check if alertmanager being configured is cortex or vanilla (#34726)

public/app/plugins/datasource/alertmanager/ConfigEditor.tsx

@@ -1,5 +1,5 @@
 import { DataSourcePluginOptionsEditorProps } from '@grafana/data';
-import { DataSourceHttpSettings } from '@grafana/ui';
+import { Alert, DataSourceHttpSettings } from '@grafana/ui';
 import React from 'react';
 
 export type Props = DataSourcePluginOptionsEditorProps;
@@ -7,6 +7,9 @@ export type Props = DataSourcePluginOptionsEditorProps;
 export const ConfigEditor: React.FC<Props> = ({ options, onOptionsChange }) => {
   return (
     <>
+      <Alert severity="info" title="Only Cortex alertmanager is supported">
+        Note that only Cortex implementation of alert manager is supported at this time.
+      </Alert>
       <DataSourceHttpSettings
         defaultUrl={''}
         dataSourceConfig={options}

public/app/plugins/datasource/alertmanager/DataSource.ts

@@ -44,12 +44,19 @@ export class AlertManagerDatasource extends DataSourceApi<AlertManagerQuery> {
 
     try {
       alertmanagerResponse = await this._request('/api/v2/status');
+      if (alertmanagerResponse && alertmanagerResponse?.status === 200) {
+        return {
+          status: 'error',
+          message:
+            'Only Cortex alert manager implementation is supported. A URL to cortex instance should be provided.',
+        };
+      }
     } catch (e) {}
     try {
       cortexAlertmanagerResponse = await this._request('/alertmanager/api/v2/status');
     } catch (e) {}
 
-    return alertmanagerResponse?.status === 200 || cortexAlertmanagerResponse?.status === 200
+    return cortexAlertmanagerResponse?.status === 200
       ? {
           status: 'success',
           message: 'Health check passed.',