Fabrikam requires encryption of VM-to-VM traffic between two VNets (VNet-EASTUS and VNet-WESTEU) in different regions. The VNets are currently peered. The security requirement is that traffic must be encrypted in transit without modifying the application. What is the most straightforward Azure solution and its prerequisites to meet this requirement?

The correct solution is to deploy Azure VPN Gateways in each VNet and configure a VNet-to-VNet IPsec/IKE VPN connection. This is the standard Azure method for encrypting traffic between VNets, especially across regions, without application modification. IPsec provides the required encryption in transit. Prerequisites include a gateway subnet in each VNet, public IPs for the VPN gateways, and a compatible VPN Gateway SKU. VNet peering itself does not encrypt traffic; it provides a direct, private connection. The 'Use remote gateways' option allows one VNet to use the other's gateway for on-premises connectivity but doesn't encrypt VNet-to-VNet traffic within the peering. NSGs filter traffic but do not encrypt it. Application Gateways provide application-layer (Layer 7) encryption (TLS) but require application modification or specific configurations to force all VM-to-VM traffic through them, which is not straightforward for general VM-to-VM communication.