feat(agent): Add debounce for watch events

cmd/telegraf/main.go

@@ -231,6 +231,7 @@ func runApp(args []string, outputBuffer io.Writer, pprof Server, c TelegrafConfi
 			configURLWatchInterval:  cCtx.Duration("config-url-watch-interval"),
 			watchConfig:             cCtx.String("watch-config"),
 			watchInterval:           cCtx.Duration("watch-interval"),
+			watchDebounceInterval:   cCtx.Duration("watch-debounce-interval"),
 			pidFile:                 cCtx.String("pidfile"),
 			plugindDir:              cCtx.String("plugin-directory"),
 			password:                cCtx.String("password"),
@@ -295,6 +296,12 @@ func runApp(args []string, outputBuffer io.Writer, pprof Server, c TelegrafConfi
 					Usage: "monitoring config changes [notify, poll] of --config and --config-directory options. " +
 						"Notify supports linux, *bsd, and macOS. Poll is required for Windows and checks every 250ms.",
 				},
+				&cli.DurationFlag{
+					Name:        "watch-debounce-interval",
+					Usage:       "Time duration to wait after a config change before reloading",
+					DefaultText: "0s",
+					Value:       0,
+				},
 				&cli.StringFlag{
 					Name:  "pidfile",
 					Usage: "file to write our pid to",

cmd/telegraf/telegraf.go

@@ -41,6 +41,7 @@ type GlobalFlags struct {
 	configURLWatchInterval  time.Duration
 	watchConfig             string
 	watchInterval           time.Duration
+	watchDebounceInterval   time.Duration
 	pidFile                 string
 	plugindDir              string
 	password                string
@@ -231,30 +232,104 @@ func (t *Telegraf) watchLocalConfig(ctx context.Context, signals chan os.Signal,
 		return
 	}
 	log.Printf("I! Config watcher started for %s\n", fConfig)
-	select {
-	case <-ctx.Done():
-		mytomb.Done()
-		return
-	case <-changes.Modified:
-		log.Printf("I! Config file/directory %q modified\n", fConfig)
-	case <-changes.Deleted:
-		// deleted can mean moved. wait a bit a check existence
-		<-time.After(time.Second)
-		if _, err := os.Stat(fConfig); err == nil {
-			log.Printf("I! Config file/directory %q overwritten\n", fConfig)
-		} else {
-			log.Printf("W! Config file/directory %q deleted\n", fConfig)
+
+	// Setup debounce timer
+	var reloadTimer *time.Timer
+	var reloadPending bool
+
+	if t.watchDebounceInterval > 0 {
+		reloadTimer = time.NewTimer(t.watchDebounceInterval)
+		if !reloadTimer.Stop() {
+			<-reloadTimer.C // Drain if already fired
+		}
+	}
+
+	// Update resetTimer function:
+	resetTimer := func(reason string) {
+		log.Printf("%s", reason)
+
+		if t.watchDebounceInterval == 0 {
+			// No debouncing - trigger immediately
+			select {
+			case signals <- syscall.SIGHUP:
+			case <-ctx.Done():
+				return
+			}
+			return
+		}
+
+		if !reloadPending {
+			reloadPending = true
+		}
+
+		// Properly drain and reset timer
+		if !reloadTimer.Stop() {
+			select {
+			case <-reloadTimer.C:
+			default:
+			}
+		}
+		reloadTimer.Reset(t.watchDebounceInterval)
+	}
+
+	for {
+		select {
+		case <-ctx.Done():
+			reloadTimer.Stop()
+			mytomb.Done()
+			return
+
+		case <-changes.Modified:
+			resetTimer(fmt.Sprintf("I! Config file/directory %q modified\n", fConfig))
+
+		case <-changes.Deleted:
+			// Use select with timeout instead of blocking wait
+			timer := time.NewTimer(time.Second)
+			select {
+			case <-timer.C:
+				// Proceed with file existence check
+			case <-ctx.Done():
+				timer.Stop()
+				return
+			}
+
+			var reason string
+			if _, err := os.Stat(fConfig); err == nil {
+				reason = fmt.Sprintf("I! Config file/directory %q overwritten\n", fConfig)
+			} else {
+				reason = fmt.Sprintf("W! Config file/directory %q deleted\n", fConfig)
+			}
+			resetTimer(reason)
+
+		case <-changes.Truncated:
+			resetTimer(fmt.Sprintf("I! Config file/directory %q truncated\n", fConfig))
+
+		case <-changes.Created:
+			resetTimer(fmt.Sprintf("I! Config directory %q has new file(s)\n", fConfig))
+
+		case <-func() <-chan time.Time {
+			if reloadTimer != nil {
+				return reloadTimer.C
+			}
+			// Return a channel that never fires when debouncing is disabled
+			return make(<-chan time.Time)
+		}():
+			if reloadPending {
+				log.Printf("I! Debounce period elapsed, triggering config reload for %q\n", fConfig)
+				select {
+				case signals <- syscall.SIGHUP:
+				case <-ctx.Done():
+					return
+				}
+				reloadPending = false
+			}
+
+		case <-mytomb.Dying():
+			reloadTimer.Stop()
+			log.Printf("I! Config watcher %q ended\n", fConfig)
+			return
 		}
-	case <-changes.Truncated:
-		log.Printf("I! Config file/directory %q truncated\n", fConfig)
-	case <-changes.Created:
-		log.Printf("I! Config directory %q has new file(s)\n", fConfig)
-	case <-mytomb.Dying():
-		log.Printf("I! Config watcher %q ended\n", fConfig)
-		return
 	}
-	mytomb.Done()
-	signals <- syscall.SIGHUP
 }
 
 func (*Telegraf) watchRemoteConfigs(ctx context.Context, signals chan os.Signal, interval time.Duration, remoteConfigs []string) {