Another thing to mention is the usage of a Floating IPs.
A Floating IP is an IP address that can be instantly moved from one Droplet to another Droplet in the same datacenter.
Part of a highly available infrastructure is being able to immediately point an IP address to a redundant server. This is now possible with the addition of Floating IPs.
Floating IPs are free to use. However, due to the shortage of IPv4 addresses available, if you reserve an address but don’t assign it to a Droplet, we charge $0.006 per hour for each unassigned, reserved IP. (You can relinquish unused IPs from the control panel.) To keep billing simple, you will not be charged unless you accrue $1 or more.
Hope that this helps!