V2: reverse proxy but upstream server redirects to nonexistent path

[Whitestrake (Matthew Fay)]

One of these days I will make this post a wiki post:

Proxy URL not loading site?

Hi @robertgranholm, welcome to the Caddy community. We all started somewhere! In this case, you’ve run straight into one of the most prevalent obstacles people face when trying to reverse proxy apps - the “subfolder problem”. You’ll hit this regardless of what program you use as a reverse proxy, because it’s a logical problem, not a bug in the web server or the app itself. Just about every app is written under the assumption that it is being served at the web root, i.e. example.com/ - but in y…