target tags can rewrite labels deined in categraf config file (#1321)

Co-authored-by: Nallenz <godloveallen@foxmail.com>

etc/server.conf

@@ -16,6 +16,9 @@ DisableUsageReport = true
 # config | database
 ReaderFrom = "config"
 
+# if true, target tags can rewrite labels defined in categraf config file
+LabelRewrite = false
+
 [Log]
 # log write dir
 Dir = "logs"

src/server/common/label_append.go

@@ -12,13 +12,17 @@ func AppendLabels(pt *prompb.TimeSeries, target *models.Target) {
 		return
 	}
 
-	labelKeys := make(map[string]struct{})
+	labelKeys := make(map[string]int)
 	for j := 0; j < len(pt.Labels); j++ {
-		labelKeys[pt.Labels[j].Name] = struct{}{}
+		labelKeys[pt.Labels[j].Name] = j
 	}
 
 	for key, value := range target.TagsMap {
-		if _, has := labelKeys[key]; has {
+		if index, has := labelKeys[key]; has {
+			// overwrite labels
+			if config.C.LabelRewrite {
+				pt.Labels[index].Value = value
+			}
 			continue
 		}
 
@@ -32,7 +36,7 @@ func AppendLabels(pt *prompb.TimeSeries, target *models.Target) {
 	if _, has := labelKeys[config.C.BusiGroupLabelKey]; has {
 		return
 	}
-
+	// 将业务组名称作为tag附加到数据上
 	if target.GroupId > 0 && len(config.C.BusiGroupLabelKey) > 0 {
 		bg := memsto.BusiGroupCache.GetByBusiGroupId(target.GroupId)
 		if bg == nil {

src/server/config/config.go

@@ -267,6 +267,7 @@ type Config struct {
 	EngineDelay        int64
 	DisableUsageReport bool
 	ReaderFrom         string
+	LabelRewrite	   bool
 	ForceUseServerTS   bool
 	Log                logx.Config
 	HTTP               httpx.Config