A user is planning to host a web server as well as an app server on a single EC2 instance which is a part of the public
subnet of a VPC. How can the user setup to have two separate public IPs and separate security groups for both the
application as well as the web server?

A.
Launch a VPC instance with two network interfaces. Assign a separate security group to each and AWS will assign a separate public
IP to them.

B.
Launch VPC with two separate subnets and make the instance a part of both the subnets.

C.
Launch a VPC instance with two network interfaces. Assign a separate security group and elastic IP to them.

D.
Launch a VPC with ELB such that it redirects requests to separate VPC instances of the public subnet.

Explanation:
If you need to host multiple websites(with different IPs) on a single EC2 instance, the following is the suggested method
from AWS:
– Launch a VPC instance with two network interfaces
– Assign elastic IPs from VPC EIP pool to those interfaces (Because, when the user has attached more than one network
interface with an instance, AWS cannot assign public IPs to them)
– Assign separate Security Groups if separate Security Groups are needed
This scenario also helps for operating network appliances, such as firewalls or load balancers that have multiple private
IP addresses for each network interface.
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/MultipleIP.html