When I stop/restart an EC2 instance, assigned public IP address has changed.
A public IP address is reachable from the internet. You can use public IP addresses
for communication between your instances and the Internet. When launch an EC2 instance,
a Public IP address assigned to reach the instance.
When stop that instance and restart, we get a new Public IP for the same instance.
Public IP gets changed everytime for an instance after stop/start the instance.
To prevent this issue, we assign an Elastic IP address to an instance which doesn't change
after stop/start the instance as many times.
An Elastic IP address is a public IP address that you can allocate to your account. You can
associate it to and from instances as you require, and it's allocated to your account
until you choose to release it.
For more information about Elastic IP addresses and how to use them, see Elastic IP Addresses.