The most efficient choice is Deploy the CloudWatch agent to both the on-premises servers and the EC2 instances because this approach collects OS level metrics such as CPU, memory, disk, and network from Linux and Windows hosts and publishes them directly to CloudWatch with a consistent configuration and minimal custom code.

Deploy the CloudWatch agent to both the on-premises servers and the EC2 instances supports a unified configuration for metrics and logs and works across hybrid environments, so you get a single view in CloudWatch without maintaining ad hoc scripts or separate exporters. The agent is managed by AWS and can be configured centrally which reduces operational overhead and improves consistency across the fleet.

Install AWS Distro for OpenTelemetry on all servers and export metrics to CloudWatch is not ideal because the AWS Distro for OpenTelemetry is focused on application telemetry and usually requires more setup to collect host level metrics and to configure exporters, so it is less efficient for simple OS level metric collection.

Enable CloudWatch detailed monitoring for both EC2 instances and on-premises servers is incorrect because detailed monitoring is an EC2 feature and does not apply to on-premises servers, so it cannot provide host metrics from the on-premises portion of the hybrid environment.

Use built-in EC2 metrics in CloudWatch and push on-premises metrics with AWS CLI put-metric-data scripts can work technically but it introduces scripting, maintenance, and operational risk, and it does not provide the consistent, managed collection and configuration that the CloudWatch agent offers.

Full AWS Practitioner Certification Question