TTL Too High: When Cache Becomes a Problem

A poorly sized TTL can turn a simple migration into a multi-day nightmare.

TTL (Time To Live) determines how long DNS resolvers cache your records. A high TTL (24-48h) reduces load on your DNS servers and improves performance, but drastically slows change propagation. During a migration or incident, a TTL of 86400 seconds means some users will see the old IP for 24h after your change. Understanding TTL tradeoffs is essential for effective DNS management.

Symptoms of TTL Problems

  • After a DNS change, some users still see the old IP
  • Failover to backup server takes hours instead of minutes
  • Tests from different locations give inconsistent results
  • Migration planned for 1h actually takes 24h

Why TTL Causes Problems

  • Registrar default TTL: Many registrars configure 24h TTL by default without you knowing.
  • No pre-migration reduction: You changed the IP without reducing TTL beforehand.
  • Intermediate cache: Some resolvers don't strictly respect TTL and cache longer.

Diagnosis and Correction

  1. Check current TTL: dig example.com and look at the value in TTL column.
  2. Displayed TTL is time REMAINING before expiration, not configured value.
  3. To know configured TTL, query authoritative NS directly: dig @ns1.example.com example.com
  4. Plan: reduce TTL 48h BEFORE migration, then raise it after.

TTL Monitoring with MoniTao

MoniTao helps you manage TTL:

  • Visibility on TTL of your critical records
  • Alert if TTL is unusually high before a planned migration
  • Verification of effective propagation after change

TTL Strategy

  • Daily TTL (3600-86400s) for stable records
  • Short TTL (300-600s) for services needing fast failover
  • Reduce to 300s 48h before any planned migration or change
  • Progressively raise TTL after confirming success

FAQ - TTL Problems

Can I force immediate propagation?

No. You don't control third-party resolver caches. You must wait for TTL expiration.

What TTL for an e-commerce site?

3600s (1h) is a good compromise. Short enough for reasonable failover, long enough for performance.

Does TTL affect SEO?

Indirectly. High TTL slows migration, prolonging potential unavailability that impacts SEO.

Do some resolvers ignore TTL?

Yes, some have minimum (e.g., 60s) or maximum. But major resolvers (Google, Cloudflare) respect TTL well.

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