High Avaibility

Hello In the coming days I will set up a freeradius server for access control and accounting. I've been looking for information on freeradius and high availability, since my idea is to have two servers in case one fails, continue to operate with the other, but I just found information. So I turn to the list, in case I can recommend someone with experience on stage. I do not know if it is feasible to have a server as master and one slave, when the main falls, the other up the interface. If there is some kind of balancer radius and use both servers, etc.. Any ideas?. Thank you very much. Best regards Anto