AWS Certified CloudOps Engineer Associate SOA-C03 Practice Question

An operations team manages an Amazon RDS for MySQL DB instance that occasionally experiences query slow-downs when the CloudWatch metric FreeableMemory falls below 256 MB. The team must be notified by email only if the low-memory condition lasts at least 10 minutes, and they want to keep monitoring costs as low as possible while avoiding false alarms from brief fluctuations. Which CloudWatch alarm configuration meets these requirements?

Create individual low-memory alarms for the instance and any future replicas, then build a composite alarm that evaluates those alarms and publishes to an SNS topic.
Enable Enhanced Monitoring at 1-second granularity and set an alarm on the RDSOSMetrics memoryUsedPercent metric with a 60-second period and evaluation periods set to 10.
Create a high-resolution CloudWatch alarm on FreeableMemory with a 10-second period, evaluation periods set to 60, and an SNS notification action.
Create a standard CloudWatch alarm on the FreeableMemory metric with a 300-second period, evaluation periods set to 2, threshold set to 256 MB, and an alarm action that publishes to an Amazon SNS topic.

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Answer Description

FreeableMemory is a standard Amazon RDS metric that is published to CloudWatch at 1-minute resolution at no additional cost. Setting the alarm period to 300 seconds (5 minutes) and the evaluation periods to 2 ensures the metric must stay below the threshold for a full 10 minutes (2 × 5 minutes) before the alarm enters ALARM state, filtering out short-lived spikes. Publishing the alarm action to an Amazon SNS topic delivers the email notification. High-resolution alarms (10-second periods) and Enhanced Monitoring at 1-second granularity both incur extra charges and are unnecessary for a 10-minute detection window. A composite alarm is also unnecessary for a single DB instance and would add complexity without reducing cost.

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