Why do I see this error in a well functioning backup?

I have been testing and trying with Duplicati for the last couple of weeks. Especially debugging communication setups took some time until I had everything working.

Now, on my test machine I have only one test backup set still active and it backs up to my minio server, which is behind an nginx handling the TLS termination.

But nginx still logs an error like this every time my test backup set runs:
2017/12/31 16:18:35 [error] 33846#0: *1 kevent() reported that connect() failed (61: Connection refused) while connecting to upstream, client:, server: MYNGINXMINIOSERVER, request: “GET /gerbentest2?max-keys=1000 HTTP/1.1”, upstream: “http://[::1]:9003/gerbentest2?max-keys=1000”, host: “MYNGINXMINIOSERVER:9000”

Duplicati does not mention an error in its logs (as far as I can see). But somehow Duplicati triggers a connect error when trying to reach my minio server. Is Duplicati trying multiple times or in multiple ways, recovering form this error? How do I find out?

I believe duplicati tries 5 times. Don’t think you will see the failed attempts as errors or warnings unless you enable logging.

I have enabled logging this way on the server: “–log-file=/Library/Logs/duplicati_server.log --log-level=Information --verbose=true”. I would expect any error to show up in duplicatie_server.log or on stderr. Stderr remains mute, and stdout only shows a “No certificates found” message.