How do I get varnish to return in the http response header from which backend it took the response?

Question

I have three servers in the backend, with a round robin director.

I would like varnish to write a X-Server-By header with the name or ip of the server from which the response was fetched, how can this be done?

score 12 · Answer 1 · answered Jul 11 '12 at 04:42

12

In Varnish 3.0.2 I use:

sub vcl_fetch {
    set beresp.http.X-Backend = beresp.backend.name;
}

Works perfectly.

answered Jul 11 '12 at 04:42

thepearson

2

For Varnish 4, `vcl_fetch` has been renamed `vcl_backend_response`. Otherwise this works there too. – Pete Jul 31 '14 at 21:50

rossnz · Answer 2 · 2010-04-07T02:51:49.347

4

sub vcl_fetch {
    set obj.http.X-Backend = req.backend;
}

Tested on 2.0.6 in my (non round robin) setup. It should give you something to go on.

edited Apr 07 '10 at 02:51

answered Apr 07 '10 at 02:04

rossnz

1

that just displays the backend id, not the individual server – hoberion Nov 02 '10 at 11:26
In Varnish 3+ this should be: `set beresp.http.X-Backend = req.backend;`, however it will still only report the backend's id so it will not be that useful with round-robin backends. – Martijn Heemels Jul 04 '12 at 13:39
This is not the way to do it. Set the header on the backend. – Pax Jul 11 '12 at 19:13

score 3 · Answer 3 · answered Jun 17 '11 at 20:01

3

You can set the header on your web server eg x-host: server2 and then varnish will return that as part of the response to a cache hit.

I have this working on apache and it works perfectly.

answered Jun 17 '11 at 20:01

Nirav24x7

Do it this way, trying to set the header in Varnish doesn't make sense. Set it at the backend itself and Varnish will pass it on to the client. – Pax Jul 11 '12 at 19:11

score -1 · Answer 4 · answered Mar 29 '10 at 08:07

-1

The following is not tested, but might get you started:

sub vcl_deliver {
    set resp.http.X-Served-By = server.hostname;
    deliver;
}

answered Mar 29 '10 at 08:07

4 Answers4