Bill Woodcock wrote:
It may be that facebook uses all the four name server IP addresses in each edge node. But, it effectively kills essential redundancy of DNS to have two or more name servers (at separate locations) and the natural consequence is, as you can see, mass disaster.
Yep. I think we even had a NANOG talk on exactly that specific topic a long time ago.
https://www.pch.net/resources/Papers/dns-service-architecture/dns-service-ar...
Yes, having separate sets of anycast addresses by two or more pops should be fine. However, if CDN provider has their own transit backbone, which is, seemingly, not assumed by your slides, and retail ISPs are tightly connected to only one pop of the CDN provider, the CDN provider may be motivated to let users access only one pop killing essential redundancy of DNS, which should be overengineering, which is my concern of the paragraph quoted by you. Masataka Ohta