Here a very quick tip, when you deploy a WebApp pattern you can see next to the WAS role the URL (Endpoint) to access your deployed app:
This can be easily achieved and just by adding a line in your topology template.
1) Locate the role in the roles array for which you would like to add the link.
2) Insert a line like:
"external-uri": [{"ENDPOINT":"http://{SERVER}:8080/${attributes.appURL}"}],
Now, the question is where the {SERVER} comes from?
When we look at the storehouse, we can see that the {SERVER} is still present in the generated topology and thus I have the feeling that this variable is interpreted by the UI as being the IP address of the server where the WAS role has been deployed.
In fact you can insert any parameters defined in the tweak.json between braces and they will be replaced by their value.