docs: update README and Ingress configuration for ok-server to clarify DNS usage

README.md

@@ -119,11 +119,19 @@ Expose the app with one of the two options below.
 
 k3s includes the Traefik ingress controller. The ClusterIP Service and Ingress
 in [k3s/expose-ingress.yaml](k3s/expose-ingress.yaml) expose the app on port 80
-of the node's IP address:
+for the host name `ok-server.example.org`. Change the `host` value in the
+Ingress to your own FQDN and point its DNS record at the node's IP address:
 
 ```bash
 kubectl apply -f k3s/expose-ingress.yaml
-curl -si "http://<node-ip>/"
+curl -si "http://ok-server.example.org/"
+```
+
+Without a DNS record you can still test the host rule by mapping the name to
+the node's IP address on the curl command line:
+
+```bash
+curl -si --resolve ok-server.example.org:80:<node-ip> "http://ok-server.example.org/"
 ```
 
 By default the app sees a cluster-internal address (for example `10.42.0.1`)