add "verify-config" flag that load and verify configuration and exits…

… with proper exit code (grafana#2737)

Signed-off-by: Cyril Tovena <cyril.tovena@gmail.com>

cmd/loki/main.go

@@ -33,13 +33,15 @@ var lineReplacer = strings.NewReplacer("\n", "\\n  ")
 type Config struct {
 	loki.Config  `yaml:",inline"`
 	printVersion bool
+	verifyConfig bool
 	printConfig  bool
 	logConfig    bool
 	configFile   string
 }
 
 func (c *Config) RegisterFlags(f *flag.FlagSet) {
 	f.BoolVar(&c.printVersion, "version", false, "Print this builds version information")
+	f.BoolVar(&c.verifyConfig, "verify-config", false, "Verify config file and exits")
 	f.BoolVar(&c.printConfig, "print-config-stderr", false, "Dump the entire Loki config object to stderr")
 	f.BoolVar(&c.logConfig, "log-config-reverse-order", false, "Dump the entire Loki config object at Info log "+
 		"level with the order reversed, reversing the order makes viewing the entries easier in Grafana.")
@@ -87,6 +89,11 @@ func main() {
 		os.Exit(1)
 	}
 
+	if config.verifyConfig {
+		level.Info(util.Logger).Log("msg", "config is valid")
+		os.Exit(0)
+	}
+
 	if config.printConfig {
 		err := logutil.PrintConfig(os.Stderr, &config)
 		if err != nil {