Pass a reason to the alert instance factory

x-pack/plugins/infra/server/lib/alerting/inventory_metric_threshold/inventory_metric_threshold_executor.ts

@@ -7,6 +7,7 @@
 
 import { first, get, last } from 'lodash';
 import { i18n } from '@kbn/i18n';
+import { ALERT_REASON } from '@kbn/rule-data-utils';
 import moment from 'moment';
 import { getCustomMetricLabel } from '../../../../common/formatters/get_custom_metric_label';
 import { toMetricOpt } from '../../../../common/snapshot_metric_i18n';
@@ -56,6 +57,7 @@ type InventoryMetricThresholdAlertInstance = AlertInstance<
 >;
 type InventoryMetricThresholdAlertInstanceFactory = (
   id: string,
+  reason: string,
   threshold?: number | undefined,
   value?: number | undefined
 ) => InventoryMetricThresholdAlertInstance;
@@ -77,10 +79,12 @@ export const createInventoryMetricThresholdExecutor = (libs: InfraBackendLibs) =
     } = params as InventoryMetricThresholdParams;
     if (criteria.length === 0) throw new Error('Cannot execute an alert with 0 conditions');
     const { alertWithLifecycle, savedObjectsClient } = services;
-    const alertInstanceFactory: InventoryMetricThresholdAlertInstanceFactory = (id) =>
+    const alertInstanceFactory: InventoryMetricThresholdAlertInstanceFactory = (id, reason) =>
       alertWithLifecycle({
         id,
-        fields: {},
+        fields: {
+          [ALERT_REASON]: reason,
+        },
       });
 
     const source = await libs.sources.getSourceConfiguration(
@@ -175,7 +179,7 @@ export const createInventoryMetricThresholdExecutor = (libs: InfraBackendLibs) =
             ? WARNING_ACTIONS.id
             : FIRED_ACTIONS.id;
 
-        const alertInstance = alertInstanceFactory(`${item}`);
+        const alertInstance = alertInstanceFactory(`${item}`, reason);
         alertInstance.scheduleActions(
           /**
            * TODO: We're lying to the compiler here as explicitly  calling `scheduleActions` on