feat(cloudwatch): Support region and account in math expressions

packages/@aws-cdk/aws-cloudwatch/lib/metric-types.ts

@@ -320,6 +320,20 @@ export interface MetricExpressionConfig {
    * How many seconds to aggregate over
    */
   readonly period: number;
+
+  /**
+   * Region which this metric comes from.
+   *
+   * @default Deployment region.
+   */
+  readonly region?: string;
+
+  /**
+   * Account which this metric comes from.
+   *
+   * @default Deployment account.
+   */
+  readonly account?: string;
 }
 
 /**

packages/@aws-cdk/aws-cloudwatch/lib/metric.ts

@@ -133,6 +133,20 @@ export interface MathExpressionOptions {
    * @default Duration.minutes(5)
    */
   readonly period?: cdk.Duration;
+
+  /**
+   * Account which this metric comes from.
+   *
+   * @default - Deployment account.
+   */
+  readonly account?: string;
+
+  /**
+   * Region which this metric comes from.
+   *
+   * @default - Deployment region.
+   */
+  readonly region?: string;
 }
 
 /**
@@ -435,12 +449,20 @@ export class MathExpression implements IMetric {
    */
   public readonly period: cdk.Duration;
 
+  /** Account which this metric comes from */
+  public readonly account?: string;
+
+  /** Region which this metric comes from. */
+  public readonly region?: string;
+
   constructor(props: MathExpressionProps) {
     this.period = props.period || cdk.Duration.minutes(5);
     this.expression = props.expression;
     this.usingMetrics = changeAllPeriods(props.usingMetrics, this.period);
     this.label = props.label;
     this.color = props.color;
+    this.account = props.account;
+    this.region = props.region;
 
     const invalidVariableNames = Object.keys(props.usingMetrics).filter(x => !validVariableName(x));
     if (invalidVariableNames.length > 0) {
@@ -471,6 +493,8 @@ export class MathExpression implements IMetric {
       label: ifUndefined(props.label, this.label),
       color: ifUndefined(props.color, this.color),
       period: ifUndefined(props.period, this.period),
+      account: ifUndefined(props.account, this.account),
+      region: ifUndefined(props.region, this.region),
     });
   }
 
@@ -488,6 +512,8 @@ export class MathExpression implements IMetric {
         period: this.period.toSeconds(),
         expression: this.expression,
         usingMetrics: this.usingMetrics,
+        region: this.region,
+        account: this.account,
       },
       renderingProperties: {
         label: this.label,
@@ -709,4 +735,4 @@ interface IModifiableMetric {
 
 function isModifiableMetric(m: any): m is IModifiableMetric {
   return typeof m === 'object' && m !== null && !!m.with;
-}
+}

packages/@aws-cdk/aws-cloudwatch/lib/private/rendering.ts

@@ -55,6 +55,8 @@ function metricGraphJson(metric: IMetric, yAxis?: string, id?: string) {
 
     withExpression(expr) {
       options.expression = expr.expression;
+      if (expr.account) { options.accountId = accountIfDifferentFromStack(expr.account); }
+      if (expr.region) { options.region = regionIfDifferentFromStack(expr.region); }
     },
   });
 

packages/@aws-cdk/aws-cloudwatch/test/test.metric-math.ts

@@ -93,6 +93,34 @@ export = {
       test.done();
     },
 
+    'MathExpressions can be account and region specific'(test: Test) {
+      // GIVEN
+      const region = 'cn-north-1';
+      const accountA = '1234';
+      const accountB = '5678';
+      const regionalizedMetricA = new Metric({ namespace: 'Test', metricName: 'ACount', region, account: accountA });
+      const regionalizedMetricB = new Metric({ namespace: 'Test', metricName: 'BCount', statistic: 'Average', region, account: accountB });
+      const graph = new GraphWidget({
+        left: [
+          new MathExpression({
+            expression: 'a + b',
+            usingMetrics: { a: regionalizedMetricA, b: regionalizedMetricB },
+            account: accountA,
+            region,
+          }),
+        ],
+      });
+
+      // THEN
+      graphMetricsAre(test, graph, [
+        [ { expression: 'a + b', label: 'a + b', region: 'cn-north-1', accountId: accountA } ],
+        [ 'Test', 'ACount', { visible: false, id: 'a', region: 'cn-north-1', accountId: accountA } ],
+        [ 'Test', 'BCount', { visible: false, id: 'b', region: 'cn-north-1', accountId: accountB } ],
+      ]);
+
+      test.done();
+    },
+
     'can nest MathExpressions in a graph'(test: Test) {
       // GIVEN
       const graph = new GraphWidget({