FreePBX HA-Removing a Machine to add a new One.
If you would like to remove a node from your cluster and add a new one, please follow these steps:
Power off the machine you want to remove from the cluster. (No preparations are needed.)
Using the Cluster's IP address, click on the High Availability module under Settings.
Going to the Status page will show that freepbx-a (or -b) is the current active Master and freepbx-b (or -a) is offline.
Now follow the steps on joining a Node to your cluster here. If your old slave is still powered on when you try to join a new slave, it will error out, so make sure you power down the old slave.