No matter how meticulously you design a failover, what actually sends users to the new region in the last kilometer is, in the end, DNS. That single query where a user's browser turns api.example.com into an IP decides which region and which instance the traffic flows to. Route 53 became a "global traffic control plane" beyond a simple name-to-IP translator because it lets you change DNS answers dynamically based on location, latency, weight, and health. This article follows the working principles of DNS, Route 53's 7 routing policies, the internal behavior of Health Checks, and how Alias, Private Hosted Zone, and DNSSEC underpin safe and flexible routing.
First we must pin down the essence of DNS