Hi, All cluster units must bethe same FortiGate model with the same FortiOS firmware build installed. All cluster units must also have the same hardware configuration (for example, the same number of hard disks and so on) and be running in the same operating mode (NAT mode or transparent mode). I hope this helps to answer your query.
FortiGate-VM HA supports having two VMs in an HA cluster on the same physical platform or different platforms. The primary consideration is that all interfaces involved can communicate efficiently over TCP/IP connection sessions.
The Fortinet Security Fabric brings together the concepts of convergence and consolidation to provide comprehensive cybersecurity protection for all users, devices, and applications and across all network edges.