metricFactory.createMetricSearch doesn't support empty dimension map

[jakeinater]

Feature scope

MetricFactory

Describe your suggested feature

Declaring CustomMetricGroup as following:

      {
        title: 'Test',
        metrics: [
          metricFactory.createMetricSearch(
            'query',
            { dummyDim: undefined as any as string },
            MetricStatistic.SUM,
          ) as MathExpression,
        ],
      },

Which generates a graph with following search query:

SEARCH('{test_namespace,dummyDim}  EligibleEvent', 'Sum', 60)

As far as I can tell, there is no way to omit the DimensionMap. When I emit the metric, I don't associate any dimension, so I need to associate a dummy dimension, which is a little hacky.

Nit: Also unrelated issue, createMetricSearch returns IMetric, which is incompatible with what the MonitoringFacade expects (Metric | MathExpression) resulting in me needing to cast the return into a MathExpression.

Related code snippet:

cdk-monitoring-constructs/lib/common/metric/MetricFactory.ts

Lines 148 to 185 in e7aa66b

	createMetricSearch(
	query: string,
	dimensionsMap: DimensionsMap,
	statistic: MetricStatistic,
	namespace?: string,
	label?: string,
	period?: Duration,
	region?: string,
	account?: string
	): IMetric {
	const finalPeriod =
	period ?? this.globalDefaults.period ?? DefaultMetricPeriod;
	const searchNamespace = this.getNamespaceWithFallback(namespace);
	const namespacePlusDimensionKeys = [
	searchNamespace,
	...Object.keys(dimensionsMap),
	].join(",");
	const metricSchema = `{${namespacePlusDimensionKeys}}`;
	const dimensionKeysAndValues = Object.entries(
	this.removeUndefinedEntries(dimensionsMap)
	)
	.map(([key, value]) => `${key}="${value}"`)
	.join(" ");
	const expression = `SEARCH('${metricSchema} ${dimensionKeysAndValues} ${query}', '${statistic}', ${finalPeriod.toSeconds()})`;
	return new MathExpression({
	expression,
	// see https://github.com/aws/aws-cdk/issues/7237
	usingMetrics: {},
	// cannot be an empty string and undefined is no good either
	label: label ?? " ",
	period: finalPeriod,
	searchRegion: region ?? this.globalDefaults.region,
	searchAccount: account ?? this.globalDefaults.account,
	});
	}