Comment by bushbaba
9 hours ago
Anycast can have serious reliability challenges. It was common at GCP for a small QPS user of anycast to have their Load Balancers nuked in a given pop as it was backed by a single machine. But BGP showed it as still the best route. The major DNS based offerings don't have such issues.
QUIC has support for preferred address, where anycast is used for the QUIC handshake then the connection migrates to a unicast address. It still has issues but it's nice to have sticky established connections and avoid flapping mid connection.
I work for a CDN that does DNS steering. DNS record lifetimes are nonzero and can be surprisingly long. But you do get some very fine control over where data goes if resolvers cooperate.