We use analytics cookies.We use cookies to analyze site traffic and improve your experience.
Loading...
System Design and AI Engineering, by Roni Das. 984 interactive lessons.
Start LearningFoundation · Load Balancing & Proxies
DNS that returns different IP addresses based on the geographic location of the requester. Routes users to the nearest data center for lower latency.
In short
GeoDNS is a DNS configuration that answers the same domain name with different IP addresses depending on where the request comes from, so a user in Frankfurt gets the IP of a European server while a user in Tokyo gets an Asian one. It is used to send each visitor to the closest or most appropriate data center, cutting latency and spreading load across regions.
In short
GeoDNS is a DNS configuration that answers the same domain name with different IP addresses depending on where the request comes from, so a user in Frankfurt gets the IP of a European server while a user in Tokyo gets an Asian one. It is used to send each visitor to the closest or most appropriate data center, cutting latency and spreading load across regions.
Learn it in the course
This page is the free part.
₹1,111 in India$25 everywhere elseonce, for the whole course
The System Design course covers GeoDNS across a run of lessons, not one page. These 4 alone are about 140 minutes of step-by-step reading, every one with a quiz.
Routing on where a client appears to be, why speed and data residency are two different problems, and how wrong the inference actually is.
Latency-based routing sends each user to the region with the lowest measured round trip. Route 53 latency records, geolocation vs geoproximity, and a real lab.
The internet's phone book, how domain names become IP addresses.
How a GSLB decides which region a user reaches, and why the decision takes minutes to arrive even when it is made in microseconds.
all part of
System Design Masterclass
770 lessons · about 287 hours · 18 free to read
₹1,111in India, by UPI
$25everywhere else, by PayPal
It is really nice and good Please join the course
You own this course
Continue with Geolocation Routingpay once,
yours for life
When you type a domain into a browser, your computer asks a DNS resolver for the IP address behind that name. Ordinary DNS gives every caller the same answer. GeoDNS changes the answer based on who is asking, specifically based on their approximate physical location.
The authoritative DNS server looks at the source IP of the incoming query, maps it to a country or region, and returns a record from a pool that matches that region. So example.com might resolve to 203.0.113.10 (a server in Virginia) for a request from the United States, and to 198.51.100.20 (a server in Singapore) for a request from Indonesia.
GeoDNS is a routing decision made at name-resolution time, before any actual connection to your servers happens. It does not move data or proxy traffic. It only hands out a different address so the user connects directly to a server that is close to them.
The key input is the client IP seen by the authoritative server. In most cases that is the IP of the user's recursive resolver (for example their ISP or a public resolver like 8.8.8.8), not the user's own device. The DNS server matches that IP against a geolocation database such as MaxMind GeoIP2 to guess a location, then picks the closest configured pool of records.
Because the resolver IP is used, accuracy depends on the user querying a nearby resolver. If someone in India uses a resolver hosted in the US, GeoDNS may route them to a US server. The EDNS Client Subnet extension (ECS, RFC 7871) fixes much of this by letting the resolver forward a truncated version of the real client subnet, so the authoritative server sees roughly where the user is.
TTL matters a lot. A short TTL such as 30 to 60 seconds lets you reroute users quickly during a regional outage, but it increases DNS query volume. A long TTL means clients cache the regional IP for hours and ignore later geo decisions until the cache expires.
Many GeoDNS systems also fold in health checks. If the closest region is failing its health check, the authoritative DNS server returns the next-best region instead, which turns GeoDNS into a basic global failover mechanism rather than pure proximity routing.
Reach for GeoDNS when you run servers in more than one region and want each user to hit the nearest one for lower latency, or when you need data residency, so European users land on EU infrastructure for GDPR reasons. It is also a cheap way to do active-active multi-region failover at the DNS layer.
The big limitation is granularity. Geolocation by resolver IP is approximate, you cannot route on real client load, and DNS caching means routing decisions are sticky for at least one TTL. GeoDNS also cannot react within a single connection, since the decision is already made by the time the TCP handshake starts.
For latency-sensitive global traffic, Anycast often beats or complements GeoDNS. With Anycast the same IP is announced from many locations and the network routes the user to the nearest one, with no dependence on geolocation databases or DNS caching. A common production pattern is GeoDNS for coarse regional steering plus Anycast inside each region for fine-grained edge selection.
