DNS

DNS is the internet’s naming system. It turns a name such as www.example.com into records that tell clients where to connect or how to handle mail, verification, and other services.

The common record types are A, AAAA, CNAME, MX, TXT, and NS. For web work, the mistake is usually not the record type itself but time: cached records and TTLs mean a change may not appear everywhere at once.

DNS is quiet infrastructure. Nobody thinks about it when it works, and everyone blames it when a migration gets weird.