Exams / SAA-C03 / Database cost optimisation / Question 2
SAA-C03 practice question: Database cost optimisation (2 of 2)
Design Cost-Optimized Architectures A free question from our original SAA-C03 practice exam. Try it, then open the answer to see why each option is right or wrong.
A software company runs 10 Amazon RDS for SQL Server Single-AZ DB instances for its development teams. Developers use them only from 08:00 to 18:00 on weekdays, which is 50 of the 168 hours in a week. The project ends in 6 months. The databases and their endpoints must be kept until then, and the team wants as little ongoing effort as possible. Which solution is the MOST cost-effective?
Choose one answer.
- AA. Buy 1-year Reserved Instances for all 10 DB instances, and leave the instances running throughout the week.
- BB. Create Amazon EventBridge Scheduler schedules that stop the DB instances at 18:00 and start them at 08:00 on weekdays.
- CC. Migrate the databases to Aurora Serverless v2 with a minimum capacity of 0 ACUs, so that each one pauses when idle.
- DD. Use an AWS Lambda function to snapshot and delete the instances each evening, and to restore them from the snapshots each morning.
Show the answer and explanation
Answer: B
- A. Wrong: Reserved Instances discount instances that run all the time, but these are needed for only about 30% of the week. A 1-year term also runs 6 months past the end of the project, so the company would keep paying for instances it no longer needs. Learn more: Reserved DB instances for Amazon RDS (opens in a new tab)
- B. Right: Correct. A stopped RDS instance is not charged for instance hours (storage and backups are still charged), keeps its endpoint, and RDS for SQL Server supports stopping Single-AZ instances. Schedules cut about 70% of instance hours with no long-term commitment, and the weekday start means the 7-day automatic restart never comes into play. Learn more: Stopping an Amazon RDS DB instance temporarily (opens in a new tab)
- C. Wrong: Aurora Serverless v2 can scale to 0 ACUs and pause when there are no connections, so it is not billed for capacity while idle. However, Aurora is compatible only with MySQL and PostgreSQL, so SQL Server databases cannot move to it without a full engine migration. Learn more: Scaling to zero ACUs with automatic pause and resume (opens in a new tab)
- D. Wrong: This removes instance charges overnight, but deleting and restoring creates new instances each day, which breaks the requirement to keep the databases and endpoints. Restores also take time every morning and add moving parts to maintain. Stopping and starting the instances gives the saving more simply.
Explanation
The instances are needed for 50 of 168 hours a week, so the biggest saving is to stop paying for the other 118. Stopped RDS instances are not billed for instance hours, keep their endpoints, and are restarted automatically only after 7 days, which a weekday schedule never reaches. The 6-month horizon rules out a 1-year reservation, and the SQL Server engine rules out Aurora Serverless v2.
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