CloudWatch: Calculate period based on time range

[sunker]

This PR will add logic that will set a period interval based on the time range in case the period field in the query editor is left blank or has the value auto. If the period is actively defined by the user in the query editor, that value will be passed to the GMD api unconditionally. Previously the auto period calculations were made in the frontend, and therefore it didn't work for alerting. This PR moves the period calculation to the backend.

If the period field is not defined by the user, the period will be calculated the following way:
periods = [60, 300, 900, 3600, 21600]
x = timeRangeDeltaInSeconds / 2000
x will then snap to the closest number in the periods array

This is an example with a time range of 30 days
2,592,000 / 2000 = 1296 --> 900 is the closest number

fixes #20652
fixes #18493

[sunker]

@mtanda could you review this, please?

[mtanda]

@sunker Would you add test which confirm the period isn't shorter than CloudWatch retension?

https://aws.amazon.com/about-aws/whats-new/2016/11/cloudwatch-extends-metrics-retention-and-new-user-interface/

Sample test case.

So(closest(periods, (60 * 60 * 24 * 15) + 1), ShouldEqual, 300)
So(closest(periods, (60 * 60 * 24 * 63) + 1), ShouldEqual, 3600)

[marefr]

LGTM

Requested changes fixed

[mtanda]

@sunker When I tested 8616f1b, cloudwatch query is randomly failed.

I get error in my console. Would you test in your environment?

EROR[01-17|22:54:13] Metric request error                     logger=context userId=1 orgId=1 uname=admin error="Error parsing query A, time: invalid duration undefined"

[mtanda]

When I get query error, period is undefined.

When success, the period is empty string.

[mtanda]

I guess it can be reproduced, by creating new panel which use CloudWatch datasource.

[sunker]

Oh, must have been a merge problem. Fix coming right up @mtanda..

[sunker]

@mtanda see #21574

[crxpandion]

I think this commit introduced a behavior where when you zoom in (to say start-end < 15 days) on an event that occurred more than 15 or 63 days prior and period is set to auto the query will use period as 60 resulting in Cloudwatch returning no data.

To fix we will need to have a concept of now in this function to understand which period Cloudwatch has retained.