title: AWS Lambda Iterator age alarm is never triggered
body: <p>We have a CloudWatch alarm set for AWS Lambda Itereator age that for some reason is never triggered. Even though the iterator age definitely exceeds the threshold. Here is part of our CloudFormation template that is used for this alarm:</p>
  
  <pre><code>"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"
  </code></pre>