[Metrics UI] Add back context variables with descriptions

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

@@ -336,6 +336,9 @@ export const createMetricThresholdExecutor = (libs: InfraBackendLibs, alertId: s
           group,
           alertState: stateToAlertMessage[nextState],
           reason,
+          value: mapToConditionsLookup(alertResults, (result) => result[group].currentValue),
+          threshold: mapToConditionsLookup(criteria, (c) => c.threshold),
+          metric: mapToConditionsLookup(criteria, (c) => c.metric),
         });
       }
 
@@ -352,3 +355,14 @@ export const FIRED_ACTIONS = {
     defaultMessage: 'Fired',
   }),
 };
+
+const mapToConditionsLookup = (
+  list: any[],
+  mapFn: (value: any, index: number, array: any[]) => unknown
+) =>
+  list
+    .map(mapFn)
+    .reduce(
+      (result: Record<string, any>, value, i) => ({ ...result, [`condition${i}`]: value }),
+      {}
+    );

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

@@ -55,6 +55,30 @@ export function registerMetricThresholdAlertType(libs: InfraBackendLibs) {
     }
   );
 
+  const valueActionVariableDescription = i18n.translate(
+    'xpack.infra.metrics.alerting.threshold.alerting.valueActionVariableDescription',
+    {
+      defaultMessage:
+        'The value of the metric in the specified condition. Usage: (ctx.value.condition0, ctx.value.condition1, etc...).',
+    }
+  );
+
+  const metricActionVariableDescription = i18n.translate(
+    'xpack.infra.metrics.alerting.threshold.alerting.metricActionVariableDescription',
+    {
+      defaultMessage:
+        'The metric name in the specified condition. Usage: (ctx.metric.condition0, ctx.metric.condition1, etc...).',
+    }
+  );
+
+  const thresholdActionVariableDescription = i18n.translate(
+    'xpack.infra.metrics.alerting.threshold.alerting.thresholdActionVariableDescription',
+    {
+      defaultMessage:
+        'The threshold value of the metric for the specified condition. Usage: (ctx.threshold.condition0, ctx.threshold.condition1, etc...).',
+    }
+  );
+
   return {
     id: METRIC_THRESHOLD_ALERT_TYPE_ID,
     name: 'Metric threshold',
@@ -82,6 +106,9 @@ export function registerMetricThresholdAlertType(libs: InfraBackendLibs) {
         { name: 'group', description: groupActionVariableDescription },
         { name: 'alertState', description: alertStateActionVariableDescription },
         { name: 'reason', description: reasonActionVariableDescription },
+        { name: 'value', description: valueActionVariableDescription },
+        { name: 'metric', description: metricActionVariableDescription },
+        { name: 'threshold', description: thresholdActionVariableDescription },
       ],
     },
     producer: 'metrics',