Pitfalls.. Well - knowing the steps in detail helps, but can't really avoid some downtime.
First prepare your Standby controller with all necessary config (basically just IP/network) and correct AOS.
Activate Centralized Licensing on the Master..
If you re-use the current master IP as VIP
* Change Master IP to new IP1, reboot
* Add VRRP on Master, verify that the VIP is up and running again in VRRP Master state
-> At this time the AP's will start connecting to Master again.
* Add VRRP on Standby, verify that it has VRRP Backup state
* Add Master Redundancy settings on Master
* Add Master Redundancy settings on Standby
* Verify that database is in sync, or force a database sync. Verify that all settings/config are on the Standby
Or - use a new IP as VRRP and prepare everything as mentioned above. When you're ready to do the switch change your DNS entry for aruba-master (or dhcp options) towards the new VIP. At this time all the AP's will reboot, and connect to the new VIP. Some delay in updating DNS might occur..
And if you're using RAP's just make sure you update DNS and/or NAT ip's ..