Ephemeral is the default
Most cloud providers hand out a temporary public address at creation time. It survives a reboot but not a stop/start cycle or an instance replacement. If your DNS points at that address, a routine resize can take the site offline until you notice and edit the record again.
Reserve before you configure
Allocate a static address while the instance is still being built, then attach it. Update DNS only after you have confirmed the address is attached and the web server responds on it. Document the address alongside the instance name so the next person does not have to guess.
curl -I https://wordpressmentor.com
dig +short wordpressmentor.com AOne caveat: a reserved address that is not attached to a running instance may still be billed. Release addresses you no longer need, but never release one that a live DNS record still references.