Mysterious no content result, from an URL with pass action

[Guillaume Quintard]

On Tue, May 9, 2023, 22:45 Jakob Bohm <jb-varnish at wisemo.com> wrote:

> Expecting uncachable results that vary with time and are only sometimes
> 204,


Understood, but that one looks like a backend issue. Also, just to be
clear, the response is uncatchable because the back looked at the url and
deemed the request wouldn't lead to cacheable content, so we knew the
response would be uncatchable before even contacting the backend

and the response time is also somewhat unexpected, but is not
> clearly logged (only a Varnish expert like you can decrypt that it is 27
> seconds).


To be fair, varnishlog's goal is just to provide all the info it can, in an
unopinionated matter. The fact that the response took a long time may or
may not be normal, so there's no reason for varnishlog to fret about it,
and it doesn't necessarily know either what duration you are interested in,
so it gives them all)
For anyone reading along and trying to make sense of the Timestamp lines:
https://varnish-cache.org/docs/6.0/reference/vsl.html#timestamps

Note that varnisncsa would have probably been more concise and maybe useful
to check the timing.

It is also unclear if Varnish is always receiving those
> responses from the backend.
>

As a rule of thumb, by default, varnish only generates 503s in case of an
error (your VCL can also generate other errors, but then you are expected
to know about that).

A quick way to tag the transport-level error that varnish will generate on
the backend side it to have this in your VCL:

``` vcl
sub vcl_backend_error {
    set beresp.http.is-a-varnish-error = "true";
}

>
> I also expected some other URLs in the log, but don't see them.
>

You could maybe log more, on disk, and filter for the urls you care about?
If that's not what you are already doing?

This page might help: https://docs.varnish-software.com/tutorials/vsl-query/

Hope that helps!

>
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