See how a DNS TTL trades resolver cache hit ratio and query spend against how fast a record can fail over.
A caching resolver queries you roughly once per TTL no matter how many clients it serves, so authoritative load is resolver count divided by TTL — halving the TTL doubles your query bill while halving the time a change takes to land. Negative answers are cached separately under the SOA minimum, so a typo in a hostname can persist long after the record exists. TTL is the only DNS knob that directly buys failover speed, and it is paid for in authoritative query volume and cost. Query pricing varies by provider and by zone type, so confirm the current per-million rate with your DNS provider.
Cloud DNS TTL
authoritative queries per second = distinct resolvers ÷ TTL; resolver cache hit ratio = 1 − authoritative rate ÷ client lookup rate; worst-case change time = TTL + refresh skew.
authoritative queries per second = distinct resolvers ÷ TTL; resolver cache hit ratio = 1 − authoritative rate ÷ client lookup rate; worst-case change time = TTL + refresh skew. A caching resolver queries you roughly once per TTL no matter how many clients it serves, so authoritative load is resolver count divided by TTL — halving the TTL doubles your query bill while halving the time a change takes to land. Negative answers are cached separately under the SOA minimum, so a typo in a hostname can persist long after the record exists.
TTL is the only DNS knob that directly buys failover speed, and it is paid for in authoritative query volume and cost. Query pricing varies by provider and by zone type, so confirm the current per-million rate with your DNS provider.
This calculator takes 6 inputs: Record TTL, Distinct resolvers seen, Client lookups per second, Price per million authoritative queries, Resolver refresh skew, SOA minimum (negative cache TTL). The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.