How are load balancers used in modern application deployments?

How are load balancers used in modern application deployments?

A. Turn off traffic and take down compute units, then update and bring the compute units back up. B. Allow traffic to continue as new compute units are brought up and old compute units are taken down. C. Allow HTTP and HTTPS traffic to continue as old compute units are discontinued before new units are brought up. D. Bring up new compute units, test the compute units, and switch the traffic from old units to new units.