Public IPs

In the IPv4 address space, some address blocks are open for the public internet, while others are reserved for private use (for example, within a corporate or home network).

The rules surrounding these address blocks are defined in standards documents like RFC 1918 and RFC 6598.

The important idea for us is that servers in an AWS VPC usually communicate with one another using private IP addresses, and use public IP addresses only to communicate with systems outside the VPC (like the internet).

All of our servers on AWS have private IP addresses, and some will also have public addresses, but only if necessary. The CIDR that we set when we created our VPC, 10.0.0.0/22, falls within one of the private IP address ranges.

Public IPs cost money, so we'll use them sparingly!