To implement security for the traffic between two VPCs in AWS, while keeping separate management of each department's VPC, two possible actions are:
Create a transit VPC with a FortiGate HA cluster, connect to the other two using VPC peering, and use routing tables to force traffic through the FortiGate cluster. This option allows the cybersecurity department to manage the transit VPC and apply security policies on the FortiGate cluster, while the other departments can manage their own VPCs and instances. The VPC peering connections enable direct communication between the VPCs without using public IPs or gateways. The routing tables can be configured to direct all inter-VPC traffic to the transit VPC.
Create a VPC with a FortiGate auto-scaling group with a Transit Gateway attached to the three VPCs to force routing through the FortiGate cluster. This option also allows the cybersecurity department to manage the security VPC and apply security policies on the FortiGate cluster, while the other departments can manage their own VPCs and instances. The Transit Gateway acts as a network hub that connects multiple VPCs and on-premises networks. The routing tables can be configured to direct all inter-VPC traffic to the security VPC. Reference: https://docs.fortinet.com/document/fortigate-public-cloud/7.2.0/aws-administration-guide/506140/connecting-a-local-fortigate-to-an-aws-vpc-vpn https://docs.fortinet.com/document/fortigate-public-cloud/7.0.0/sd-wan-architecture-for-enterprise/166334/sd-wan-configuration