config auto reload flag

main.go

@@ -73,6 +73,7 @@ func main() {
 	flag.StringVar(&opts.LogFormat, "log-format", "console", "Define log format. Allowed values: console, json")
 	flag.BoolVar(&opts.VerifyConfig, "verify-config", false, "Enable this flag to check config file loads, then exit")
 	flag.BoolVar(&opts.Version, "version", false, "set to print version information")
+	flag.BoolVar(&opts.EnableAutoReload, "enable-auto-reload", true, "Enable automatic config reload when the config file changes")
 	flag.Parse()
 
 	if opts.Version {
@@ -126,6 +127,38 @@ func main() {
 		os.Exit(1)
 	}
 
+	var configWatcher *config.ConfigWatcher
+	if opts.EnableAutoReload && opts.ConfigFile != "" {
+		configWatcher, err = config.NewConfigWatcher(logger, opts.ConfigFile, func() {
+			// Create a new config instance for reloading
+			newCfg := config.Config{
+				Listen: config.ListenConfig{
+					Port:            4040,
+					MetricsEndpoint: "/metrics",
+				},
+			}
+
+			if err := config.LoadConfigFromFile(logger, &newCfg, opts.ConfigFile); err != nil {
+				logger.Errorf("error reloading config: %v", err)
+				return
+			}
+
+			if stabilityError := newCfg.StabilityWarnings(); stabilityError != nil && !opts.EnableExperimentalFeatures {
+				logger.Errorf("reloaded config contains experimental features but they are not enabled")
+				return
+			}
+
+			// Update the current config
+			cfg = newCfg
+			logger.Info("configuration reloaded successfully")
+		})
+		if err != nil {
+			logger.Errorf("error setting up config watcher: %v", err)
+		} else {
+			defer configWatcher.Close()
+		}
+	}
+
 	if cfg.Consul.Enable {
 		setupConsul(logger, &cfg, stopChan, &stopHandlers)
 	}

pkg/config/structs.go

@@ -14,6 +14,7 @@ type StartupFlags struct {
 	MetricsEndpoint            string
 	VerifyConfig               bool
 	Version                    bool
+	EnableAutoReload           bool
 
 	LogLevel  string
 	LogFormat string

pkg/config/watcher.go

@@ -0,0 +1,64 @@
+package config
+
+import (
+	"github.com/fsnotify/fsnotify"
+	"github.com/martin-helmich/prometheus-nginxlog-exporter/log"
+)
+
+// ConfigWatcher watches a configuration file for changes
+type ConfigWatcher struct {
+	watcher    *fsnotify.Watcher
+	logger     *log.Logger
+	configFile string
+	onChange   func()
+}
+
+// NewConfigWatcher creates a new configuration watcher
+func NewConfigWatcher(logger *log.Logger, configFile string, onChange func()) (*ConfigWatcher, error) {
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		return nil, err
+	}
+
+	w := &ConfigWatcher{
+		watcher:    watcher,
+		logger:     logger,
+		configFile: configFile,
+		onChange:   onChange,
+	}
+
+	if err := watcher.Add(configFile); err != nil {
+		watcher.Close()
+		return nil, err
+	}
+
+	go w.watch()
+
+	return w, nil
+}
+
+// watch monitors the config file for changes
+func (w *ConfigWatcher) watch() {
+	for {
+		select {
+		case event, ok := <-w.watcher.Events:
+			if !ok {
+				return
+			}
+			if event.Op&fsnotify.Write == fsnotify.Write {
+				w.logger.Infof("config file changed, triggering reload")
+				w.onChange()
+			}
+		case err, ok := <-w.watcher.Errors:
+			if !ok {
+				return
+			}
+			w.logger.Errorf("error watching config file: %v", err)
+		}
+	}
+}
+
+// Close stops watching the configuration file
+func (w *ConfigWatcher) Close() error {
+	return w.watcher.Close()
+}