How does DNS work, and what DNS issues have you seen in production?

Summary

A recursive resolver answers a query by asking root servers, then the TLD servers, then the domain's authoritative servers, and caches results for the record's TTL. Record types include A/AAAA (addresses), CNAME (aliases), MX, TXT, NS and SRV.

Longer Answer

Production issues: changes that take hours to propagate because of long TTLs (lower TTLs well before migrations); CNAME at the zone apex not allowed (use provider alias records); expired domains; misconfigured delegation; negative caching of NXDOMAIN; DNS resolver overload inside clusters; split-horizon DNS confusion between internal and external views; and DNS-based failover that clients ignore because they cache longer than the TTL. "It's always DNS" is a joke because DNS sits under almost everything.

Key Points

• Recursive resolution and caching by TTL.
• Common record types.
• Lower TTLs before changes; apex aliases.
• Resolver overload and caching surprises.