You can configure web caching on a FortiGate HA cluster. The recommended best practice HA configuration for web caching is active-passive mode. When the cluster is operating, all web caching sessions are processed by the primary unit only. Even if the cluster is operating in active-active mode, HA does not load-balance web caching sessions.

In a cluster, only the primary unit stores the web cache database. The databases is not synchronized to the subordinate units. So, after a failover, the new primary unit must build its web cache.