How do I host a public domain if I have to DHCP an IP address?

You can use a dynamic DNS service, such as DynDNS or ZoneEdit.

Why can't I connect to my instances public IP address from another instance?

There is a known limitation that prevents direct-addressed instances from contacting NAT-addressed instances through their public IP address. You should use the internal IP/DNS name when communicating between Amazon EC2 instances. This will ensure the lowest latency, highest throughput, and lowest cost network route.

Why do I get an internal (RFC 1918) IP address when I look up a DNS name that I expect to map to my instance's external IP address?

Amazon EC2 instances cannot currently access other instances in the new NAT environment using their public NAT IP address. Instead, they must use the private address.Traffic originating from the Internet must use the public NAT IP address.  Within Amazon EC2, DNS requests for the external DNS name of an instance will resolve to the internal IP address of the corresponding instance

Can I use IPv6?

Amazon EC2 presently supports the ICMP, TCP and UDP protocol families of IPv4-based networking.

Why is Amazon EC2 Using NAT?

Public IP space is a limited resource. Amazon EC2 is adopting NAT to assure that we are able to efficiently make use of our public internet addresses.

Furthermore, the new NAT networking will enable Amazon to deliver new features in the future. For example, some users do not want external addresses. This would allow for non-internet routable clusters, which will further preserve IPs and increase security for those not running public facing servers.

Can I use a static IP in my instances?

Not at present. Your image must be configured as a DHCP client and it will be assigned an IP address. Currently, all instances come with internet- addressable IP addresses. If you enable access through the firewall from the "world", you can address them from anywhere.

How does the instance know its public and private addresses?

From within the instance, issue the following HTTP queries:

To obtain the internal IP address:

curl http://169.254.169.254/2007-08-29//meta-data/local-ipv4

To obtain the public IP address:

curl http://169.254.169.254/2007-08-29//meta-data/public-ipv4