Role of a controller in an instance. The
default role of a controller is equal. In this
role, the controller has full access to the
switch and is equal to other controllers in
the same role. In slave role, the controller
has read-only access to the switch. The
master role is similar to equal and has full
access to the switch, the difference is that
the switch ensures it is the only controller
in this role. When a controller changes its
role to master, the switch changes all other
controllers with the role master to have the
role slave.