Global Load Balancing: GeoDNS, Anycast BGP, & Latency Routing

Global Load Balancing (GLB) directs incoming user traffic to the geographically or topologically closest healthy cloud region:

How GeoDNS Works:

1. When a client performs a DNS query for api.example.com, the request reaches an authoritative nameserver (e.g., AWS Route 53, NS1, Cloudflare).
2. The nameserver inspects the client's IP address (or the EDNS Client Subnet - RFC 7871 passed by recursive resolvers) and looks up its location in a global GeoIP database (MaxMind / IP2Location).
3. The nameserver returns an A/AAAA record pointing to the datacenter with lowest network latency (e.g., us-east IP for New York users, eu-central IP for Berlin users).

Routing Policies in Modern DNS:

• Geolocation Routing: Routes users based on geographic boundary (country, state, continent).
• Latency-Based Routing: Uses continuous global network telemetry to route users to the AWS/GCP region providing lowest measured latency.
• Weighted Round-Robin / Canary Routing: Shifts percentages of traffic (e.g., 10\% to new region) during canary rollouts.