永远不会触发AWS Lambda Iterator年龄警报

Question

我们为AWS Lambda Itereator年龄设置了CloudWatch警报，出于某种原因，该警报从未触发。即使迭代器的年龄肯定超过了阈值。这是用于此警报的CloudFormation模板的一部分：

"TreatMissingData": "missing",
"ComparisonOperator": "GreaterThanOrEqualToThreshold",
"Dimensions": [{
    "Name": "FunctionName",
    "Value": {
        "Ref": "LambdaFunction"
    }
}],
"EvaluationPeriods": 1,
"InsufficientDataActions": [],
"MetricName": "IteratorAge",
"Namespace": "AWS/Lambda",
"OKActions": [{
    "Ref": "NotificationTopic"
}],
"Period": 900,
"Statistic": "Minimum",
"Threshold": 1800000,
"Unit": "Microseconds"