How an A record works
An A record is the entry in your DNS zone that maps a name to the numeric address of a server. When somebody types your domain, the lookup ends here: the A record names the machine that should answer, and the browser connects to it. The A stands for address, and it is the most basic record a working website needs.
A zone normally holds several. There is usually one for the bare domain and one for the www version, plus others for subdomains that point somewhere else entirely — a shop on a hosted platform, a help centre on a support tool. Where the destination is another name rather than a numeric address, a CNAME record does the job instead. Addresses written in the newer, longer format live in AAAA records, which behave the same way.
Why the A record matters
It is the record that decides whether your website exists at all. Point it at the wrong machine and visitors get somebody else’s page, a hosting holding screen, or a security warning because the certificate on that server was never issued for your domain. Remove it and the name simply does not resolve.
It is also the record most often edited by people who are not thinking about the rest of the zone: a developer pointing the domain at a new build, a platform’s setup wizard asking you to paste an address into a box. Those edits are correct in isolation and still cause damage, because moving the website does not move the mail. That is the MX record‘s job, and almost everyone assumes otherwise the first time.
Common mistakes with A records
Duplicate records for the same name are the quiet one. Two entries for the same host send visitors to both machines in turn, so the site works for some people and fails for others, and the fault reads as intermittent rather than structural. It is a common leftover from a migration where the new record was added before the old one was removed.
Stale records are the other. A subdomain nobody remembers keeps pointing at a former server, which happily serves an outdated copy of the site for search engines to index and customers to find. Worse still is a record aimed at a server you no longer rent, because that address will eventually belong to someone else entirely, and your name will be pointing at their content.
Getting A records right
Keep a written list of every A record in the zone, what it points at and who asked for it. Before repointing anything on a live site, shorten its time to live so a mistake can be reversed quickly rather than sitting in caches for the rest of the day. After the change, load the site over both http and https and inspect the certificate, because a new server needs its own certificate issued for your domain and the address change alone does not provide one.
Decide once whether the canonical version of your site is the www form or the bare domain, then make the other redirect permanently to it instead of serving a second working copy. Two addresses that both answer are two versions of the site for search engines to choose between, and that choice is better made by you.