What does "Public IP/Elastic IP Data Transfer" mean?

Question

Amazon AWS calculator says data transfer in is free to ec2 instances, but it also has an input box for "Public IP/Elastic IP Data Transfer" saying:

If you choose to communicate using your Public or Elastic IP address or Elastic Load Balancer inside of the Amazon EC2 network, you will pay Intra-Region Data Transfer rates even if the instances are in the same Availability Zone. For data transfer within the same Availability Zone, you can easily avoid this charge (and get better network performance) by using your private IP whenever possible.

Say I have a single instance handling requests from the Internet using a public or elastic IP. Will I pay for incoming traffic?

If so, is there a way for ec2 instances to communicate with the Internet without a public/elastic IP?

Answer 1

Say I have a single instance handling requests from the Internet using a public or elastic IP. Will I pay for incoming traffic?

No. Inbound data transfer from the Internet is now (as of late 2011) free.

If so, is there a way for ec2 instances to communicate with the Internet without a public/elastic IP?

There is none, so you will always pay for outbound data transfer to the Internet.

You can see the full schedule of fees here. You should double check the regions you care about and the exact details.