A website is hosted on two EC2 instances that sit behind an Elastic Load Balancer. The website`s response time has been slowed down dramatically, and customers are placing fewer orders due to the wait time. Troubleshooting showed that one of the EC2 instances had been failed and only one instance is running now. What is the best course of action to prevent this from happening in the future?

Answer options:

A.Change the instance size to the maximum available to compensate for the failure.
B.Use CloudWatch to monitor the VPC Flow Logs for the VPC, the instances are deployed in.
C.Configure the ELB to perform health checks on the EC2 instances and implement auto-scaling.
D.Replicate the existing configuration in several regions for failover.

Correct Answer: C
Option C is correct. Using the elastic load balancer to perform health checks will determine whether or not to remove a non-performing or underperforming instance, and have the auto-scaling group launch a new instance.
Option A is incorrect. Increasing the instance size doesn’t prevent the failure of one or both the instances. Therefore the website can still become slow or unavailable.
B. Monitoring the VPC flow logs for the VPC will capture the VPC traffic, not the traffic for the EC2 instance. You would need to create a flow log for a network interface.
D. Replicating the same two instance deployment may not prevent instances of failure and could still result in the website becoming slow or unavailable.
References:
https://media.amazonwebservices.com/AWS_Building_Fault_Tolerant_Applications.pdf
https://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/flow-logs.html#working-with-flow-logs