Which systems resource requires using a custom metric for CloudWatch Monitoring?

Memory Usage requires using a custom metric for CloudWatch Monitoring because, by default, Amazon CloudWatch does not provide built-in metrics for memory utilization on EC2 instances or other resources. While metrics like CPU Utilization, Network Inbound, and Disk Writes are automatically tracked and reported by CloudWatch, memory usage is not included among the standard metrics.

To monitor memory usage, you must create a custom CloudWatch metric that collects and reports the data. This typically involves using scripts on the instance that gather memory statistics and send them to CloudWatch, allowing administrators to gain insights into how memory is being utilized and to set alarms or notifications for scenarios like low memory availability. This approach enables better optimization and troubleshooting of applications running in the cloud.