DNS & Glossary

TTL (Time To Live)

How long a DNS record may be cached before resolvers must re-query — the dial that trades faster propagation against lower DNS load.

What it is

Every DNS record carries a TTL in seconds. Resolvers cache the answer for that long before asking again. A low TTL (e.g. 300s) propagates changes quickly but increases query volume; a high TTL (e.g. 86400s) is efficient but makes changes slow to take effect.

Plan migrations with TTL

Before moving a service, lower the record's TTL a day ahead so the cut-over propagates within minutes, then raise it again afterwards.

Why it matters

  • TTL directly controls how fast a failover or migration reaches users.
  • It balances DNS query load against change agility.

Common mistakes

  • Leaving a very high TTL in place right before a planned IP change, causing long stale-resolution windows.
  • Setting TTLs so low that DNS query volume and cost spike needlessly.

How WebInspect checks this

  • The Network Inspector reports the TTL of every record it resolves.