NAT
- Network Address Translation
 
NAT Instances
- Allows EC2 instances in private subnet to connect to the internet.
 - Must be launched in public subnet.
 - Must disable Source / Destination check.
 - Must have Elastic IP attached.
 - Route tables must be configured.
 

NAT Gateway
- AWS managed NAT.
 - Create in a specific AZ and uses Elastic IP.
 - Can only based used by EC2 instances from another subnet.
 - Requires Internet Gateway.
 - No security groups to manage.