Ads, Analytics and cookies...

Jorge Nerín jnerin+varnish at
Fri Aug 8 23:49:00 CEST 2008

As far as I know if the backend does not change the object requested
dynamically (page source code, image, etc) using conditions that depends on
the value of cookies it is safe to be cached in varnish (or a public proxy).

You will (should) not be using third party cookies to generate different
contents, and the google analytics server and the Openx Ad server will
deffinetly be generating different content using the cookies. But the
parsing code is a javascript included in your page but (this is important)
served by their servers, so it can never be cached by varnish because the
client browser ask for it directly to the third party servers.

Greetings, hope it makes sense.

On Fri, Aug 8, 2008 at 21:20, Ian M. Evans <ianevans at> wrote:

> Okay, well, I thought I was doing the cache friendly thing by moving my
> poll only cookie to the /poll/ path (Re: Ignoring cookies except for one
> area)
> That worked, but after checking out my cookies in Firefox, I see that
> Google Analytics and the Openx Ad server toss a bunch of cookies in '/'
> for my domain. So of course a cookie is attached to each page, image,
> javascript and CSS file.
> Since I assume that some of the main sites in need of Varnish would be
> the high-traffic, digg-friendly, ad-supported, Analtyics-using sites
> what's the way around this?
>  From what I've been reading I can use the VCL rules to strip the
> cookies off the static stuff like .css and .jpg, and .js...but what
> about the dynamically-created pages?
> And how do I know where cookie stripping might hurt ad delivery?
> I didn't see anything about dealing with ad servers in the FAQ, so I
> thought I'd ask.
> _______________________________________________
> varnish-misc mailing list
> varnish-misc at

Jorge Nerín
<jnerin at>
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