In AWS, for Route 53, when you choose the [...] routing policy for your DNS records (i.e. you specifiy multpile A records with the same Name/Type but different values, e.g. different IPs), Route 53 will return the value to the user based on the number you assigned to the record (e.g. if you assign 20 to first record, 30 to second, and 50 to third, then user gets the value of first records 20% of the time).

Weighted

^^ note the weights are numbers that get added up and then distributed accordingly (e.g. 20 to first 30 to second, 50 to third, adds up to 100, so first record will get 20/100, i.e. 20% of the traffic.