Lowering your DNS TTL will not speed up your failover, and here is the data showing why

Short summary

A three-month empirical study of multi-cloud DNS failover shows that lowering TTL does not meaningfully speed up recovery. Detection time — governed by Route 53's internal health check polling — was ~48 seconds and constant across TTL configs of 60s, 120s, and 300s. TTL only affects propagation time, which is resolver-dependent and variable. The practical advice: tune health check interval and failure threshold first, then lower TTL for tail optimization.

• •DNS failover RTO is dominated by health check detection time (~48s), not TTL — lowering TTL from 300 to 60 saves negligible time
• •TTL only affects propagation time, which varies dramatically by resolver (Cloudflare oscillated 325s vs Google DNS much faster at TTL=300)
• •Tune health check interval and failure threshold first; lower TTL second for tail optimization

Generated with AI, which can make mistakes.