The floating IP is required for directly accessing the instance on the internet. It can be used by connecting to the same resource of the instance one-to-one.
When the instance is created, you get an IP address assigned from the specified subnet, and this is called the fixed IP. However, since this address is the address of a private network, it is not accessible on the internet. So if you want to directly access the instance from outside, you must use an IP address which is externally accessible. If the floating IP is used, the address and instance are connected one-to-one, making it directly accessible on the internet.
[Note] To connect a floating IP to the instance, the subnet containing the instance must be connected to the routing table,
and that routing table must be connected to the internet through an internet gateway in order for "connection" action to be carried out.
The following is the features of the floating IP:
[Note] If two instances in the identical VPC use the fixed IP to carry out local communication, no fee is charged.