Just to be unambigious, “it” here is the upstream app itself; Smokeping is issuing the redirect, and Caddy faithfully returns it to the downstream client.
As for why, it’s fairly simple; Smokeping appears to generate Location headers contextually aware of the
Host header the client used to access the site.
Smokeping sees a request for
Host: 192.168.1.4, which is true for Caddy, but not relevant for the actual client downstream - the client wants
You can pass through the
Host header, along with a few other useful headers for backend apps to get actual client-relevant information, with the
transparent preset for the