Amey-Thakur DNS fundamentals
DNS is the first hop of almost every request and the last place people look when something breaks. Most DNS incidents are not exotic: a TTL was longer than the change window, a record was edited at a provider nobody queries, or a stale cache still holds the old answer.
Method
- Know which record answers which question. A and AAAA map a name to an address, CNAME aliases one name to another, MX routes mail, TXT carries verification and policy, and NS delegates a zone. Picking the wrong type is the most common misconfiguration, and a CNAME at the zone apex is invalid in plain DNS, so it needs the provider's ALIAS equivalent.
- Treat TTL as your change window. A record's TTL is how long resolvers may keep the old answer, so a 24-hour TTL means a 24-hour tail after any change. Lower it well before a planned move, make the change, then raise it again once the new value is stable.
- Verify at the authoritative server, not just locally. Query the zone's own nameservers to see the truth, then a public resolver to see what the world currently gets. A difference between the two is cache, not misconfiguration, and it clears with time rather than with more edits.
- Confirm you are editing the zone that is live. Domains often have records at a registrar, a DNS host, and a CDN, and only the delegated nameservers matter. Check the NS records before spending an hour editing a zone nobody queries.
- Give DNS its own redundancy. Multiple nameservers across providers survive one provider's outage, and health-checked records steer traffic away from a dead endpoint (see multi-region-design). DNS is a dependency like any other.
Boundaries
- DNS resolves names to addresses; it does not load balance with any precision. Round-robin records spread requests roughly at best, and caching skews the split (see load-balancing for real control).
- Propagation is a misnomer: nothing pushes, everything expires. If a change is not visible, suspect a cached TTL, not a stuck record.
- Registrar operations such as transfers, locks, and expiry sit outside the zone and can take days regardless of your TTLs.