mediumConceptMidSeniorStaff
You are about to change the address a hostname points to. What does the TTL actually promise you, and why do clients keep reaching the old address anyway?
5 min readUpdated 2026-08-15Target archetype: Big Tech, Enterprise Captive, Product Startup
Answer
Short answer
A TTL is an upper bound on how long a resolver may cache a record, not a promise about when clients will notice a change. Lowering it only takes effect after one old TTL has elapsed, negative answers are cached under a different rule, and pooled connections keep using an address they resolved hours ago.
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