Added an example of fronting the playbook's integrated Traefik reverse-proxy with the existing Caddy container (not the apt-get or yum installed Caddy). Helpful for folks who have an existing server with a Caddy container already serving multiple applications.

examples/reverse-proxies/caddy2-in-container/Caddyfile

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+matrix.example.tld {
+
+  handle {
+        encode zstd gzip
+
+        # Use the docker service name instead of localhost or 127.0.0.1  here 
+        matrix-traefik:8080 {  
+               header_up X-Forwarded-Port {http.request.port}
+               header_up X-Forwarded-TlsProto {tls_protocol}
+               header_up X-Forwarded-TlsCipher {tls_cipher}
+               header_up X-Forwarded-HttpsProto {proto}
+        }
+  }
+}
+
+# Put `https://` at the beginning to enforce https protocol as 8448 is not the default https port (which is 443) 
+https://matrix.example.tld:8448 {
+    handle {
+        encode zstd gzip
+
+        #  Use the docker service name instead of localhost or 127.0.0.1  here 
+        reverse_proxy matrix-traefik:8448 {
+               header_up X-Forwarded-Port {http.request.port}
+               header_up X-Forwarded-TlsProto {tls_protocol}
+               header_up X-Forwarded-TlsCipher {tls_cipher}
+               header_up X-Forwarded-HttpsProto {proto}
+        }
+    }
+}
+
+
+example.tld {
+# Uncomment this if you are following "(Option 3): Setting up reverse-proxying of the well-known files from the base domain's server to the Matrix server" of https://github.com/spantaleev/matrix-docker-ansible-deploy/blob/master/docs/configuring-well-known.md#option-3-setting-up-reverse-proxying-of-the-well-known-files-from-the-base-domains-server-to-the-matrix-server
+    @wellknown {
+        path /.well-known/matrix/*
+    }
+
+    handle @wellknown {
+        reverse_proxy https://matrix.example.tld {
+            header_up Host {http.reverse_proxy.upstream.hostport}
+        }
+    }
+}

examples/reverse-proxies/caddy2-in-container/README.md

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+# Caddy reverse-proxy fronting the playbook's integrated Traefik reverse-proxy
+
+This directory contains a sample config that shows you how to front the integrated [Traefik](https://traefik.io/) reverse-proxy webserver with your own container-ed  [Caddy](https://caddyserver.com/) reverse-proxy. If you have a server with a Caddy container already serving several applications. And you want to install Matrix on it, but you don't want to break the existing traffic routing (so that the existing applications keep running smoothly). Then this guide is helpful.
+
+Ps. If you have a `apt-get ` or `yum` installed caddy instead of container-ed Caddy, please see [caddy2](../caddy2/README.md).
+
+
+## Prerequisite configuration
+
+To get started, first follow the [front the integrated reverse-proxy webserver with another reverse-proxy](../../../docs/configuring-playbook-own-webserver.md#fronting-the-integrated-reverse-proxy-webserver-with-another-reverse-proxy) instructions and update your playbook's configuration (`inventory/host_vars/matrix.<your-domain>/vars.yml`).
+
+And adjust the `docker-compose.yaml` of Caddy's. See [examples/reverse-proxies/caddy2-in-container/docker-compose.yaml](./docker-compose.yaml).
+
+
+## Using the Caddyfile
+
+You can either just use the [Caddyfile](Caddyfile) directly or append its content to your own Caddyfile.
+In both cases make sure to replace all the `example.tld` domains with your own domain.
+
+This example does not include additional services like element, but you should be able copy the first block and replace the matrix subdomain with the additional services subdomain. I have not tested this though.

examples/reverse-proxies/caddy2-in-container/docker-compose.yaml

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+version: "3.9"
+
+services:
+  caddy:
+    image: caddy:2.5.1-alpine
+    networks:
+      # add this, so that caddy can talk to the playbook-managed-traefik 
+      - traefik
+    ports:
+      - "80:80"
+      - "443:443"
+      - "8448:8448"
+    volumes:
+      - ./Caddyfile:/etc/caddy/Caddyfile
+    #   - ./site:/var/www
+    # Other configurations ...
+
+networks:
+  # add this as well
+  traefik:
+    name: traefik
+    external: true