How is a private/public IP Address allocated to an Ec2 instance (48/285 technotes for 2015)

Private IP Address:

• Launch an instance - private IP address is allocated using DHCP
  
• Private IP address is not reachable from internet
• Ecah instance has a default Network Interface - which specifies primary private IP address for the instance
• You can specify additional priavate IP address
• secondary IP address can be reassigned from one instance to another
• each instance is provided an internal DNS name
• DNS name is not resolvable from outside the network

Public IP Address:

• Is assigned from a pool of Public IP address.
  
• once de-associated, cannot be reused for the same instance
• cannot manually associate/de-associate public ip address
• when instance is stopped or terminated
• instance associated with Elastic IP address
• If you want the same IP address for the instance, use a Elastic IP address.