varnishncsa %s in backend mode: 304 logged as 200

[Guillaume Quintard]

Hi,

Varnish automatically transforms the 304 response into the object it
represents, this is why you are seeing the 200 (but it could be pretty much
any status that you are revalidating).
If you want to check for 304s, you can do something like this:

sub vcl_backend_response {
    if (beresp.was_304) {
        std.log("true_status: 304");
    } else {
        std.log("true_status: " + beresp.status);
    }
}

and then use %{VSL:VCL_Log:true_status}x in the varnishncsa format line to
retrieve it
-- 
Guillaume Quintard


On Thu, Oct 31, 2019 at 9:17 AM Rainer Canavan <
rainer.canavan+varnish at sevenval.com> wrote:

> Hi,
>
> we want to get a better understanding how well our varnish setup is
> performing. We've got two varnishncsa running, one with '-b' and one
> without, and each with their own logformat configuration. Each of
> those configurations contains "status":%s. Varnish version is
> varnish-6.2.1.
>
> If varnish successfully revalidates a stored response, i would expect
> the backend log to show a status of 304, and the client log a status
> of 200, but in reality, the vanishncsa running with "-b" also reports
> a status of 200.
>
> Just to make sure, I've watched with tcpdump what's going on, and
> varnish does really receive a 304 from the backend. The client sends
>
> GET /test/5db010a2-07a5-4119-b90b-ed7328c42231 HTTP/1.1
> Host: cachetest.backend
> [...]
>
> and receives from varnish:
>
> HTTP/1.1 200 OK
> Cache-Control: max-age=3600
> Date: Thu, 31 Oct 2019 14:43:19 GMT
> Etag: "ASKCUMEWOGYQIAS"
> [...]
>
> The same request between varnish and the backend:
>
> GET /test/5db010a2-07a5-4119-b90b-ed7328c42231 HTTP/1.1
> Host: cachetest.backend
> If-None-Match: "ASKCUMEWOGYQIAS"
> [...]
>
> HTTP/1.1 304 Not Modified
> Cache-Control: max-age=3600
> Date: Thu, 31 Oct 2019 14:43:19 GMT
> Etag: "ASKCUMEWOGYQIAS"
> Connection: close
>
> Is there another statement for the varnishncsa log format that shows
> the "real" backend HTTP status? Does this work as intended, or is this
> a bug?
>
> Rainer
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>
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