feat(traefik): configurable extra_hosts for container DNS overrides

Add `traefik_extra_hosts` (list of `host:ip`) that maps straight into
the traefik container's compose `extra_hosts`. Needed when a downstream
middleware (e.g. ForwardAuth to authentik on a sibling LAN) has to
resolve a public FQDN to an internal IP because the DMZ doesn't hairpin
the public address back inside.

Empty by default; behaviour unchanged for existing inventories.

roles/traefik/defaults/main.yml

@@ -11,6 +11,13 @@ service_name: traefik
 docker_compose_dir: "{{ docker_compose_base_dir }}/{{ service_name }}"
 docker_volume_dir: "{{ docker_volume_base_dir }}/{{ service_name }}"
 
+# Optional /etc/hosts entries injected into the traefik container. Useful
+# when downstream middlewares (e.g. ForwardAuth to an authentik instance
+# running on a sibling LAN) need a public FQDN to resolve to an internal
+# IP because the DMZ doesn't hairpin the public address back inside.
+# Example: ["auth.example.com:172.16.19.101"]
+traefik_extra_hosts: []
+
 # Deployment mode: 'dmz' or 'backend'
 # - dmz: Public-facing reverse proxy that routes to backend servers using file provider
 # - backend: Application server with docker provider for local container discovery

roles/traefik/templates/docker-compose.yml.j2

@@ -33,6 +33,12 @@ services:
 {% endif %}
     networks:
       - {{ traefik_network }}
+{% if traefik_extra_hosts | default([]) | length > 0 %}
+    extra_hosts:
+{%   for h in traefik_extra_hosts %}
+      - "{{ h }}"
+{%   endfor %}
+{% endif %}
 
 networks:
   {{ traefik_network }}: