Hi, You cannot delete a metric from CloudWatch, you stop emitting it. That means that
- if you don't need the metric anymore, you dismiss the resource or stop calling the API, the metric will not receive any new data. It will still appear during 2 weeks, and then disappear
- if you still need the metric but under a different name/namespace, you update the name in your API/agent config, and you will see the metric under both names for 14 days: it will still appear under the old name with past data, and under the new name with new data, until 2 weeks after you made the change. At that time, CloudWatch will stop showing the old name as it won't have received new data for that old name for a continued period of 2 weeks, and only the new name will remain visible in the console from then on
Sorry I'm not sure I understand what you mean with the alarm not triggering. Alarms do not disappear automatically, they keep on evaluating. If you stop emitting a metric or rename it, you should update your alarm's definition (or delete the alarm if you don't need it anymore).
to question 1, the answer is yes, the only way to change the alarm name is to delete it and recreate it.
To question 2, you don't "delete" the metrics from CloudWatch, you stop sending them. They will still appear for 2 weeks in your console (support pages state "A metric is available in the CloudWatch console only if a data point was pushed to the metric in the last 14 days"). After that, they should automatically stop showing in your console.
If you have an alarm based on a metric that should never occur, the alarm will be in an 'insufficient data' state until it receives something. Under additional configuration, you can set the missing data treatment behaviour on the alarm for it to be 'good' if you want to keep it in an OK state when data hasn't been received.
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