AWS Elastic IP Addresses                                

What happens when all the DNS servers out there have your old address and cannot find your site with the new server?               

 

Elastic IP Adress is a public IP address assigned to your account that can be substituted for the temporary public IP address that’s assigned to your instance at launch-time. You request an Elastic IP address from AWS, and it’s provided to you so that you can assign a permanent IP address to your new instances. You can then create a public DNS entry with your URL (say, www.example.com) and the Elastic IP address AWS assigned to your account.                                              

 

An Elastic IP address works in a straightforward manner:

1. You request an Elastic IP from AWS. Within a couple minutes, you receivea new Elastic IP. This address still comes from the general Amazonpublic IP address range, but it’s assigned for your persistent use. By default, you’re limited to five Elastic IP addresses. You can obtain moref rom Amazon, but it generally rations Elastic IP addresses because they’re part of Amazon’s fixed pool of public IP addresses, and it doesn’twant to assign them to an account that won’t use them.

2. You assign the Elastic IP address to an instance you run. You can make the assignment at launch-time or request it after the launch. If it’s the former, when the instance is available, it will have the Elastic IP address; if it’s the latter, it may take five minutes for the substitution to take place. Note that the formerly assigned general public IP address returns to AWS and is subsequently assigned to a new instance.

3. You run the instance with the Elastic IP address. Traffic flows to the address and then to your instance.

 

That’s it! You’re running a persistent Elastic IP address. Keep a couple pointsin mind:

✓ If, for some reason, you want to release the Elastic IP address from aninstance, AWS assigns a new public IP address to the instance from the overall Amazon address pool. It almost certainly isn’t the same public IP address that the instance was initially assigned.

✓ If you decide that you no longer want an Elastic IP address, it returns to the unassigned Elastic IP address pool and is subsequently assigned to another account.

 

Elastic IP address pricing

Amazon prices Elastic IP addresses oddly: It imposes no fee for using ElasticIPs — they’re completely free. However, Amazon charges $.005 per hour for unused Elastic IP addresses — addresses that aren’t actively assigned to running instances. This system motivates users to use the Elastic IP addresses they request, because the addresses are limited commodities. Request onlyt he number of Elastic IP addresses that you need, and release them back toAWS if you find that you don’t need them.             

 

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Elastic IP addresses and AWS network scope

Essentially, AWS network scope conforms to the regional delimitations of AWS. The public IP addresses assigned to your instance vary by region, but are global in nature — which is to say, like all public IP addresses, they’re unique and can be accessed by anyone around the world. Instances within any availability zone in a given region can communicate with one another using the private IP address associated with the instances, and, of course, they incur no network traffic fees for that traffic.