DNS record types

What is a A record?

An A record maps a hostname to an IPv4 address. AAAA does the same for IPv6.

This is the record most people mean when they say "DNS". It answers the only question a browser really has: what address do I connect to?

A name can hold several A records. Resolvers hand them out in varying order, which gives crude load balancing but no health checking — a dead server keeps being offered until you remove its record.

Example

example.com.  300  IN  A     93.184.216.34
example.com.  300  IN  AAAA  2606:2800:220:1:248:1893:25c8:1946

The mistake people make

The TTL on an A record is the length of your next migration. Lower it to 300 seconds a day before you move a service, not on the morning of the move — resolvers are still holding the old value until the previous TTL runs out.

Check the A records on a real domain, with everything else that can quietly break.

Check a domain