Return reload status from http endpoint (#1152) (#1180)

* Return reload status from http endpoint (#1152)

* Use same reload messaging as prometheus

cmd/alertmanager/main.go

@@ -345,7 +345,7 @@ func main() {
 		router = router.WithPrefix(*routePrefix)
 	}
 
-	webReload := make(chan struct{})
+	webReload := make(chan chan error)
 
 	ui.Register(router, webReload, logger)
 
@@ -367,9 +367,10 @@ func main() {
 		for {
 			select {
 			case <-hup:
-			case <-webReload:
+				reload()
+			case errc := <-webReload:
+				errc <- reload()
 			}
-			reload()
 		}
 	}()
 

ui/web.go

@@ -48,7 +48,7 @@ func serveAsset(w http.ResponseWriter, req *http.Request, fp string, logger log.
 }
 
 // Register registers handlers to serve files for the web interface.
-func Register(r *route.Router, reloadCh chan<- struct{}, logger log.Logger) {
+func Register(r *route.Router, reloadCh chan<- chan error, logger log.Logger) {
 	ihf := prometheus.InstrumentHandlerFunc
 
 	r.Get("/metrics", prometheus.Handler().ServeHTTP)
@@ -73,8 +73,13 @@ func Register(r *route.Router, reloadCh chan<- struct{}, logger log.Logger) {
 	))
 
 	r.Post("/-/reload", func(w http.ResponseWriter, req *http.Request) {
-		w.Write([]byte("Reloading configuration file..."))
-		reloadCh <- struct{}{}
+		errc := make(chan error)
+		defer close(errc)
+
+		reloadCh <- errc
+		if err := <-errc; err != nil {
+			http.Error(w, fmt.Sprintf("failed to reload config: %s", err), http.StatusInternalServerError)
+		}
 	})
 
 	r.Get("/-/healthy", func(w http.ResponseWriter, _ *http.Request) {