I am establishing a site to site vpn from on prem to Azure, however, i cannot assign a static public ip to it. Per this link, https://docs.microsoft.com/en-us/azure/virtual-network/virtual-network-ip-addresses-overview-arm, it's designed that way. Can someone please explain why and what if the dynamic ip changes on azure end? Then the site-site vpn breaks. Unless Azure assumes the tunnel is always running, it will keep that dynamic IP.
VPN gateways An Azure VPN Gateway connects an Azure virtual network to other Azure virtual networks, or to an on-premises network. A public IP address is assigned to the VPN Gateway to enable it to communicate with the remote network. You can only assign a dynamic basic public IP address to a VPN gateway.