You have a distributed application that periodically processes large volumes of data across multiple Amazon
EC2 Instances. The application is designed to recover gracefully from Amazon EC2 instance failures. You are
required to accomplish this task in the most cost-effective way. Which of the following will meet your
requirements?

A.
Spot Instances

B.
Reserved instances

C.
Dedicated instances

D.
On-Demand instances

Explanation:
Using reserved instances is not the most cost-effective way.
https://aws.amazon.com/blogs/aws/new-scheduled-reserved-instances/ “Scheduled Reserved Instance model
allows you to reserve instances for predefined blocks of time on a recurring basis for a one-year term, with
prices that are generally 5 to 10% lower than the equivalent On-Demand rates.” You can get spot instances
with much lower prices:
https://aws.amazon.com/ec2/spot/pricing/
“Spot instances are also available to run for a predefined duration in hourly increments up to six hours in length
at a significant discount (30-45%) compared to On-Demand pricing plus an additional 5% during off-peak times
for a total of up to 50% savings.”