Traffic manager with app gateway uses the dynamic ip address which may change.

[traffic-manager-application-gateway-demo-setup](https://github.com/Azure/azure-quickstart-templates/tree/master/traffic-manager-application-gateway-demo-setup)

### Issue Details
In this template the traffic manager endpoints are set to the IP address of the Application gateway. However application gateway IP addresses are dynamic and therefore there is a chance these would change and cause the endpoint to fail.

To avoid that problem the traffic manager would need to use the DNS label for the app gateway public IP address and and set the endpoint to be an External endpoint to the and not an Azure Endpoint

Start by inspecting the traffic-manager-application-gateway-demo-setup template linked in the issue, especially its Traffic Manager and Application Gateway public IP configuration. Confirm how the endpoint target is currently selected and verify completion by ensuring it no longer depends on an address that may change.

Written by the indexing model from the issue text.