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

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

C.
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.

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