Exit early on invalid config file (#7399)

* Reload config file at start

Signed-off-by: Harkishen-Singh <harkishensingh@hotmail.com>

* relocated config checking

Signed-off-by: Harkishen-Singh <harkishensingh@hotmail.com>

* change log lever

Signed-off-by: Harkishen-Singh <harkishensingh@hotmail.com>

* add helpful comment

Signed-off-by: Harkishen-Singh <harkishensingh@hotmail.com>

cmd/prometheus/main.go

@@ -278,6 +278,12 @@ func main() {
 		os.Exit(2)
 	}
 
+	// Throw error for invalid config before starting other components.
+	if _, err := config.LoadFile(cfg.configFile); err != nil {
+		level.Error(logger).Log("msg", fmt.Sprintf("Error loading config (--config.file=%s)", cfg.configFile), "err", err)
+		os.Exit(2)
+	}
+
 	cfg.web.ReadTimeout = time.Duration(cfg.webTimeout)
 	// Default -web.route-prefix to path of -web.external-url.
 	if cfg.web.RoutePrefix == "" {

cmd/prometheus/main_test.go

@@ -111,7 +111,7 @@ func TestFailedStartupExitCode(t *testing.T) {
 	}
 
 	fakeInputFile := "fake-input-file"
-	expectedExitStatus := 1
+	expectedExitStatus := 2
 
 	prom := exec.Command(promPath, "-test.main", "--config.file="+fakeInputFile)
 	err := prom.Run()