Cache with Varnish based on host only

Question

I would like to pass cookies to the backend but I don't want them to be added to the hash table. My goal is to serve each request based on its host only. Is it possible?

Answer 1

By default varnish caches based on url and host or ip if the host header is not set - see built-in vcl_hash:

sub vcl_hash {
    hash_data(req.url);
    if (req.http.host) {
        hash_data(req.http.host);
    } else {
        hash_data(server.ip);
    }
    return (lookup);
}

If you do not unset the cookies in the vcl_recv function then by default varnish does not cache the response as it will "return (pass);" in the built-in vcl_recv function.

sub vcl_recv {
  ...
    if (req.http.Authorization || req.http.Cookie) {
        /* Not cacheable by default */
        return (pass);
    }
    return (hash);
}

If you do not want to cache then this would be fine.

If you do want to cache and need to sent the cookies to the backend then I guess you have to "return (hash);" in your version of "vcl_recv" but this would only make sense if the response is always the same irrespective of the cookies sent.

As a side note: If you do want to cache the response then you will also need to unset the Cookies set by the backend or avoid to get into the built-in "vcl_backend_response"