How to configure a CloudWatch alarm to evaluate once every X minutes

I would like to configure a CloudWatch alarm to:

• sum the last 30 minutes of the ApplicationRequestsTotal metric once every 30 minutes
• alarm if the sum is equal to 0

I have configured the custom CloudWatch ApplicationRequestsTotal metric to emit once every 60 seconds for my service.

I have configure the alarm as:

{
    "MetricAlarms": [
        {
            "AlarmName": "radio-silence-alarm",
            "AlarmDescription": "Alarm if 0 or less requests are received for 1 consecutive period(s) of 30 minutes.",
            "ActionsEnabled": true,
            "OKActions": [],
            "InsufficientDataActions": [],
            "MetricName": "ApplicationRequestsTotal",
            "Namespace": "AWS/ElasticBeanstalk",
            "Statistic": "Sum",
            "Dimensions": [
                {
                    "Name": "EnvironmentName",
                    "Value": "service-environment"
                }
            ],
            "Period": 1800,
            "EvaluationPeriods": 1,
            "Threshold": 0.0,
            "ComparisonOperator": "LessThanOrEqualToThreshold",
            "TreatMissingData": "missing"
        }
    ],
    "CompositeAlarms": []
}

I have set up many alarms like this and each one seems to:

• sum the last 30 minutes of ApplicationRequestsTotal metric once EVERY minute

For example this service started getting 0 ApplicationRequestsTotal at 8:36a and right at 9:06a CloudWatch triggered an alarm.

The aws cloudwatch describe-alarm-history for the above time period:

{
    "AlarmName": "radio-silence-alarm",
    "AlarmType": "MetricAlarm",
    "Timestamp": "2021-09-29T09:06:37.929000+00:00",
    "HistoryItemType": "StateUpdate",
    "HistorySummary": "Alarm updated from OK to ALARM",
    "HistoryData": "{
       "version":"1.0",
       "oldState":{
          "stateValue":"OK",
          "stateReason":"Threshold Crossed: 1 datapoint [42.0 (22/09/21 08:17:00)] was not less than or equal to the threshold (0.0).",
          "stateReasonData":{
             "version":"1.0",
             "queryDate":"2021-09-22T08:47:37.930+0000",
             "startDate":"2021-09-22T08:17:00.000+0000",
             "statistic":"Sum",
             "period":1800,
             "recentDatapoints":[
                42.0
             ],
             "threshold":0.0,
             "evaluatedDatapoints":[
                {
                   "timestamp":"2021-09-22T08:17:00.000+0000",
                   "sampleCount":30.0,
                   "value":42.0
                }
             ]
          }
       },
       "newState":{
          "stateValue":"ALARM",
          "stateReason":"Threshold Crossed: 1 datapoint [0.0 (29/09/21 08:36:00)] was less than or equal to the threshold (0.0).",
          "stateReasonData":{
             "version":"1.0",
             "queryDate":"2021-09-29T09:06:37.926+0000",
             "startDate":"2021-09-29T08:36:00.000+0000",
             "statistic":"Sum",
             "period":1800,
             "recentDatapoints":[
                0.0
             ],
             "threshold":0.0,
             "evaluatedDatapoints":[
                {
                   "timestamp":"2021-09-29T08:36:00.000+0000",
                   "sampleCount":30.0,
                   "value":0.0
                }
             ]
          }
       }
    }"
}

What have I configured incorrectly?

That is not how Amazon CloudWatch works.

When creating an Alarm in CloudWatch, you specify:

• A metric (eg CPU Utilization, or perhaps a Custom Metric being sent to CloudWatch)
• A time period (eg the previous 30 minutes)
• An aggregation method (eg Average, Sum, Count)

For example, CloudWatch can trigger an Alarm if the Average of the metric was exceeded over the previous 30 minutes. This is continually evaluated as a sliding window. It does not look at metrics in distinct 30-minute blocks.

Using your example, it would send an alert whenever the Sum of the metric is zero for the previous 30 minutes, on a continual basis.