This Nominated Discussion Article is based on the post "Adding a firewall back into a AP cluster that has outdated network and device settings" by @AlanDeBoer and responded to by @Raido_Rattameister. Read on to see the solution!
I'm curious if anyone can provide an article or just some basic steps of adding a firewall back into a AP cluster that has "outdated" network and device settings.
Firewall-02 was moved to a new location and has a new IP scheme for the network and device settings.
Firewall-01 will be physically moved and needs to rejoin the cluster, but it does have outdated IP settings.
I'm assuming the first step is to power up 01 without any copper/fiber connected and console into 01 and update the device management IP first.
Step 1 - Take config backup from both firewalls (Device > Setup > Operations).
Step 2 - Make sure that "Device Priority" of Firewall-02 is lower than Firewall-01 to make sure Firewall-02 stays active firewall.
Step 3 - Cabling (at minimum HA1 cable).
Step 4 - Click "Sync to peer" in Firewall-02 (Dashboard > High Availability widget).
If you click "Sync to peer" on Firewall-01 you will push old nic scheme from Firewall-01 to Firewall-02 and your network will go down!
In addition, mgmt IP change as you pointed out.