An application consists of the following architecture:
a. EC2 Instances in a single AZ behind an ELB
b. A NAT Instance which is used to ensure that instances can download updates from the Internet
What could be done to ensure better fault tolerance in this setup? (SELECT TWO.)
 

Answer options:

A.Add more instances in the existing Availability Zone.
B.Add an Auto Scaling Group to the setup.
C.Add more instances in another Availability Zone.
D.Add another ELB for more fault tolerance.

Correct Answer – B and C
AWS Documentation mentions the following:
Adding Auto Scaling to your application architecture is one way to maximize the benefits of the AWS Cloud. When you use Auto Scaling, your applications gain the following benefits:
Better fault tolerance. Auto Scaling can detect when an instance is unhealthy. Then it terminates that instance, and launches an instance to replace it. You can also configure Auto Scaling to use multiple Availability Zones. If one Availability Zone becomes unavailable, Auto Scaling can launch instances in another one to compensate.
Better availability. Auto Scaling can help you ensure that your application always has the right amount of capacity to handle the current traffic demands.
For more information on the benefits of Auto Scaling, please visit the following URL:
https://docs.aws.amazon.com/autoscaling/ec2/userguide/auto-scaling-benefits.html