Use the following procedure to upgrade a pair of firewalls in a high
availability (HA) configuration. This procedure applies to both
active/passive and active/active configurations.
To avoid downtime when upgrading firewalls that are in a high availability
(HA) configuration, update one HA peer at a time: For active/active
firewalls, it does not matter which peer you upgrade first (though for
simplicity, this procedure shows you how to upgrade the active-secondary
peer first). For active/passive firewalls, you must upgrade the passive peer
first, suspend the active peer (fail over), update the active peer, and then
return that peer to a functional state (fail back). To prevent failover
during the upgrade of the HA peers, you must make sure preemption is
disabled before proceeding with the upgrade. You only need to disable
preemption on one peer in the pair.
To avoid impacting traffic, plan to upgrade within the outage window.
Ensure the firewalls are connected to a reliable power source. A loss of
power during an upgrade can make firewalls unusable.