ELB (Elastic Load Balancer) in two LNS's in multiple AZ?


How to use ELB (Elastic Load Balancer) in two LNS’s (i.e. one instance is created for LNS and the latter is the replica of the former instance, how can we assign same IP to both) in multiple AZ, connecting to single APP server? I have also used AWS environment, now i need HA (High Availability) environment so it would be great if someone can give me the solution for the same.