Load balancing is done at the authoritative DNS level.
Users of authoritative DNS are recursive DNS servers.
Users that connect to and generate traffic to your datacenters might share recursive DNS servers, and some recursive DNS servers serve more users than others.
Example Setup:
www.domain.com 1.2.3.4 (Weight 2)
www.domain.com 1.2.3.5 (Weight 2)
That means that 1.2.3.4 will be given to 2 out of 4 recursive DNS servers and that 1.2.3.5 will be given to 2 out of 4 recursive DNS servers.
That does not mean that traffic to 1.2.3.4 and 1.2.3.5 will be even as not all recursive DNS servers have the same number of end users.
So the traffic to your site may not match the weights you have set at the DNS level.
