Domain · DNS
Domain / Domain Name System
What is a domain?
- Domain = the address people remember
- DNS = translates names into IP addresses
- The internet's phone book
What domains and DNS really change is separating the address from the server. If you give customers an IP address directly, that address dies the moment you move servers. With a domain in front, visitors keep reaching the same address even when the server behind it changes from local hosting to the cloud. In a migration, what the company actually changes is a single record line, not the server, and the address printed on business cards and catalogs never needs to be touched.
In practice, you work with two layers. At the registrar where you bought the domain (Gabia, Whois, etc.), you decide where the nameservers point, and inside those nameservers you write the records. Each record type does a completely different job — A (domain→IP) and CNAME (domain→another domain) for the web, MX for receiving email, and TXT for verifying Google Workspace ownership or for spam protection (SPF). A root domain generally can't have a CNAME, so you use an A record or a provider-specific alias feature. Each record also carries a TTL (how long it stays in cache), usually 3,600 seconds. If a server migration is scheduled, the standard practice is to lower it to 300 seconds a day ahead. Note that DNS only points the way — it is not responsible for the https padlock (the SSL certificate).
The most common mishap is moving a website and rebuilding the records from scratch, forgetting the MX and TXT records. The site opens fine, so nobody notices until the sales team says, 'We haven't received a single quote request email in two days.' An expired domain takes a site down as often as a server failure does — if the payment card expires and the person in charge has left, the address suddenly stops working one day. People also tend to just wait for 'propagation to finish' when a site won't open, but the cause is usually stale cache on your own PC or carrier, so check first from a different network or an external lookup site.
Jaryong KooMarketing PhD and authority in AI, data analytics, and personal branding
John KimAuthor of B2B Marketing Design and CEO of Nanum ConsultingDNS (Domain Name System) was designed by Paul Mockapetris in 1983. It was created so that the fast-growing number of internet addresses could be managed with names people can remember.
Consider a hypothetical case. Company A, a health-supplement distributor with 38 employees and KRW 21 billion (≈ US$15,711,500) in annual revenue, decided to move its hosting from a local provider to the cloud while redesigning its website for the first time in six years. But the domain was registered under the personal account of an employee who left 10 years ago, and 40 company email accounts used that same domain. Launch was three weeks away.
- Park, a senior manager in Corporate Services, called the registrar's customer center and applied for an ownership transfer. Sending the business registration certificate and the CEO's ID and getting them verified took 9 days on its own, and that was also when the team learned the domain had only 11 months left before expiry.
- The CEO of the outside development firm made it clear: 'We'll handle the web, but never touch the mail records.' So Park, a senior manager, captured the admin screen and copied the 4 MX and 2 TXT records exactly as they were into a spreadsheet.
- Two days before the cutover, the developer's project lead lowered the A record's TTL from 3,600 to 300 seconds. The reason: if something went wrong, they couldn't afford to wait an hour to roll back.
- At 11 p.m. on Sunday, the team switched the A record to the new server IP, and Kim from marketing checked access on both mobile LTE and the office Wi-Fi. Only 3 office PCs still showed the old page, so they flushed the DNS cache.
- No emails were lost during the cutover, and the site was down for 12 minutes. Afterward, the company renewed the domain for five years up front, set up automatic payment on the corporate card, and moved the admin account to a shared Corporate Services mailbox.