A company uses memory-optimized Amazon EC2 instances behind a Network Load Balancer (NLB) to run...

EC2 does not publish RAM utilization as a native CloudWatch metric by default. Memory metrics such as mem_used_percent are typically collected by the CloudWatch Agent, which runs on the instance and publishes custom metrics to CloudWatch. Because the requirement is RAM utilization at 5-minute intervals, the CloudWatch Agent can be configured to emit metrics at that cadence (or faster).

“Detailed monitoring” for EC2 mainly affects EC2-provided metrics (like CPU) by changing the period from 5 minutes (basic) to 1 minute (detailed). It does not magically provide memory utilization. Therefore, the key requirement is installing/configuring the CloudWatch Agent and ensuring it has permissions to publish metrics (via an IAM role attached to the instance / instance profile).

Option C correctly combines: (1) basic monitoring (fine for the ask), (2) CloudWatch Agent to publish mem_used_percent, (3) IAM role permissions to allow publishing, and (4) Auto Scaling policy that scales based on the memory metric.

Option B incorrectly implies detailed monitoring provides mem_used_percent (it does not). Option D assumes a “standard” memory metric exists without the agent, which is not correct. Option A references mem_active, which is not the typical metric name exposed by CloudWatch Agent’s standard memory measurements for scaling policies, and also omits the IAM role requirement needed for publishing custom metrics.

Thus, C is the AWS-correct path for memory-based scaling using CloudWatch custom metrics.