Apache by default logs every interaction.
This is normally fine, until you get a large volume of traffic.
The log format has a value - %h - in it which means "hostname".
This means that your server performs a DNS lookup of every IP address that hits the system.
During high load, this can cause the server to hang - as DNS lookups typically have a 30 second timeout.
Instead, amend the %h flag to %a (IP address) to stop the DNS lookups and keep your servers up.
