Geo-DNS and global load balancing
If your users are spread across the world, sending them all to one place adds latency for most of them. Geo-DNS answers the same name with a different address depending on where the question comes from.
Geo-DNS returns a different answer to the same query based on the asker’s location — a visitor in Europe gets your Amsterdam server, one in Asia gets a server closer to them. It is the simplest way to shrink latency for a geographically spread audience.
How it decides
The authoritative server looks at where the query appears to come from and picks the matching record set. Pair it with health checks so that if the nearest server is down, users are sent to the next-best one instead of a dead address — routing people efficiently to something broken is worse than useless.
The resolver-location catch
Geo-DNS sees the resolver’s location, not the user’s. Most of the time they are close, but a user on a distant public resolver can be sent to the wrong region. The EDNS Client Subnet extension helps by passing a hint of the real client network — worth enabling where accuracy matters.
Caching blurs the edges
DNS answers are cached along the way, so a change or a failover takes effect only as fast as your TTL allows. Keep TTLs low on geo-balanced records so a failover is quick — but not so low that you hammer the authoritative servers. See choosing DNS TTLs.
Geo-DNS or Anycast
Geo-DNS steers at the DNS layer and is simple to run. Anycast steers at the routing layer, announcing the same IP from several places, and reacts faster to failure — but needs BGP and address space. Many setups use both: Anycast for the DNS itself, Geo-DNS for the services behind it.
It is latency, not redundancy
Geo-DNS reduces distance; it is not by itself high availability. For that you still need healthy servers in each location and a plan for losing one — see high availability, honestly and spreading across locations.
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