How to use CloudWatch to monitor an EC2 instance with MySQL installed?

Hello.

I think it is necessary to register data such as the number of active connections to the database in CloudWatch metrics using a shell script or the like.
For example, you can use a shell script to execute the SQL "show status like 'Threads_connected';" and register the value in CloudWatch metrics using "put-metric-data".
https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/PublishMetrics.html#add-metrics-to-scenario

By creating an alarm for the created metrics, it is possible to notify when an abnormality occurs.
https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/ConsoleAlarms.html

If you use RDS instead of EC2, I think most of the metrics you want to see are included in CloudWatch's standard metrics.
In some cases, it may be easier to migrate to RDS.
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/rds-metrics.html