AWS Certified Solutions Architect – Professional — Question 332

A company wants to run a serverless application on AWS. The company plans to provision its application in Docker containers running in an Amazon ECS cluster.
The application requires a MySQL database and the company plans to use Amazon RDS. The company has documents that need to be accessed frequently for the first 3 months, and rarely after that. The document must be retained for 7 years.
What is the MOST cost-effective solution to meet these requirements?

Answer options

• A. Create an ECS cluster using On-Demand Instances. Provision the database and its read replicas in Amazon RDS using Spot Instances. Store the documents in an encrypted EBS volume, and create a cron job to delete the documents after 7 years.
• B. Create an ECS cluster using a fleet of Spot Instances, with Spot Instance draining enabled. Provision the database and its read replicas in Amazon RDS using Reserved Instances. Store the documents in a secured Amazon S3 bucket with a lifecycle policy to move the documents that are older than 3 months to Amazon S3 Glacier, then delete the documents from Amazon S3 Glacier that are more than 7 years old.
• C. Create an ECS cluster using On-Demand Instances. Provision the database and its read replicas in Amazon RDS using On-Demand Instances. Store the documents in Amazon EFS. Create a cron job to move the documents that are older than 3 months to Amazon S3 Glacier. Create an AWS Lambda function to delete the documents in S3 Glacier that are older than 7 years.
• D. Create an ECS cluster using a fleet of Spot Instances with Spot Instance draining enabled. Provision the database and its read replicas in Amazon RDS using On-Demand Instances. Store the documents in a secured Amazon S3 bucket with a lifecycle policy to move the documents that are older than 3 months to Amazon S3 Glacier, then delete the documents in Amazon S3 Glacier after 7 years.

Correct answer: B

Explanation

Option B is the most cost-effective solution because using Spot Instances with draining enabled significantly reduces ECS container costs, while Reserved Instances provide the best discount for the continuously running RDS database (since RDS does not support Spot Instances). Additionally, utilizing Amazon S3 lifecycle policies to transition documents to Amazon S3 Glacier and then delete them after 7 years is fully automated and much cheaper than using EBS or EFS. Other options are less cost-effective due to using On-Demand instances or more expensive storage options.