Suppose you run a SaaS app with clusters in us-east-1 (Virginia), eu-west-1 (Ireland), and ap-south-1 (Mumbai). You configure GeoDNS on app.example.com with three pools, one per region, and attach an HTTP health check to each.
A user in Pune queries DNS. Their ISP resolver, located in India, hits your authoritative DNS. The geo lookup maps the resolver IP to India, so the server returns the Mumbai cluster IP. The user connects to a server roughly 150 km away instead of one across an ocean, and round-trip latency drops from around 250 ms to under 30 ms.
Now the Mumbai cluster fails its health check. Once cached answers expire, the next DNS query gets the Ireland IP from the authoritative server instead. Indian users see slower responses for a short window but the app stays up. Once Mumbai recovers and passes health checks again, GeoDNS resumes sending Indian traffic there.
Amazon Route 53
Offers geolocation and latency-based routing policies that return region-specific records, the managed GeoDNS most AWS multi-region apps use.
Cloudflare
Combines GeoDNS-style geo steering with Anycast so DNS answers and the network path both point users to the nearest edge.
NS1 (IBM)
A dedicated managed DNS provider whose Filter Chain engine does geo, latency, and real-time traffic steering for large content and SaaS platforms.
Netflix
Steers viewers toward nearby Open Connect appliances and regional endpoints using DNS-based geo and latency routing on top of AWS.
GeoDNS hands out different IP addresses based on the requester's location, so the routing decision happens at DNS resolution time and depends on geolocation data plus DNS caching. Anycast announces a single IP from many locations and lets the network route the user to the nearest one at the BGP layer, with no DNS-level geo logic. They are often used together: GeoDNS for coarse region selection and Anycast for edge selection within a region.
In classic DNS the authoritative server only sees the IP of the user's recursive resolver, not the user's device. If someone uses a distant public resolver, GeoDNS geolocates that resolver instead of the user. The EDNS Client Subnet extension (RFC 7871) reduces this by passing a truncated client subnet to the authoritative server, giving a much better location estimate.
Only at a coarse, regional level. It splits traffic by geography and, with health checks, can fail over to another region, but it cannot see real-time server load or balance within a region. For per-request balancing you still need a load balancer (such as an Application Load Balancer or NGINX) behind the regional IP that GeoDNS returns.
A short TTL of 30 to 60 seconds lets you reroute users quickly during a regional outage at the cost of more DNS queries. A longer TTL of several minutes or more reduces query load but makes routing decisions sticky, since clients cache the regional IP and ignore newer geo or health changes until the cache expires.
It helps but is not bulletproof. Combined with health checks it will stop handing out the IP of a failed region, but clients that already cached that IP keep using it until the TTL expires, and connection-level failures are not detected by DNS. For fast, reliable failover most teams pair GeoDNS with short TTLs, Anycast, and client-side retry logic.
DNS
The phonebook of the internet. Translates human-readable domain names (google.com) into IP addresses that computers understand.
Global Load Balancer
A load balancer that routes users to the nearest data center or region based on geography, latency, or health. DNS-based (Route 53, Cloudflare) or anycast-based.
CDN
A network of servers distributed globally that caches content close to users. Netflix uses CDNs to stream video from servers near you, not from one central location.
Proxy
An intermediary server that sits between the client and the destination server. Forward proxies act on behalf of clients; reverse proxies act on behalf of servers.
Reverse Proxy
A server in front of your web servers that receives every request first, passes it to one of them and returns the answer. It handles TLS, load balancing, caching and routing, and hides the servers behind it.
DNS Record Types
Different types of DNS records map domains to resources: A records point to IPs, CNAME aliases one domain to another, MX routes email, TXT stores verification data.
This page explains the idea. The "Geolocation Routing" lesson builds it up step by step, with diagrams. It is part of the System Design Masterclass course, which has 770 lessons. 18 of them are free to read. You pay once and keep it for life, with no subscription.
Open the Geolocation Routing lessoncourse 1
From absolute beginner to principal engineer, drawn step by step.
Asked about GeoDNS in an interview?
Each question has why it is asked, a full answer, what the interviewer listens for, the follow-ups, the common mistakes and a diagram (268 diagrams in all). A PDF you keep, junior to staff level.
India: UPI, cards or netbanking through Razorpay. Elsewhere: card or PayPal. Download at once from My packs.
