From 34ac5059c1e5d7a02acb9408dafc4491828a2b98 Mon Sep 17 00:00:00 2001
From: Steve Simpson <steve@grafana.com>
Date: Wed, 3 Dec 2025 10:39:54 +0100
Subject: [PATCH] Alerting: Allow missing NGAlert in historian.alerting app
 (#114750)

---
 apps/alerting/historian/pkg/app/app.go        | 26 ++++++++++++-------
 .../apps/alerting/historian/register.go       | 22 +++++++++-------
 2 files changed, 29 insertions(+), 19 deletions(-)

diff --git a/apps/alerting/historian/pkg/app/app.go b/apps/alerting/historian/pkg/app/app.go
index e34e03c9044..2996a21a231 100644
--- a/apps/alerting/historian/pkg/app/app.go
+++ b/apps/alerting/historian/pkg/app/app.go
@@ -16,6 +16,12 @@ import (
 func New(cfg app.Config) (app.App, error) {
 	runtimeConfig := cfg.SpecificConfig.(config.RuntimeConfig)
 
+	alertStateHandler := runtimeConfig.GetAlertStateHistoryHandler
+	if alertStateHandler == nil {
+		alertStateHandler = NewErrorHandler("no alert state handler")
+	}
+	notificationHandler := NewErrorHandler("unimplemented")
+
 	simpleConfig := simple.AppConfig{
 		Name:       "alerting.historian",
 		KubeConfig: cfg.KubeConfig,
@@ -25,12 +31,12 @@ func New(cfg app.Config) (app.App, error) {
 					Namespaced: true,
 					Path:       "/alertstate/history",
 					Method:     "GET",
-				}: runtimeConfig.GetAlertStateHistoryHandler,
+				}: alertStateHandler,
 				{
 					Namespaced: true,
 					Path:       "/notification/query",
 					Method:     "POST",
-				}: UnimplementedHandler,
+				}: notificationHandler,
 			},
 		},
 		// TODO: Remove when SDK is fixed.
@@ -54,12 +60,14 @@ func New(cfg app.Config) (app.App, error) {
 	return a, nil
 }
 
-func UnimplementedHandler(ctx context.Context, writer app.CustomRouteResponseWriter, request *app.CustomRouteRequest) error {
-	return &apierrors.StatusError{
-		ErrStatus: metav1.Status{
-			Status:  metav1.StatusFailure,
-			Code:    http.StatusUnprocessableEntity,
-			Message: "unimplemented",
-		},
+func NewErrorHandler(message string) simple.AppCustomRouteHandler {
+	return func(ctx context.Context, writer app.CustomRouteResponseWriter, request *app.CustomRouteRequest) error {
+		return &apierrors.StatusError{
+			ErrStatus: metav1.Status{
+				Status:  metav1.StatusFailure,
+				Code:    http.StatusUnprocessableEntity,
+				Message: message,
+			},
+		}
 	}
 }
diff --git a/pkg/registry/apps/alerting/historian/register.go b/pkg/registry/apps/alerting/historian/register.go
index fb0e90e7062..78312c326aa 100644
--- a/pkg/registry/apps/alerting/historian/register.go
+++ b/pkg/registry/apps/alerting/historian/register.go
@@ -26,19 +26,21 @@ func RegisterAppInstaller(
 	cfg *setting.Cfg,
 	ng *ngalert.AlertNG,
 ) (*AlertingHistorianAppInstaller, error) {
-	if ng.IsDisabled() {
-		log.New("app-registry").Info("Skipping Kubernetes Alerting Historian apiserver (historian.alerting.grafana.app): Unified Alerting is disabled")
-		return nil, nil
-	}
-
 	installer := &AlertingHistorianAppInstaller{}
+	appSpecificConfig := historianAppConfig.RuntimeConfig{}
 
-	handlers := &handlers{
-		historian: ng.Api.Historian,
-	}
+	// If we're provided an AlertNG, then call back into that for things we need.
+	// This is a temporary whilst building out the app; we should not depend on it.
+	if ng != nil {
+		if ng.IsDisabled() {
+			log.New("app-registry").Info("Skipping Kubernetes Alerting Historian apiserver (historian.alerting.grafana.app): Unified Alerting is disabled")
+			return nil, nil
+		}
 
-	appSpecificConfig := historianAppConfig.RuntimeConfig{
-		GetAlertStateHistoryHandler: handlers.GetAlertStateHistoryHandler,
+		handlers := &handlers{
+			historian: ng.Api.Historian,
+		}
+		appSpecificConfig.GetAlertStateHistoryHandler = handlers.GetAlertStateHistoryHandler
 	}
 
 	provider := simple.NewAppProvider(apis.LocalManifest(), appSpecificConfig, historianApp.New)