Geolocation Routing: The DNS service maps the client's IP address to a geographical location. Based on the client's geographical location, the DNS service responds with the IP address of the server or load balancer that's closest or most appropriate for the client. This ensures that clients are generally directed to the server that's geographically closest to them, reducing latency.
Anycast Routing: In Anycast routing, multiple servers or load balancers share the same public IP address, and network routers direct client requests to the instance that's closest in terms of routing cost. This is a common approach used by global Content Delivery Networks (CDNs).
Latency-based Routing: The DNS service periodically checks the latency between various servers/load balancers and various IP addresses around the world. When a client makes a request, the DNS service estimates the latency to different servers based on the client's IP address and responds with the address of the server that's likely to provide the lowest latency.
Global Load Balancers: Cloud providers like AWS, Google Cloud, and Azure provide global load balancers that automatically route users to the nearest or best performing endpoint in a multi-regional deployment. For instance, AWS Route 53 works with Elastic Load Balancer (ELB) to direct traffic to the nearest load balancer.
🤔 Note that "nearest" may not always mean "geographically nearest". Depending on network conditions and the routing protocol's cost calculation, the "nearest" server could be one that's further away geographically but has a more efficient or less congested route.