FGCP HA active-active questions

Hi Forum,

I want to use two Fortigate 200E in an active-active cluster. I found some docs on how to setup the Cluster but I have a question left:

To get redundancy I need to patch each device with booth Fortigates, but the two Fortigates are acting as one unit. How is the redundancy realized? Via LinkAggregation?

Thank you!