Domains and DNS Basics

Build the mental model

A domain like thutatech.com is really made of labeled pieces, and learning to read them helps everything else about hosting make sense.

DNS is the system that maps these human-readable names to real servers. The two record types you will run into constantly are A records, pointing a name at an IP address, and CNAME records, pointing a name at another name. The Networking tutorial on this site covers the full record type list and resolution mechanics in depth.

• Registrar -- where you buy and legally own a domain name (Namecheap, GoDaddy)
• Host -- where your actual application or files live
• DNS -- the bridge connecting the registrar's domain to the host

Domain

The registered name an organization owns -- like thutatech in thutatech.com.

Subdomain

A free subdivision of a domain -- like learn in learn.thutatech.com.

DNS

The system that maps domain names to real internet resources like IP addresses.

ANATOMY OF A HOSTNAME
---------------------
      learn   .   thutatech   .   com
        |            |            |
    subdomain      domain         TLD
   (optional)    (registered)  (top-level)

 REGISTRAR (you own the name)   vs   HOST (app lives here)
   e.g. Namecheap, GoDaddy             e.g. Vercel, AWS, DigitalOcean
              |                                    |
              +--------- DNS record links them ----+

Connect it to a real scenario

The parseHostname function below takes a full hostname string and splits it into its subdomain, domain, and top-level domain pieces, the same breakdown this lesson just walked through in prose. It splits the hostname on every dot, then reasons from the right side: the very last piece is always the TLD, the piece before that is the domain, and anything left over at the front, possibly more than one label, is treated as the subdomain. Running it against thutatech. com, learn. thutatech.

com, and api. staging. thutatech. com shows the pattern clearly: a bare domain has no subdomain at all, a single label like learn becomes the subdomain, and multiple labels like api.

staging get joined back together as one subdomain value. This is a simplified parser meant to build intuition, not a production-grade implementation; real hostname parsing has extra edge cases, such as TLDs that are themselves two labels like co. uk, which this simple version does not handle. The goal here is pattern recognition: once you can mentally split any hostname into these three pieces on sight, DNS records and hosting configuration both make noticeably more sense.

• Reading a hostname as subdomain, domain, and TLD underlies most hosting concepts
• DNS maps a name to an IP address (A record) or to another name (CNAME)
• Owning a domain (registrar) and hosting an application are two separate things

Try the working example

function parseHostname(hostname) {
  const parts = hostname.split(".");
  if (parts.length <= 2) {
    return { subdomain: null, domain: parts[0], tld: parts[1] };
  }
  const tld = parts[parts.length - 1];
  const domain = parts[parts.length - 2];
  const subdomain = parts.slice(0, parts.length - 2).join(".");
  return { subdomain, domain, tld };
}

const hosts = ["thutatech.com", "learn.thutatech.com", "api.staging.thutatech.com"];

for (const host of hosts) {
  const { subdomain, domain, tld } = parseHostname(host);
  console.log(`${host} -> subdomain: ${subdomain}, domain: ${domain}, tld: ${tld}`);
}

thutatech.com -> subdomain: null, domain: thutatech, tld: com
learn.thutatech.com -> subdomain: learn, domain: thutatech, tld: com
api.staging.thutatech.com -> subdomain: api.staging, domain: thutatech, tld: com

MDN Glossary: Domain name — Cloud & Deployment