Module 1: Foundations

DNS-Based Load Balancing and GeoDNS

Learn about dns-based load balancing and geodns

Duration: 7 minutes
Level: Intermediate
Lesson: 22

DNS as a Traffic Management Tool

DNS doesn't just resolve names — it directs traffic. By carefully crafting DNS responses, you can distribute load across servers, route users to the nearest data center, and automatically remove unhealthy endpoints. This is how Telnyx routes customers to the optimal Point of Presence (PoP) worldwide.

Round-Robin DNS: The Simplest Load Distribution

The most basic approach: return multiple A records for the same hostname:

sip.example.com.    60    IN    A    198.51.100.1
sip.example.com.    60    IN    A    198.51.100.2
sip.example.com.    60    IN    A    198.51.100.3

Clients typically try the first address in the response. DNS servers rotate the order with each query, distributing connections across all three servers.

Limitations:

  • No intelligence: Every client gets every IP, regardless of location or server health
  • Uneven distribution: Clients behind large NATs or corporate proxies look like one client but represent thousands of users — all directed to the same first IP
  • No health awareness: If 198.51.100.2 goes down, it's still returned in DNS responses for the entire TTL period
  • Caching disrupts rotation: A recursive resolver caches the response and serves it (in the same order) to all its clients until TTL expires

Despite these limitations, round-robin DNS is used as a baseline. SRV records (Lesson 19) improve on this with priority and weight fields for more controlled distribution.

Weighted DNS Responses

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