A company has a business-critical standard three-tier highly available web portal in AWS. The web tier runs on different types of Amazon EC2 family. The application tier runs on one set ofEC2 family, and the database tier runs on Amazon RDS. The company’s leadership team asked the Solutions Architect to reduce the costs of this solution without any impact on the company`s business. Which of the following options is the most cost-effective while maintaining reliability and a high availability?

Answer options:

A.Use Compute Savings Plans for the web tier, EC2 Instance Savings Plans for the application tier, and Reserved Instances for the database tier.
B.Use Compute Savings Plans for the web tier, EC2 Instance Savings Plans for the application tier and the database tier.
C.Use EC2 Instance Savings Plans for the web tier, Compute Savings Plans for the application tier and the database tier.
D.Use EC2 Instance Savings Plans for the web tier, Compute Savings Plans for the application tier, and OnDemand Instances for the database tier.

Answer: A
Option A is CORRECT. Compute Savings plans automatically apply to EC2 instance usage regardless of instance family, size, AZ, region, and OS. The web tier consists of multiple types of instance family. EC2 Instance Savings Plans automatically reduce cost on the selected instance family in that region regardless of AZ, size, OS, or tenancy. Since application tiers use the same set of instance families. The savings plan doesn`t support the RDS. So, Reserved instances are the best option.
Option B is incorrect because Savings plans don’t support RDS. To Reserved option is the best option.
Option C is incorrect because EC2 Instance Savings Plans for the web tier don`t support multiple instance families.
Option D is incorrect because On-demand instances won’t save cost for the long run.
References:
https://aws.amazon.com/savingsplans/
https://go.forrester.com/blogs/aws-savings-plans-what-they-are-and-why-you-should-care/