GeoDNS vs anycast for failover
GeoDNS picks an edge by name lookup, and resolvers keep the old answer until the TTL ends. Anycast uses one address and withdraws the route of a failed edge. When edge A stops at 0:10, GeoDNS with a 60 s TTL gives 62.5 percent availability. Anycast stays above 97 percent.
GeoDNS, 60 s TTL · edge A stops at 0:10 · availability 62.5%
Anycast · edge A stops at 0:10 · availability 100%
Case 1
A global API serves 500 requests/s from two edges. Edge A stops at 0:10. Availability must stay above 97 percent and p99 below 300 ms.
| Measure | Goal | GeoDNS with a 60 s TTL | Anycast with route withdrawal |
|---|---|---|---|
| Availability | at least 97% | 62.5% Fail | 100% Pass |
| p99 latency | under 300 ms | 68 ms Pass | 68 ms Pass |
| Monthly cost | 12 USD/mo | 12 USD/mo | |
| Error rate | 37.5% | 0% |