Connection issues with Varnish

[Martynas Jusevičius]

Hi,

I have code making a lot of PUT and POST requests to Varnish.
I have noticed that quite a few of those fail due to a closed
connection, and Apache HTTP Client hangs for a while (10-30s,
sometimes more) around the same time.

If I remove Varnish from the setup and write directly to the backend,
the errors go away completely. So I'm confident the issue is
Varnish-specific.

The VCL is rather trivial and I don't think it's the core of the
problem, but I cannot be sure. It can be found here:
https://github.com/AtomGraph/LinkedDataHub/blob/develop/platform/varnish.vcl.template

How would I go about debugging this? What should I look for in the
logs? Your help is much appreciated.

Best,

Martynas