Added config sample for synapse admin with traefik 2

docs/configuring-playbook-synapse-admin.md

@@ -32,3 +32,31 @@ After installation, Synapse Admin will be accessible at: `https://matrix.DOMAIN/
 To use Synapse Admin, you need to have [registered at least one administrator account](registering-users.md) on your server.
 
 The Homeserver URL to use on Synapse Admin's login page is: `https://matrix.DOMAIN`
+
+### Sample configuration for running behind Traefik 2.0
+
+Below is a sample configuration for using this playbook with a [Traefik](https://traefik.io/) 2.0 reverse proxy.
+
+This an extension to Traefik config sample in [own-webserver-documentation](./configuring-playbook-own-webserver.md).
+
+```yaml
+# Don't bind any HTTP or federation port to the host
+# (Traefik will proxy directly into the containers)
+matrix_synapse_admin_container_http_host_bind_port: ""
+
+matrix_synapse_admin_container_extra_arguments:
+    # May be unnecessary depending on Traefik config, but can't hurt
+    - '--label "traefik.enable=true"'
+
+    # The Synapse Admin container will only receive traffic from this subdomain and path
+    - '--label "traefik.http.routers.matrix-synapse-admin.rule=(Host(`{{ matrix_server_fqn_matrix }}`) && Path(`{{matrix_synapse_admin_public_endpoint}}`))"'
+
+    # (Define your entrypoint)
+    - '--label "traefik.http.routers.matrix-synapse-admin.entrypoints=web-secure"'
+
+    # (The 'default' certificate resolver must be defined in Traefik config)
+    - '--label "traefik.http.routers.matrix-synapse-admin.tls.certResolver=default"'
+
+    # The Synapse Admin container uses port 80 by default
+    - '--label "traefik.http.services.matrix-synapse-admin.loadbalancer.server.port=80"'
+```