DNS Cache: how it works, TTL, and how to monitor it in production

▤ Summary

This article explains how DNS cache works across browser, operating system, resolver, and authoritative layers. It shows how TTL limits cache duration, why positive and negative caching behave differently, and why DNS changes can appear slow to propagate. It also outlines practical ways to inspect and flush caches and recommends lowering TTL before planned DNS changes. The piece highlights monitoring signals such as hit ratio, lookup latency, and NXDOMAIN/SERVFAIL rates to catch issues early. It closes by framing DNS cache as a critical operational layer that affects availability, troubleshooting, and security.

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