[Metrics UI] Fix evaluating rate-aggregated alerts when there's no normalized value (#73545)

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

x-pack/plugins/infra/server/lib/alerting/metric_threshold/lib/evaluate_alert.ts

@@ -67,10 +67,13 @@ export const evaluateAlert = (
           currentValue: Array.isArray(points) ? last(points)?.value : NaN,
           timestamp: Array.isArray(points) ? last(points)?.key : NaN,
           shouldFire: Array.isArray(points)
-            ? points.map((point) => comparisonFunction(point.value, threshold))
+            ? points.map(
+                (point) =>
+                  typeof point.value === 'number' && comparisonFunction(point.value, threshold)
+              )
             : [false],
-          isNoData: points === null,
-          isError: isNaN(points),
+          isNoData: (Array.isArray(points) ? last(points)?.value : points) === null,
+          isError: isNaN(Array.isArray(points) ? last(points)?.value : points),
         };
       });
     })
@@ -172,7 +175,7 @@ const getValuesFromAggregations = (
     }
     return buckets.map((bucket) => ({
       key: bucket.key_as_string,
-      value: bucket.aggregatedValue.value,
+      value: bucket.aggregatedValue?.value ?? null,
     }));
   } catch (e) {
     return NaN; // Error state

x-pack/plugins/infra/server/lib/alerting/metric_threshold/metric_threshold_executor.test.ts

@@ -318,6 +318,31 @@ describe('The metric threshold alert type', () => {
     });
   });
 
+  describe("querying a rate-aggregated metric that hasn't reported data", () => {
+    const instanceID = '*';
+    const execute = () =>
+      executor({
+        services,
+        params: {
+          criteria: [
+            {
+              ...baseCriterion,
+              comparator: Comparator.GT,
+              threshold: 1,
+              metric: 'test.metric.3',
+              aggType: 'rate',
+            },
+          ],
+          alertOnNoData: true,
+        },
+      });
+    test('sends a No Data alert', async () => {
+      await execute();
+      expect(mostRecentAction(instanceID).id).toBe(FIRED_ACTIONS.id);
+      expect(getState(instanceID).alertState).toBe(AlertStates.NO_DATA);
+    });
+  });
+
   // describe('querying a metric that later recovers', () => {
   //   const instanceID = '*';
   //   const execute = (threshold: number[]) =>
@@ -401,7 +426,9 @@ services.callCluster.mockImplementation(async (_: string, { body, index }: any)
   if (metric === 'test.metric.2') {
     return mocks.alternateMetricResponse;
   } else if (metric === 'test.metric.3') {
-    return mocks.emptyMetricResponse;
+    return body.aggs.aggregatedIntervals.aggregations.aggregatedValue_max
+      ? mocks.emptyRateResponse
+      : mocks.emptyMetricResponse;
   }
   return mocks.basicMetricResponse;
 });

x-pack/plugins/infra/server/lib/alerting/metric_threshold/test_mocks.ts

@@ -62,6 +62,19 @@ export const emptyMetricResponse = {
   },
 };
 
+export const emptyRateResponse = {
+  aggregations: {
+    aggregatedIntervals: {
+      buckets: [
+        {
+          doc_count: 2,
+          aggregatedValue_max: { value: null },
+        },
+      ],
+    },
+  },
+};
+
 export const basicCompositeResponse = {
   aggregations: {
     groupings: {