A Developer is trying to monitor an application’s status by running a cron job that returns 1 if the service is up and 0 if the service is down. The Developer created code that uses an AWS CLI put-metric-alarm command to publish the custom metrics to Amazon CloudWatch and create an alarm. However, the Developer is unable to create an alarm as the custom metrics do not appear in the CloudWatch console.
What is causing this issue?

A. Sending custom metrics using the CLI is not supported.
B. The Developer needs to use the put-metric-data command.
C. The Developer must use a unified CloudWatch agent to publish custom metrics.
D. The code is not running on an Amazon EC2 instance.