Selfhosted

Yes, it'd work just fine because each container listens on port 8000 of their own IP address, not the docker server's IP address. Caddy/Traefik just redirects traffic to that port.

Caddy would have the bridge proxy network and the port 443 exposed.

version: "3.7"

networks:
  proxy-network:
    external: true
# needs to be created manually bevor running (docker create network proxy-network)
services:
  caddy:
    image: caddy
    container_name: caddy
    restart: unless-stopped
    ports:
      - 80:80
      - 443:443
    volumes:
      - ./data:/data
      - ./config:/config
      - ./Caddyfile:/etc/caddy/Caddyfile:ro
    networks:
      - proxy-network

Other services:

version: "3.7"

networks:
  proxy-network:
    external: true

services:
  app:
    image: app
    container_name: app
    restart: unless-stopped
    volumes:
      - ./app-data:/data
    networks:
      - proxy-network

Caddy can now talk to the app with the apps container_name.

Caddyfile:

homepage.domain.de {
    reverse_proxy app:80
}

So the reverse proxy network is an extra network only for containers that need to be exposed.

so what you ideally want is people to ONLY be able to access your backend service through caddy, so caddy should be the only one with ports publicly accessible, yes

caddy running in the same docker network as your services can talk to those services on their original ports; they don’t need to even be mapped to the host! in this case, you have 3 containers: caddy, service 1, service 2… caddy is the only one that needs to have ports forwarded and you can just forward caddy:443 and no need to worry! then caddy can talk directly to services:80 or services:443 (docker containers show up to other docker containers by their container name! so if you run eg: docker run … —name lemmy, then caddy in the same docker network would be able to connect to http://lemmy:80!)

.. but if you forward say service 1 and 2 on :8443 and :9443 (without firewall, and even with it makes me uncomfortable - that’s 1 step away from a subtle security problem), someone could be able to access <yourserver>:8443, right? so they don’t have to go through caddy to get to the backend service… for some services, that can be a big deal in ways that it’s difficult to understand, so it’s best to just not allow it if possible

an alternative is to make sure your services are firewalled so that nobody from the internet can hit them, but caddy still can… but i like this less, because it’s less explicit what’s happening so it’s easier to forget about