Load Balancing Method to use

Can anyone suggest what LB method i can use with this scenario:

Server A: 1.1.1.1

Sever B: 1.1.1.2

We want the traffic ONLY goes to 1.1.1.1 unless it is down/offline, the traffic will go to 1.1.1.2

Is there a LB method we can use? If yes, what is it?

Or we need an iRule for this?