In this section, we will begin with a little history lesson by talking about classic EC2s, and comparing them with EC2s that are launched in a VPC.
EC2s were first introduced by AWS back in 2006. Back then, there was only one big public network in which to launch your instances. Every instance was automatically assigned a public and private IP address, controlled by AWS. If you stopped your instance for any reason, AWS took back your IPs, and when you started it up again, you got new ones.
Since every instance had a public IP address, they were all essentially public. So you had to rely on security groups to restrict access to your databases and other instances that you wanted to keep private, and the security groups only allowed you to specify inbound rules. All outbound traffic was always allowed. In 2009, AWS launched VPCs and encouraged customers to launch instances in these virtual private networks, instead of in the big public network. EC2s that...