What is the first step in upgrading the firmware for an HA cluster?

Logging into the GUI of the primary device is the correct first step in upgrading the firmware for a High Availability (HA) cluster. This is because the primary device typically manages the configurations and the firmware upgrade process in an HA setup. When you access the GUI of the primary device, you can efficiently initiate the upgrade for the entire cluster while ensuring that the HA functionality remains intact.

When upgrading firmware in an HA cluster, the primary unit usually coordinates the process to minimize downtime and ensure that the secondary device can take over if the primary encounters issues during the upgrade. This centralized approach through the primary device's interface supports the synchronized management required in HA configurations.

The other options, while relevant in the context of managing devices, do not set the appropriate groundwork for starting the upgrade process. Logging into the CLI of the secondary device would not be advisable as the primary device is responsible for initiating upgrades. Upgrading the secondary device first could lead to inconsistencies or potential lapses in service. Checking the HA status, although important during maintenance routines, is not specifically the step that initiates the firmware upgrade process.