(cloudwatch): Allow cross-region alarms

[Kyle-Thompson]

I would like to be able to define alarms in one monitoring account to trigger based off of metrics from other accounts. It seems currently possible to create graphs from metrics from different accounts but not alarms.

Consider the following, functional piece of code:

        let avgMetrics = new Map();
        Object.keys(offsetDashboardNames).map((offset:string) => {
            avgMetrics.set(offset, new cloudwatch.MathExpression({
                expression: 'AVG([m1,m2,m3,m4,m5,m6,m7])',
                period: cdk.Duration.days(1),
                usingMetrics: {
                    "m1": offsetMetrics.get(offset)!.get(Regions[0])!,
                    "m2": offsetMetrics.get(offset)!.get(Regions[1])!,
                    "m3": offsetMetrics.get(offset)!.get(Regions[2])!,
                    "m4": offsetMetrics.get(offset)!.get(Regions[3])!,
                    "m5": offsetMetrics.get(offset)!.get(Regions[4])!,
                    "m6": offsetMetrics.get(offset)!.get(Regions[5])!,
                    "m7": offsetMetrics.get(offset)!.get(Regions[6])!,
                },
                color: '#000000',
                label: 'Aggregate'
            }))
        })

where Regions[i] represents an account id. This works but not when I try to add an alarm to trigger on any of these metrics falling below a threshold as shown here:

        let secondDay = offsetMetrics.get("-2")!;
        let alarm = new cloudwatch.MathExpression({
            expression: 'MIN([m1,m2,m3,m4,m5,m6,m7])',
            period: cdk.Duration.days(1),
            usingMetrics: {
                "m1": secondDay.get(Regions[0])!,
                "m2": secondDay.get(Regions[1])!,
                "m3": secondDay.get(Regions[2])!,
                "m4": secondDay.get(Regions[3])!,
                "m5": secondDay.get(Regions[4])!,
                "m6": secondDay.get(Regions[5])!,
                "m7": secondDay.get(Regions[6])!
            },
            color: '#000000',
            label: 'Aggregate'
        }).createAlarm(this, "DataAvailabilityAlarm", {
            evaluationPeriods: 1,
            threshold: 0.75,
            alarmDescription: "Do we have data from 2 days ago?",
            alarmName: "SufficientDataIngested",
            comparisonOperator: cloudwatch.ComparisonOperator.LESS_THAN_THRESHOLD,
            datapointsToAlarm: 1,
            treatMissingData: cloudwatch.TreatMissingData.MISSING
        })

I end up getting this error:

Using cdk out from cdk.json: /local/home/thoakyl/workplace/fix_alarm/src/AwsApiMetricsWorkerDashboardsCDK/build/cdk.out
/local/home/thoakyl/workplace/fix_alarm/src/AwsApiMetricsWorkerDashboardsCDK/node_modules/monocdk/lib/aws-cloudwatch/lib/alarm.js:263
            throw new Error(`Cannot create an Alarm in region '${stack.region}' based on metric '${metric}' in '${stat.region}'`);
            ^

Error: Cannot create an Alarm in region 'us-east-1' based on metric 'AvailabilityRate' in 'ap-northeast-1'
    at Alarm.validateMetricStat (/local/home/thoakyl/workplace/fix_alarm/src/AwsApiMetricsWorkerDashboardsCDK/node_modules/monocdk/lib/aws-cloudwatch/lib/alarm.js:263:19)
    at Object.withStat (/local/home/thoakyl/workplace/fix_alarm/src/AwsApiMetricsWorkerDashboardsCDK/node_modules/monocdk/lib/aws-cloudwatch/lib/alarm.js:221:34)
    at Object.dispatchMetric (/local/home/thoakyl/workplace/fix_alarm/src/AwsApiMetricsWorkerDashboardsCDK/node_modules/monocdk/lib/aws-cloudwatch/lib/private/metric-util.js:115:20)
    at /local/home/thoakyl/workplace/fix_alarm/src/AwsApiMetricsWorkerDashboardsCDK/node_modules/monocdk/lib/aws-cloudwatch/lib/alarm.js:218:70
    at Array.map (<anonymous>)
    at Object.withExpression (/local/home/thoakyl/workplace/fix_alarm/src/AwsApiMetricsWorkerDashboardsCDK/node_modules/monocdk/lib/aws-cloudwatch/lib/alarm.js:218:43)
    at Object.dispatchMetric (/local/home/thoakyl/workplace/fix_alarm/src/AwsApiMetricsWorkerDashboardsCDK/node_modules/monocdk/lib/aws-cloudwatch/lib/private/metric-util.js:118:20)
    at Alarm.renderMetric (/local/home/thoakyl/workplace/fix_alarm/src/AwsApiMetricsWorkerDashboardsCDK/node_modules/monocdk/lib/aws-cloudwatch/lib/alarm.js:174:30)
    at new Alarm (/local/home/thoakyl/workplace/fix_alarm/src/AwsApiMetricsWorkerDashboardsCDK/node_modules/monocdk/lib/aws-cloudwatch/lib/alarm.js:63:34)
    at MathExpression.createAlarm (/local/home/thoakyl/workplace/fix_alarm/src/AwsApiMetricsWorkerDashboardsCDK/node_modules/monocdk/lib/aws-cloudwatch/lib/metric.js:371:16)

It seems odd that I'd be able to create graphs with metrics from other accounts but not alarms based on them.

Proposed Solution

At the moment I'm not aware of how this functionality could be implemented but I'm happy to get a workaround in the meantime.

[kaizencc]

Hi! According to the cloudwatch docs, you can create cross-account alarms but not cross-region ones. Cross-region seems to be only supported by graphs and dashboards at the moment.

With the CDK, you can create an alarm that monitors metrics in different accounts but the same region. Hope that helps!

[github-actions]

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