| FortiGate-7000 devices support High availability in Active-Passive mode with only two devices.
Depending on the HA configuration, changing the priority or resetting the HA uptime triggers a failover.
To check the current HA configuration through CLI: config global
show full-configuration system ha
Priority, override, and monitor are the important elements to look at.
During the primary unit election in the 7000 cluster, if override is disabled, the following criteria are considered:
Override Disabled: Any Active FPMs -> Number of active FIM -> Connected Monitored Ports -> Number of Active FPMs -> HA uptime -> Priority -> Serial Number.
While the number of connected monitor ports, and Active FPMs / FIMs are identical, it is the HA uptime that acts as a tiebreak.
To force a failover, it is necessary to reset the ha uptime on the current primary: config global
diag sys ha reset-uptime If override is enabled the following criteria are considered:
Override Enabled: Any Active FPMs -> Number of active FIM -> Connected Monitored Ports -> Number of Active FPMs -> Priority -> HA uptime -> Serial Number.
To force a failover, it is necessary to change the priority:
config global
config system ha
set priority <priority number>
The unit with the highest priority will become primary.
Related article:
Technical Tip: Understanding the HA uptime for Chassis based device | 
