The buzz word “Elastic” is the key player in cloud computing . The technique which amazon has adopted is termed as “Elastic IP” .
Imagine a scenario that you are running an EC2 instance with non-elastic IP (dont confuse that your EC2 instnace has dynamic ip and every time if you restart OS in EC2 it gets new IP, that is absolutely wrong !!) as EC2 do get the Fix IP
The only difference between the FIX-IP and Elasitc-IP is that Fix IP terminate when you terminate the Ec2 instance and if you start new fresh instance you get new IP .
So in above scenario if your webserver dies and you suddenly needed to start new EC2 instance , and if you dont have elastic IP , you have to update your DNS for the new Ec2’s IP which may take some time .. around 1-72 hrs DNS propogation.
If you already had ElasticIP you donot need to update your DNS and just attach that elastic Ip to your newly started EC2 .
More precisely as :
Elastic IP addresses are static IP addresses designed for dynamic cloud computing. Elastic IP addresses are associated with your account, not specific instances. Any elastic IP addresses that you associate with your account remain associated with your account until you explicitly release them. Unlike traditional static IP addresses, however, elastic IP addresses allow you to mask instance or availability zone failures by rapidly remapping your public IP addresses to any instance in your account.
Note: To ensure customers are efficiently using elastic IP addresses, we impose a small hourly charge when these IP addresses are not mapped to an instance. When these IP addresses are mapped to an instance, they are free of charge.