Caddy in docker blocked accessing other docker containers

[Whitestrake (Matthew Fay)]

@audas

There is even a WIKI how to do exactly what I am asking from one of the authors of Caddy Matt Holt describing precisely what I am attempting to do.

Are you referring to this part?

@matt

Once Caddy is running as a service, you can change the config file to be a reverse proxy. There is no 1 config that works for everyone, so please, customize this as necessary:

example.com

reverse_proxy /service-a/* 192.168.0.2:8001
reverse_proxy /service-b/* 192.168.0.2:8002

There’s one major difference, actually. A huge difference.

That example config isn’t stripping the URI prefix, whereas handle_path does. That means for both upstreams, the request includes the /service-X/ prefix. In turn that means, by necessity, both upstreams must have been configured to expect that prefix and respond appropriately.

To be absolutely unambiguous here, with Matt’s example, you make a request to example.com/service-a/foo and Caddy proxies that request to 192.168.0.2:8001/service-a/foo. With YOUR config, you’re trying to make a request to 144.6.86.11/homarr/foo and have Caddy proxy to homarr:7575/foo. Did you note the missing /homarr prefix? You’ve configured Caddy to hide that part from the upstream app, so it has no idea it’s there. The app only sees Caddy asking for /foo.

As I’ve explained, the subfolder problem arises when you try to “trick” an upstream app to put it in a subfolder and that upstream app isn’t properly configured to do so. It’s a logic disagreement between the web server and the upstream app.

@audas

Just trying to wrap my head around why we are meant to use sub domains now and not paths - and why paths wont work etc

How has this changed ?

There is no inconsistency here, and our advice has never changed, only your understanding of it.

Caddy documentation even references the wiki post regarding the subfolder problem.

A full Caddyfile example, where handle_path and handle are mutually exclusive; but, be aware of the subfolder problem

—handle_path (Caddyfile directive) — Caddy Documentation

@audas

Is there an alternative system that I could approach this with?

I wish I could make a recommendation, but to the honest, absolute best of my knowledge, I am not aware of ANY software which can automatically resolve subfolder-related proxy/upstream conflicts.

The closest I can think of is that Apache httpd has a ProxyPassReverse directive which fixes specifically Location headers somewhat automatically. Caddy has no specific syntactic sugar to make this happen, but it can be done with a header_down rewrite.

ProxyPassReverse very explicitly does not fix URLs in assets specified in HTML as it is not a HTML filter. That is what the custom module caddyserver/replace-response is for in our case, and I’m not sure what the equivalent is in Apache but I’m quite HTML filtering is doable in their ecosystem - I just haven’t had to go there, myself.

Paths absolutely can work. I personally have quite a few apps in my mediaserver stack running in subfolders: Tautulli, Sonarr, Radarr, Lidarr, NZBHydra 2, NZBGet, and TubeSync.

I have a few others in that stack that I have not been able/felt it necessary to configure to play nicely in a subfolder, though: Maintainerr, Heimdall, Plex, CloudTorrent, and Overseerr.