[aws-cloudwatch] The period of a MathExpression is not respected on CloudWatch

[jrmcornish]

The period of a MathExpression CloudWatch metric that is used in a GraphWidget is currently not respected. In particular, it is possible to specify a period of 1 minute, but for data points still to be spaced every 5 minutes.

Reproduction Steps

Assume below that queue is some aws_sqs.Queue, and dashboard is some aws_cloudwatch.Dashboard. Then consider the following:

metric = queue.metric_approximate_number_of_messages_visible()

dashboard.add_widgets(
    aws_cloudwatch.GraphWidget(
        left=[
            aws_cloudwatch.MathExpression(
                expression=f"2 * x",
                using_metrics={"x": metric},
                period=core.Duration.minutes(1)
            )
        ]
    )
)

In CloudWatch, this produces a widget showing data points every 5 minutes, rather than every 1 minute as expected.

Error Log

The actual JSON produced for the widget above will be similar to the following (apart from QueueName and region changes):

{
    "view": "timeSeries",
    "region": "us-east-1",
    "metrics": [
        [ { "label": "2 * x", "expression": "2 * x", "region": "us-east-1" } ],
        [ "AWS/SQS", "ApproximateNumberOfMessagesVisible", "QueueName", "MY_QUEUE_NAME", { "period": 60, "stat": "Maximum", "visible": false, "id": "x" } ]
    ],
    "period": 300
}

This corresponds to showing measurements spaced every 5 minutes by default.

If the first metrics item in the dictionary above is replaced with

        [ { "label": "2 * x", "expression": "2 * x", "region": "us-east-1", "period": 60 } ],

then data points are spaced correctly every 1 minute. However, the code produced by the CDK does not generate this.

Environment

• CLI Version : aws-cli/1.18.8 Python/3.7.4 Linux/5.3.0-62-generic botocore/1.15.8
• Framework Version: 1.45.0 (build 0cfab15)
• Node.js Version: v10.16.3
• OS : Linux 5.3.0-62-generic #56~18.04.1-Ubuntu SMP Wed Jun 24 16:17:03 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
• Language (Version): Python 3.7.4

Other

---

This is 🐛 Bug Report

[rix0rrr]

Well we completely generated it like this on purpose, where the math expression would get rendered at the resolution of the underlying metrics. I remember testing this, and I wonder if CloudWatch changed its behavior here.

The fix is probably to always emit a period for the math expression.

[github-actions]

⚠️COMMENT VISIBILITY WARNING⚠️

Comments on closed issues are hard for our team to see.
If you need more assistance, please either tag a team member or open a new issue that references this one.
If you wish to keep having a conversation with other community members under this issue feel free to do so.