Based on the provided exhibit showing an active-passive FortiGate High Availability (HA) pair with external and internal Azure load balancers and without the use of an SDN connector, the administrator should implement a Probe IP address with two static routes (Option B).
* Probe IP Address:Azure load balancers use a health probe to determine the health of the instances in the backend pool. The health probe ensures that the load balancer only directs traffic to the active (primary) FortiGate in an HA pair.
* Two Static Routes:Given that this is an active-passive setup, static routing should be used to ensure deterministic traffic flow. Two static routes would be configured to ensure that traffic can flow to the active unit and be correctly routed to the protected subnets in failover scenarios.
References:The recommendation for using a Probe IP address with static routes is based on Azure's best practices for load balancer configuration, particularly for HA scenarios, as well as on Fortinet's HA documentation for clouddeployments. This setup ensures high availability while allowing proper traffic distribution based on the health probe's findings.

Explanation
According to the AWS documentation for Transit Gateway, a Transit Gateway is a network transit hub that connects VPCs and on-premises networks. To route traffic from Linux instances to the TGW, you need to do the following steps:
In the TGW route table, associate two attachments. An attachment is a resource that connects a VPC or VPN to a Transit Gateway. By associating the attachments to the TGW route table, you enable the TGW to route traffic between the VPCs and the VPN.
In the main subnet routing table in VPC A and B, add a new route with destination 0_0.0.0/0, next hop TGW. This route directs all traffic from the Linux instances to the TGW, which can then forward it to the appropriate destination based on the TGW route table.
The other options are incorrect because:
In the TGW route table, adding route propagation to 192.168.0 0/16 is not necessary, as this is already the default route for the TGW. Route propagation allows you to automatically propagate routes from your VPC or VPN to your TGW route table.
In the main subnet routing table in VPC A and B, adding a new route with destination 0_0.0.0/0, next hop Internet gateway (IGW) is not correct, as this would bypass the TGW and send all traffic directly to the internet. An IGW is a VPC component that enables communication between instances in your VPC and the internet.
[Transit Gateways - Amazon Virtual Private Cloud]

* Transit Gateway Connect Specificity: AWS Transit Gateway Connect is a specific feature designed to streamline the integration of SD-WAN appliances and third-party virtual appliances into your Transit Gateway.expand_more It utilizes a specialized attachment type.exclamation
* BGP's Role: While Transit Gateway Connect attachments leverage BGP for dynamic routing, BGP itself is a routing protocol and not the core connectivity mechanism in this context.
* GRE Tunneling: GRE is a tunneling protocol commonly used with Transit Gateway Connect attachments to encapsulate traffic.

The variables.tf file shows that the FortiGate VM will be deployed in the eu-West-Ia region with private and public subnets. The region variable is set to "eu-west-1" and the availability_zone variable is set to "eu-west-1a". The vpc_id variable is set to "vpc-0e9d6a6f" and the subnets variable is set to a list of two subnet IDs: "subnet-0f9d6a6f" and "subnet-1f9d6a6f". The license_type variable is set to "on-demand" and the ami_id variable is set to "ami-0e9d6a6f".

A VPC attachment is the type of attachment that allows you to connect a VPC to a TGW and advertise routes through BGP. A VPC attachment creates a VPN connection between the VPC and the TGW, and enables dynamic routing with BGP. A connect attachment is used to connect a VPN or Direct Connect gateway to a TGW. A route attachment is not a valid type of attachment for TGW. A GRE attachment is used to connect a FortiGate device to a TGW using GRE tunnels. References:
* Creating the TGW and related resources
* Configuring TGW route tables
* FortiGate Public Cloud 7.2.0 - Fortinet Documentation
* Updating the route table and adding an IAM policy