[cluster/vminsert]:add reload -relabelConfig on the request to /-/reload (#3923)

When I use vminsert's `relabelConfig`, I found that now there is no
reloaded api. However, `vminsert` under `VM-Single` has it. So, I hope
to add it to the `cluster/vminster`.

---------

Signed-off-by: z-anshun <1179798460@qq.com>
Co-authored-by: Nikolay <nik@victoriametrics.com>

app/vminsert/main.go

@@ -187,6 +187,8 @@ func main() {
 	netstorage.MustStop()
 	logger.Infof("successfully stopped netstorage in %.3f seconds", time.Since(startTime).Seconds())
 
+	relabel.Stop()
+
 	fs.MustStopDirRemover()
 
 	logger.Infof("the vminsert has been stopped")
@@ -384,6 +386,10 @@ func requestHandler(w http.ResponseWriter, r *http.Request) bool {
 		w.Header().Set("Content-Type", "application/json")
 		fmt.Fprintf(w, `{}`)
 		return true
+	case "/-/reload":
+		procutil.SelfSIGHUP()
+		w.WriteHeader(http.StatusNoContent)
+		return true
 	default:
 		// This is not our link
 		return false

app/vminsert/relabel/relabel.go

@@ -3,7 +3,9 @@ package relabel
 import (
 	"flag"
 	"fmt"
+	"sync"
 	"sync/atomic"
+	"time"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/fasttime"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
@@ -22,6 +24,9 @@ var (
 	usePromCompatibleNaming = flag.Bool("usePromCompatibleNaming", false, "Whether to replace characters unsupported by Prometheus with underscores "+
 		"in the ingested metric names and label names. For example, foo.bar{a.b='c'} is transformed into foo_bar{a_b='c'} during data ingestion if this flag is set. "+
 		"See https://prometheus.io/docs/concepts/data_model/#metric-names-and-labels")
+
+	relabelConfigCheckInterval = flag.Duration("relabelConfigCheckInterval", 0, "Interval for checking for changes in '-relabelConfig' file. "+
+		"By default the checking is disabled. Send SIGHUP signal in order to force config check for changes")
 )
 
 // Init must be called after flag.Parse and before using the relabel package.
@@ -42,18 +47,53 @@ func Init() {
 	if len(*relabelConfig) == 0 {
 		return
 	}
+
+	globalStopChan = make(chan struct{})
+	relabelWG.Add(1)
 	go func() {
-		for range sighupCh {
-			configReloads.Inc()
-			logger.Infof("received SIGHUP; reloading -relabelConfig=%q...", *relabelConfig)
-			pcs, err := loadRelabelConfig()
-			if err != nil {
-				configReloadErrors.Inc()
-				configSuccess.Set(0)
-				logger.Errorf("cannot load the updated relabelConfig: %s; preserving the previous config", err)
-				continue
+		defer relabelWG.Done()
+		var tickerCh <-chan time.Time
+		if *relabelConfigCheckInterval > 0 {
+			ticker := time.NewTicker(*relabelConfigCheckInterval)
+			tickerCh = ticker.C
+			defer ticker.Stop()
+		}
+		for {
+			select {
+			case <-sighupCh:
+				configReloads.Inc()
+				logger.Infof("received SIGHUP; reloading -relabelConfig=%q...", *relabelConfig)
+				pcsNew, err := loadRelabelConfig()
+				if err != nil {
+					configReloadErrors.Inc()
+					configSuccess.Set(0)
+					logger.Errorf("cannot load the updated relabelConfig: %s; preserving the previous config", err)
+					continue
+				}
+				if pcsNew.String() == pcs.String() {
+					logger.Infof("nothing changed in %q", relabelConfig)
+					continue
+				}
+				pcs = pcsNew
+				pcsGlobal.Store(pcsNew)
+			case <-tickerCh:
+				pcsNew, err := loadRelabelConfig()
+				if err != nil {
+					configReloadErrors.Inc()
+					configSuccess.Set(0)
+					logger.Errorf("cannot load the updated relabelConfig: %s; preserving the previous config", err)
+					continue
+				}
+				if pcsNew.String() == pcs.String() {
+					continue
+				}
+				pcs = pcsNew
+				pcsGlobal.Store(pcsNew)
+
+			case <-globalStopChan:
+				logger.Infof("stopping relabel")
+				return
 			}
-			pcsGlobal.Store(pcs)
 			configSuccess.Set(1)
 			configTimestamp.Set(fasttime.UnixTimestamp())
 			logger.Infof("successfully reloaded -relabelConfig=%q", *relabelConfig)
@@ -61,6 +101,20 @@ func Init() {
 	}()
 }
 
+func Stop() {
+	if len(*relabelConfig) == 0 {
+		return
+	}
+
+	close(globalStopChan)
+	relabelWG.Wait()
+}
+
+var (
+	globalStopChan chan struct{}
+	relabelWG      sync.WaitGroup
+)
+
 var (
 	configReloads      = metrics.NewCounter(`vm_relabel_config_reloads_total`)
 	configReloadErrors = metrics.NewCounter(`vm_relabel_config_reloads_errors_total`)