It would be useful, for tracking down certain kinds of errors at the edge<->appserver interface, to include the Server: header from the HTTP response.
I mostly imagine using this via varnish50x logstash, although having it in webrequest tables proper doesn't seem like a bad idea either.
I've prepared https://gerrit.wikimedia.org/r/#/c/operations/puppet/+/511690/ for this. Will emitting an extra field in varnishkafka cause any problems for Analytics systems? Or will the unknown field simply be ignored?