This procedure explains how to configure two Fortigate firewalls in clustered mode, for high availability. Both firewalls need to have the same firmware version. In my case they both have a version 3, With a built 400. I've set up the following features for each of them:

If we want to configure the firewall for when an internet connection goes down, it automatically goes out with another and the users “almost” do not realize it you have to follow the steps of this procedure. It is applicable to any Fortigate, Logically, what you have to have is two connections from different suppliers in the organization, for example, we can have Timofonica on the WAN1 and Güanadú on the WAN2, in case the Timofonica connection drops (something quite frequent) that the connection we have with Güanadú be lifted.