async function createMissingAlarms()

in workmail-stop-mail-storm/src/app.js [36:78]
30 lines of code
3 McCabe index (conditional complexity)

async function createMissingAlarms(alarms, protectedRecipients) {
    // find the protected addresses for which there is already an alarm
    const protectedAddressesWithAlarm = alarms.MetricAlarms
        .map(metricAlarm => metricAlarm.Dimensions[0].Value);

    // remove those from all alarms. the remaining addresses are missing alarms
    const protectedAddressesMissingAlarm = protectedRecipients
        .filter(protectedAddress => !protectedAddressesWithAlarm.includes(protectedAddress));

    // create the alarm for those
    for (let protectedAddress of protectedAddressesMissingAlarm) {
        // this will create an alarm that will fire if we receive in 3 different minutes more than THRESHOLD emails
        // per minute, in a window of the last 5 minutes.

        // see https://docs.aws.amazon.com/AmazonCloudWatch/latest/APIReference/API_PutMetricAlarm.html for detailed
        // explanation of the parameters
        const params = {
            AlarmName: ALARM_PREFIX + protectedAddress,
            ComparisonOperator: 'GreaterThanThreshold',
            AlarmDescription: 'Mail storm in progress for group ' + protectedAddress,
            Dimensions: [
                {
                    Name: 'EmailAddress',
                    Value: protectedAddress
                },
            ],
            MetricName: 'EmailsReceived',
            Namespace: 'WorkMail',
            TreatMissingData: 'notBreaching',
            // The parameters below control how sensitive the detection for mailstorm is.
            DatapointsToAlarm: 3, // alarm if 3 of the last 5 datapoints are above threshold
            EvaluationPeriods: 5,
            Period: 60, // each data point for evaluation is a sum of emails received in the last 60 s.
            Statistic: 'Sum',
            // configure using the THRESHOLD lambda environment variable
            Threshold: parseInt(process.env.THRESHOLD || DEFAULT_THRESHOLD),

        };
        console.log('Creating alarm for address ' + protectedAddress);
        const alarm = await cloudwatch.putMetricAlarm(params).promise();
        console.log(alarm);
    }
}