Okay: I've got a site set up which has some APIs we expose to developers, which are in the format

/api/item.xml?type_ids=34,35,37&region_ids=1000002,1000003&key=SOMERANDOMALPHANUM

In this URI, type_ids is always set, region_ids and key are optional.

The important thing to note is that the key variable does not affect the content of the response. It is used for internal tracking of requests so we can identify people who make slow or otherwise unwanted requests.

In Varnish, we have a VCL like this:

if (req.http.host ~ "the-site-in-question.com") {
  if (req.url ~ "^/api/.+\.xml") {
    unset req.http.cookie;
  }
}

We just strip cookies out and let the backend do the rest as far as times are concerned (this is a hackaround since Rails/authlogic sends session cookies with API responses).

At present though, any distinct developers are basically hitting different caches since &key=SOMEALPHANUM is considered as part of the Varnish hash for storage. This is obviously not a great solution and I'm trying to work out how to tell Varnish to ignore that part of the URI.