Beyond Round-Robin
Basic DNS returns a static list of IPs. GeoDNS adds location awareness, serving Berlin users the Frankfurt server and São Paulo users the Miami server—cutting latency and improving SEO Core Web Vitals.
How GeoDNS Works
Authoritative server inspects resolver’s IP (EDNS Client Subnet if present) against GeoIP database, then chooses closest healthy endpoint. Accuracy is country-level for free providers, city-level for premium.
Implementation Options
- Cloudflare Load Balancer: GUI, health checks, failover, $5/mo per origin
- AWS Route 53 Latency Policy: automatic AWS region mapping
- NS1 Filter Chain: Lua scripts for custom steering logic
- PowerDNS + GeoIP backend: self-hosted, unlimited flexibility
Health Checks & Failover
Monitor each origin via HTTP GET every 30 seconds. On failure, DNS automatically removes bad IP from pool (TTL 30 s). When health returns, IP re-enters rotation without human intervention.
Weighted Load Balancing
Send 70% traffic to primary VM, 30% to secondary for capacity testing. Adjust weights via API during flash sales to shift load in real time—no code deploy needed.
Sticky Sessions via DNS
Pure DNS can’t guarantee session affinity, but you can create regional subdomains (us.yourdomain.com, eu.yourdomain.com) and let users pick. Store preference in cookie for return visits.
RUM-Based Steering
Real User Metrics (RUM) JavaScript reports actual browser latency to endpoints. GeoDNS provider adjusts map hourly, sending traffic to fastest-performing PoP, not necessarily geographically closest.
Legal & Compliance
Some data must stay in-country (health, finance). Use GeoDNS to fence EU users to Frankfurt, US users to Virginia. Combine with AWS IAM policies to block cross-border S3 replication.
Pitfalls
- Over-steering: tiny latency gains offset by cache fragmentation
- Resolver concentration: all Nigerian users may hit Johannesburg cache, skewing metrics
- EDNS subnet privacy: some resolvers disable it, falling back to resolver country
Cost vs ROI
GeoDNS adds $50-$200/month but can reduce page load 200 ms, improving conversion 2-3%. For a $1 M e-commerce store, that’s $20k extra revenue—400% ROI.