the full vcl provided with the module : https://gist.github.com/ashsmith/5429365/raw/07f047d679edfdca0a52a62b606e2dd871c360a4/default_3.0.vcl

Thank you for your help

Answer 1

I have written a Varnish module for Magento, and I assume the author of the VCL is wanting to get the browser to fetch the page each time it is requested, rather than storing a copy of it in the users web browser cache. The VCL is caching the HTML, but instructing the browser not to. A good reason for this is that you want a website to load quick, but you don't want stale or out of date information.

Answer 2

This just makes sure that Content with Content-Type ~ "text/html" or Content-Type ~ "text/xml" do not end up in the browser cache. If you go to the page a second time or you reload it, the html is always taken from varnish again. So if you call http://www.code4business.de/projekte/ the second time and you look at your network (press F12 in Chrome or Firefox with Firebug, the Network) you see this:

Everything comes from the browser cache (not Varnish) except for the html-page. This is what the underneath code is doing. It might be useful is some cases. However, I would hope that your CMS handles it correctly already.

if (resp.http.magicmarker) {
    # Remove the magic marker
    unset resp.http.magicmarker;

    set resp.http.Cache-Control = "no-store, no-cache, must-revalidate, post-check=0, pre-check=0";
    set resp.http.Pragma = "no-cache";
    set resp.http.Expires = "Mon, 31 Mar 2008 10:00:00 GMT";
    set resp.http.Age = "0";
}