In summary, the combination of VPC + Availability Zone + Subnet + private/public ip addresses +security groups are the AWS resources which form the required infrastructure to support EC2 instances ...

AWS expands private cloud networking ... For instance, a network with a public subnet for its web servers and a private subnet for backend databases or application servers, AWS said.

There are any number of tasks within AWS that require the use of subnets. For example, you can't create an EC2 virtual machine (VM) without first defining a subnet within which the VM will operate.

With some exceptions, the EC2 instances residing within an Amazon Web Services (AWS) Virtual Private Cloud (VPC) often require Internet connectivity. The default VPC is automatically configured to ...

­Amazon’s “Virtual Private Cloud,” a cloud computing offering that is more secure than the company’s previous services, is now available to the general public in an open beta trial ...