Unit III · Going live
Domains and DNS, without the fog
Three different companies can be involved in one web address: the registrar you rent the name from, the DNS host that answers questions about it, and the web host that runs the app.
Three jobs
The registrar holds your registration; you tell it which nameservers are in charge of the name, and it records that with the domain name registry. The DNS host runs those nameservers and holds the records. The web host runs the server your records point to. One company can do all three, but when something breaks, knowing which job failed tells you whom to ask.
Records you will meet
An A record points a name at an IPv4 address; an AAAA record at an IPv6 address. A CNAME makes one name an alias of another (for example www pointing at your main name). MX records say where email for the domain is delivered. TXT records hold text, such as email sender rules and ownership checks.
Why changes take time
Every DNS record carries a TTL (time to live) in seconds: how long resolvers may cache the answer. A resolver can keep serving the old answer until its TTL runs out, so a change can take that long to be seen everywhere. A shorter TTL makes changes reach people sooner, but only once answers cached under the old, longer TTL have run out.
Words to know
- Registrar
- where you rent a domain name
- Nameserver
- a server that answers DNS questions for a domain
- A record
- a name pointed at an IPv4 address
- TTL
- how long an answer may be cached, in seconds
Sources
- MDN Web Docs: What is a domain name?
- Cloudflare Docs: DNS record types
- Cloudflare Docs: Time to Live (TTL)
Checked October 17, 2026. Pages on other sites change; if a source no longer says what the lesson says, the source wins.