X-Varnish
Varnish-generated transaction ID for a request or response.
Fastly writes this header into requests and responses. It is proprietary to Fastly.
Fastly cache servers run software derived from the open sourceVarnish caching daemon. Each time a request is forwarded through a Varnish process, it will append a transaction ID in the form of anX-Varnish header. Due to the effects ofclustering andshielding, there can often be up to four of these attached to a request when it arrives at a backend server.
It is not possible to correlate the identifier with any other customer-visible data, but these IDs can occasionally be used as part of joint debugging activity with Fastly engineers. To remove them, unset the header invcl_miss andvcl_pass:
unsetbereq.http.X-Varnish;