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Study finds DNS TTL cuts have little impact on cloud failover speed

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A final-year dissertation measuring multi-cloud DNS failover over three months found that lowering DNS TTL values does not significantly reduce recovery time during cloud outages. The researcher tested a Flask app deployed across AWS and Azure, simulating nine failover events across three TTL settings of 60, 120, and 300 seconds. Results showed that Route 53's health check detection time of roughly 48 seconds remained constant regardless of TTL, because detection is governed by the provider's internal polling logic, not the TTL value. Propagation time, where TTL does matter, varied widely between resolvers — Cloudflare oscillated for over 325 seconds at TTL=300 while Google DNS stabilised far sooner. The findings suggest engineers should prioritise tuning health check intervals and failure thresholds first, as these set the hard floor for recovery time, with TTL adjustments offering only marginal gains.

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