The difference between elastic IP and public IP in EC2 cloud host

Create a EC2 instance, we can check "automatic distribution of public IP" (the exact words are in English, oh ~), you can not check, and then manually associated elastic IP (EIP), then the two have what difference?

Learn from Amazon Online Technical support:

(1) The EIP belongs to a specific account, can be associated to any instance of the account, but also can be unloaded down to other instances, and after the instance is deleted, the EIP still exists alone. (The allocation of EIP pay attention to the difference between VPC and EC2 EIP, different types of EIP can be associated to their own types of instances, that is, VPC in the EIP can only be used in VPC instances, Classic EC2 can only be associated with the EIP)
(2) While the ordinary public IP is a specific instance, can not unload and reconnect to other instances, when the instance is created, if the check automatically assign public IP, will be created with the instance, the instance is deleted, then deleted, cannot be reused and retained;
(3) There is also a very important feature: the public IP after the instance shutdown and then boot, may change, reboot does not affect (this is the same as the classic EC2 instance of public DNS, may change). And the EIP will never change.
(4) If the instance is created at the beginning, there is Publicip, then the ELASTICIP, both will become ELASTICIP appearance (is covered), when the EIP is released after the association, PUBLICIP will be revealed, but at this time will redistribute Publicip, So Publicip will change.
Therefore, if in the life cycle of the EC2 instance, there is the possibility of downtime and restart, or use EIP to compare insurance


Attention:
1. Today tested in the background to select the instance direct reboot, public IP & Private IP are unchanged.
2. If you stop first, then start, the IP may be changed. For more information on AWS Documentation: