When processing a DNS query, Amazon Route 53 searches for a resource record set that matches the specified name and type. If a group of resource record sets have the same name and type, Amazon Route 53 selects one from that group. The probability of any one resource record set being selected depends on its weight as a proportion of the total weight for all resource record sets in the group:
For example, suppose you create three resource record sets for www.example.com. The three A records have weights of 1, 1, and 3 (sum = 5). On average, Amazon Route 53 selects each of the first two resource record sets one-fifth of the time, and returns the third resource record set three-fifths of the time.