How CDNs, anycast, load balancing, and migrations use DNS in production, and how to monitor it across many domains.
Why a lookup shows the CDN, not the origin
Visitor
looks up the domain
CDN edge
104.21.x.x
this is what DNS returns
Origin server
real IP, never exposed
A content delivery network's real magic happens at the DNS layer, before a single byte of content is ever requested.