A Record (Address Record)

An A record (address record) maps a hostname to a 32-bit IPv4 address. It is the record that tells browsers which server to connect to when someone visits example.com over IPv4.

Why it matters

If the A record is missing, wrong or points to a server that is down, visitors cannot reach your site even though everything else is configured correctly. A hostname can have several A records at once; resolvers return them all, and clients typically try them in varying order, which gives a crude form of load distribution and failover. It does not remove dead servers automatically, so a dead IP in the set still causes intermittent failures.

Example

example.com.     300  IN  A  203.0.113.10
example.com.     300  IN  A  203.0.113.11
www.example.com. 300  IN  A  203.0.113.10

Check it with dig +short example.com A. The addresses shown here come from the 203.0.113.0/24 documentation range.

Common mistakes

Pointing the A record at a private address such as 192.168.x.x or 10.x.x.x, which only works inside your network.
Updating the A record for the apex but forgetting www, or the reverse.
Leaving an old IP in a multi-record set after migrating, causing failures for some visitors only.
Forgetting that IPv6 users use the AAAA record. A stale AAAA can break a site that looks fine on IPv4.

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