Load Balancer help

Hello,

i hope you are doing well, i have ordered for our customer Load Balancing services for domain name, since we have setup two servers, ServerA is the master and ServerB is cluster in order that ServerA has issues, the traffic should be transferred to ServerB.
In cloudflare is really too complicated to do it by myself, would you please help me to setup this.
So, load balancer will have two origin servers ServerA as a Master and ServerB as a cluster, in order that ServerA will have issues/downtime the traffic to be transferred to ServerB?

Looking forward to hearing from you.
Cheers.