# If behind another Fastly service, don't keep stale objects in cache
# otherwise we might serve a stale object to a Fastly service which
# will then treat it as a fresh response from origin.  The Fastly-FF
# header lists Fastly POPs that have seen this request prior to the 
# current one.
if (req.http.Fastly-FF) {
  set req.max_stale_while_revalidate = 0s;
  set req.max_stale_if_error = 0s;
}