Rancher base-url?

Hi, I was wondering if there is way to change the base-url for rancher 2.0 from / to something like “/rancher” ?

I want to run it behind a proxy and would prefer rancher to path to me www.something.com/rancher/ instead of www.something.com/

No; sharing multiple unrelated applications on the same subdomain is a bad idea for security and (mostly theoretical, but it happens) compatibility.

The UI is also entirely static files and has no mechanism to get what that path is supposed to be (without already knowing it, to make an API call).

Use a separate subdomain. They and letsencrypt certs are free.