You currently have a set of EC2 Instances in a private subnet that communicates to the internet via a NAT instance. You now plan to start using a NAT gateway and replace the usage of the NAT Instance. During the transition , which of the following needs to be noted

Answer options:

A.You can safely do the transition since during the transition , the existing connections will be moved from the NAT instance to the gateway.
B.The existing connections to the NAT instance will go through a connection draining period, hence there will be no disruptions to the existing service.
C.There will be a slight disruption which needs to be accounted for because the current connections to the NAT instance will be dropped.
D.It is not possible to replace a NAT gateway with a NAT instance.

Answer - C
The AWS documentation mentions the following
If you change your routing from a NAT instance to a NAT gateway, or if you disassociate the Elastic IP address from your NAT instance, any current connections are dropped and have to be re-established. Ensure that you do not have any critical tasks (or any other tasks that operate through the NAT instance) running.
For more information on NAT gateways, please visit the below link:
http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/vpc-nat-gateway.html