503 (Service Unavailable) from Varnish on POST request using Digest Authentication

Guillaume Quintard guillaume at varnish-software.com
Mon May 14 09:54:39 UTC 2018

Duh, right, I got really confused with the old log format. Sorry for the

Guillaume Quintard

On Mon, May 14, 2018 at 11:50 AM, Sergio Rus <sergio at sergiorus.com> wrote:

> Well, this issue is not really about the authentication process itself. As
> I said, the endpoint was using Digest Authentication, but I was
> intentionally not including the auth header, so I was expecting to get in
> the client a 401 UNAUTHORIZED response, but instead I was getting a 503
> coming from Varnish. Everything works fine without Varnish: the client gets
> the 401 UNAUTHORIZED in every case, using any payload size. So I just
> wanted to understand why Varnish was failing with a 503, and after several
> tests I found that reducing the payload size a little bit, keeping it
> around 7K-8K, it worked. A few bytes bigger, close to 8K, it failed (503).
> To me, it looks like Varnish has some sort of size limit for the objects
> that can keep in memory that is not only applied for the headers size, but
> also for the payload in POST requests. Unfortunately I couldn't find in the
> documentation any parameter related to this. But as I said, increasing a
> parameter wouldn't be the right solution, because at some point it would
> fail again with bigger payloads.
> Cheers
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