From d3cd4017345994cd8cef589379e9b872cfe63947 Mon Sep 17 00:00:00 2001
From: Ashley Harrison <ashley.harrison@grafana.com>
Date: Wed, 15 Oct 2025 13:35:24 +0100
Subject: [PATCH] Frontend service: Add `/-/fe-boot-error` endpoint to track
 errors starting the frontend service (#112375)

* add /-/fe-boot-error endpoint to track errors starting the frontend service

* use promauto package

* move metric to root

* check error of r.Body.Close()
---
 pkg/services/frontend/frontend_service.go | 47 +++++++++++++++++++++++
 pkg/services/frontend/index.html          | 17 +++++++-
 2 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/pkg/services/frontend/frontend_service.go b/pkg/services/frontend/frontend_service.go
index 32cea9cffc8..d1e343dede7 100644
--- a/pkg/services/frontend/frontend_service.go
+++ b/pkg/services/frontend/frontend_service.go
@@ -2,11 +2,13 @@ package frontend
 
 import (
 	"context"
+	"io"
 	"net"
 	"net/http"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/trace"
@@ -25,6 +27,14 @@ import (
 
 var tracer = otel.Tracer("github.com/grafana/grafana/pkg/services/frontend")
 
+// Initialize metrics
+var bootErrorMetric = promauto.NewCounter(prometheus.CounterOpts{
+	Namespace: "grafana",
+	Subsystem: "frontend",
+	Name:      "boot_errors_total",
+	Help:      "Total number of frontend boot errors",
+})
+
 type frontendService struct {
 	*services.BasicService
 	cfg          *setting.Cfg
@@ -117,6 +127,11 @@ func (s *frontendService) routeGet(m *web.Mux, pattern string, h ...web.Handler)
 	m.Get(pattern, handlers...)
 }
 
+func (s *frontendService) routePost(m *web.Mux, pattern string, h ...web.Handler) {
+	handlers := append([]web.Handler{middleware.ProvideRouteOperationName(pattern)}, h...)
+	m.Post(pattern, handlers...)
+}
+
 // Apply the same middleware patterns as the main HTTP server
 func (s *frontendService) addMiddlewares(m *web.Mux) {
 	loggermiddleware := loggermw.Provide(s.cfg, s.features)
@@ -148,6 +163,38 @@ func (s *frontendService) registerRoutes(m *web.Mux) {
 		}
 	})
 
+	// Frontend boot error reporting endpoint
+	s.routePost(m, "/-/fe-boot-error", s.handleBootError)
+
 	// All other requests return index.html
 	s.routeGet(m, "/*", s.index.HandleRequest)
 }
+
+// handleBootError handles frontend boot error reports
+func (s *frontendService) handleBootError(w http.ResponseWriter, r *http.Request) {
+	// Read the request body
+	body, err := io.ReadAll(r.Body)
+	if err != nil {
+		s.log.Error("failed to read boot error request body", "error", err)
+		http.Error(w, "Bad request", http.StatusBadRequest)
+		return
+	}
+
+	defer func() {
+		if err := r.Body.Close(); err != nil {
+			s.log.Warn("Failed to close response body", "err", err)
+		}
+	}()
+
+	// Increment the Prometheus counter
+	bootErrorMetric.Inc()
+
+	// Log the error details
+	s.log.Error("frontend boot error reported", "error", body)
+
+	// Return success response
+	w.WriteHeader(http.StatusOK)
+	if _, err := w.Write([]byte("OK")); err != nil {
+		s.log.Error("failed to write boot error response", "error", err)
+	}
+}
diff --git a/pkg/services/frontend/index.html b/pkg/services/frontend/index.html
index 957581dc56f..34c4d4f89ed 100644
--- a/pkg/services/frontend/index.html
+++ b/pkg/services/frontend/index.html
@@ -169,10 +169,23 @@
       // Wrap in an IIFE to avoid polluting the global scope. Intentionally global-scope properties
       // are explicitly assigned to the `window` object.
       (() => {
-        window.__grafana_load_failed = function(...args) {
-          console.error('Failed to load Grafana', ...args);
+        window.__grafana_load_failed = function(err) {
+          console.error('Failed to load Grafana', err);
           document.querySelector('.fs-variant-loader').classList.add('fs-hidden');
           document.querySelector('.fs-variant-error').classList.remove('fs-hidden');
+
+          // Report the error to the backend
+          const errorMessage = err ? err.message : 'Unknown error';
+
+          fetch('/-/fe-boot-error', {
+            method: 'POST',
+            headers: {
+              'Content-Type': 'application/json',
+            },
+            body: errorMessage,
+          }).catch(err => {
+            console.error('Failed to report boot error to backend: ', err);
+          });
         };
 
         window.onload = function() {