DNS Based Traffic Steering and Failover Strategies

DNS serves as both a control plane and data plane tool for sophisticated traffic management. Operators leverage DNS for latency based routing (directing users to the nearest datacenter), geolocation steering (routing based on source IP geography), weighted distribution (splitting traffic by percentage), and health checked failover (removing unhealthy endpoints from responses). Amazon Route 53 exemplifies production scale authoritative DNS, handling millions of queries per second with a 100 percent availability SLA and offering all these routing policies with integrated health checking.

Health driven failover typically runs external HTTP or TCP checks at 10 to 30 second intervals with quorum based failure detection requiring 3 consecutive failures before removing an endpoint. The system combines low but not tiny TTLs (30 to 120 seconds) to balance fast failover against cache efficiency and query load. During the October 2016 Dyn attack, a 1+ Tbps DDoS overwhelmed authoritative capacity, disrupting resolution for Twitter, Spotify, and GitHub for hours. This incident drove widespread adoption of multi provider DNS strategies where zones are served by 2 or more independent authoritative providers to eliminate single points of control plane failure.

Advanced mechanisms include split horizon DNS (serving different answers based on query source, useful for internal versus external clients), EDNS Client Subnet (ECS) for improved geo steering accuracy, and apex flattening or ALIAS records to enable CDN style CNAME behavior at the zone root where standard CNAMEs are prohibited. Many large sites maintain 20 to 60 second TTLs on critical traffic steering records, accepting higher query volumes (potentially millions of QPS for popular domains) in exchange for sub minute traffic shift capability during incidents.

💡 Key Takeaways

•Amazon Route 53 handles millions of QPS with 100 percent availability SLA using global anycast; health checks run at 30 second intervals (10 second fast option available) with quorum failure detection

•TTL selection creates direct tradeoff: 30 second TTL enables sub minute traffic shifts but generates 10x queries versus 300 second TTL; CDNs often use 20 to 60 second values on steering records

•Multi provider DNS became standard practice after October 2016 Dyn attack (1+ Tbps DDoS) disrupted major sites for hours, demonstrating single provider risk for authoritative infrastructure

•EDNS Client Subnet improves CDN selection accuracy by 10 to 30 ms for some populations but fragments caches (reducing hit rates by double digit percentages) and leaks client privacy

•Health checked failover with 3 consecutive failures at 10 second intervals takes 30 seconds to detect plus TTL duration to propagate, meaning 60 to 150 second total failover time with typical TTLs

•CNAME chains longer than 2 materially increase tail latency as each hop requires a separate query adding one RTT; keep hot paths to 1 or 2 CNAMEs maximum

📌 Examples

A global service using Route 53 latency based routing with 30 second TTL and 10 second health checks can shift traffic away from a failed region in approximately 60 seconds: 30 seconds to detect (3 failures) plus 30 seconds for caches to expire

Netflix uses multi CDN DNS steering with weighted records and 60 second TTLs, adjusting weights based on real time availability and quality of experience metrics to optimize streaming performance

Microsoft Azure DNS incident in April 2021 showed abnormal traffic patterns increasing query latency and error rates for hours, requiring rapid capacity scaling and traffic engineering to mitigate

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