Redundant Datacenter Setup

Hello everyone!

As part of our network infrastructure, we currently have a HEADQUARTER "A," which houses a datacenter with servers and services accessed from all our LANs (both in branch offices and headquarters).

We are considering establishing a second HEADQUARTER ("B"), which will contain a mirrored datacenter to that of HQ "A."

Considerations:
Both HQs have Fortigate edge firewalls:

HQ "A": Fortigate 600E
HQ "B": Fortigate 900G
Both HQs and BOs are connected to a common MPLS service and have internet access through one or more ISPs.

There is a dedicated fiber optic connection currently in use between HQ "A" and HQ "B."

The objective is to ensure that, if the datacenter at HQ "A" becomes unavailable due to a technical issue (e.g., failure of HQ "A"'s firewall), the rest of the LANs can continue consuming services through HQ "B" until HQ "A"’s firewall is restored and resumes its primary role.

Therefore, we would like to ask for your guidance on which Fortigate features and functions we can utilize to implement the technical requirements described above.

I am attaching a network diagram for a better understanding of the current infrastructure.

Best regards.