Thank you for getting back and sharing additional details.
I concern how to communicate the public ip from the on-prem server to application gateway and WAF without the need of using any vpn between azure and our on-prem server
Yes, as the on-prem servers have Public IP addresses there is no need to create a VPN connection and you should be able to add them as backend to the Application Gateway.
The requirements for the backend pool members for Azure Application Gateway are currently documented here. An application gateway can communicate with instances outside of the virtual network that it's in. As a result, the members of the backend pools can be across clusters, across datacenters, or outside Azure, as long as there's IP connectivity.
About the second image, I'm not quit sure if it's possible the desing showed.
In Azure Application Gateway a listener is a logical entity that checks for connection requests. It's configured with a frontend IP address, protocol, and port number for connections from clients to the application gateway. So, you can have only one HTTPS basic listener (port 443). This documentation explains how Azure Application Gateway Works.
Depending on how wish to set-up access to your web application you can choose between basic and multi-site listeners.
If you want all of your requests (for any domain) to be accepted and forwarded to backend pools, choose basic. Learn how to create an application gateway with a basic listener.
If you want to forward requests to different backend pools based on the host header or host names, choose multi-site listener. Application Gateway relies on HTTP 1.1 host headers to host more than one website on the same public IP address and port. To differentiate requests on the same port, you must specify a host name that matches with the incoming request. To learn more, see hosting multiple sites using Application Gateway.
Hope this helps! Please let me know if you have any questions. Thank you!
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