What is an Elastic IP address?
An Elastic IP address is a static IP address designed for dynamic cloud computing. An Elastic IP address is associated with your AWS account and you can use it until you release it.
An Elastic IP address is a public IPv4 address that is reachable from the internet. If your instance does not have a public IP address, you can associate an Elastic IP address with your instance to enable communication with the Internet. For example, If an instance goes down within AWS, Using An Elastic IP you can maintain your IP address and communication with your AWS account.
Private and Public IP Addresses in AWS
Private IP Addresses
A private IPv4 address is an IP address that is not reachable over the Internet. Private IPs enables the communication between instances in the same VPC. Amazon allocate private IPv4 addresses to instances using DHCP protocol.
When you launch an instance, a primary private IPv4 address is assigned for the instance, and an internal DNS hostname that resolves to the primary private IPv4 address (For example, ip-10-201-70-12.ec2.internal).
Each instance has a default network interface (eth0) that is assigned the primary private IPv4 address. A private IPv4 address remains associated with the network interface when the instance is stopped, hibernated and started. It is released when the instance is terminated.
Public IP Addresses
A public IPv4 is an IP address that is reachable from the Internet. Public IPs address enables the communication between your instances and the Internet. Each instance that receives a public IP address is also given an external DNS hostname (For example, ec2-201-0-103-25.compute-1.amazonaws.com).
A public IP address is assigned to your instance from Amazon’s pool of public IPv4 addresses, and is not associated with your AWS account. When a public IP address is disassociated from your instance, it is released back into the public IPv4 address pool and you cannot reuse it.
Note: You can use an Elastic IP address for persistent public IP address that can be associated to your instances as you require.