Make TargetLabel in RelabelConfig a string

config/config.go

@@ -31,6 +31,7 @@ var (
 	patFileSDName = regexp.MustCompile(`^[^*]*(\*[^/]*)?\.(json|yml|yaml|JSON|YML|YAML)$`)
 	patRulePath   = regexp.MustCompile(`^[^*]*(\*[^/]*)?$`)
 	patAuthLine   = regexp.MustCompile(`((?:password|bearer_token|secret_key|client_secret):\s+)(".+"|'.+'|[^\s]+)`)
+	relabelTarget = regexp.MustCompile(`^(?:(?:[a-zA-Z_]|\$\{?[\w]+}?)+\w*)+$`)
 )
 
 // Load parses the YAML input s into a Config.
@@ -355,7 +356,6 @@ func (c *GlobalConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		gc.EvaluationInterval = DefaultGlobalConfig.EvaluationInterval
 	}
 	*c = *gc
-
 	return nil
 }
 
@@ -986,7 +986,7 @@ type RelabelConfig struct {
 	// Modulus to take of the hash of concatenated values from the source labels.
 	Modulus uint64 `yaml:"modulus,omitempty"`
 	// The label to which the resulting string is written in a replacement.
-	TargetLabel model.LabelName `yaml:"target_label,omitempty"`
+	TargetLabel string `yaml:"target_label,omitempty"`
 	// Replacement is the regex replacement pattern to be used.
 	Replacement string `yaml:"replacement,omitempty"`
 	// Action is the action to be performed for the relabeling.
@@ -1012,6 +1012,12 @@ func (c *RelabelConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if (c.Action == RelabelReplace || c.Action == RelabelHashMod) && c.TargetLabel == "" {
 		return fmt.Errorf("relabel configuration for %s action requires 'target_label' value", c.Action)
 	}
+	if c.Action == RelabelReplace && !relabelTarget.Match([]byte(c.TargetLabel)) {
+		return fmt.Errorf("%q is invalid 'target_label' for %s action", c.TargetLabel, c.Action)
+	}
+	if c.Action == RelabelHashMod && !model.LabelNameRE.Match([]byte(c.TargetLabel)) {
+		return fmt.Errorf("%q is invalid 'target_label' for %s action", c.TargetLabel, c.Action)
+	}
 	return nil
 }
 

relabel/relabel.go

@@ -61,20 +61,20 @@ func relabel(labels model.LabelSet, cfg *config.RelabelConfig) model.LabelSet {
 		if indexes == nil {
 			break
 		}
-		target := model.LabelName(cfg.Regex.ExpandString([]byte{}, string(cfg.TargetLabel), val, indexes))
+		target := model.LabelName(cfg.Regex.ExpandString([]byte{}, cfg.TargetLabel, val, indexes))
 		if !target.IsValid() {
-			delete(labels, cfg.TargetLabel)
+			delete(labels, model.LabelName(cfg.TargetLabel))
 			break
 		}
 		res := cfg.Regex.ExpandString([]byte{}, cfg.Replacement, val, indexes)
 		if len(res) == 0 {
-			delete(labels, cfg.TargetLabel)
+			delete(labels, model.LabelName(cfg.TargetLabel))
 			break
 		}
 		labels[target] = model.LabelValue(res)
 	case config.RelabelHashMod:
 		mod := sum64(md5.Sum([]byte(val))) % cfg.Modulus
-		labels[cfg.TargetLabel] = model.LabelValue(fmt.Sprintf("%d", mod))
+		labels[model.LabelName(cfg.TargetLabel)] = model.LabelValue(fmt.Sprintf("%d", mod))
 	case config.RelabelLabelMap:
 		out := make(model.LabelSet, len(labels))
 		// Take a copy to avoid infinite loops.

relabel/relabel_test.go

@@ -38,7 +38,7 @@ func TestRelabel(t *testing.T) {
 				{
 					SourceLabels: model.LabelNames{"a"},
 					Regex:        config.MustNewRegexp("f(.*)"),
-					TargetLabel:  model.LabelName("d"),
+					TargetLabel:  "d",
 					Separator:    ";",
 					Replacement:  "ch${1}-ch${1}",
 					Action:       config.RelabelReplace,
@@ -61,7 +61,7 @@ func TestRelabel(t *testing.T) {
 				{
 					SourceLabels: model.LabelNames{"a", "b"},
 					Regex:        config.MustNewRegexp("f(.*);(.*)r"),
-					TargetLabel:  model.LabelName("a"),
+					TargetLabel:  "a",
 					Separator:    ";",
 					Replacement:  "b${1}${2}m", // boobam
 					Action:       config.RelabelReplace,
@@ -69,7 +69,7 @@ func TestRelabel(t *testing.T) {
 				{
 					SourceLabels: model.LabelNames{"c", "a"},
 					Regex:        config.MustNewRegexp("(b).*b(.*)ba(.*)"),
-					TargetLabel:  model.LabelName("d"),
+					TargetLabel:  "d",
 					Separator:    ";",
 					Replacement:  "$1$2$2$3",
 					Action:       config.RelabelReplace,
@@ -94,7 +94,7 @@ func TestRelabel(t *testing.T) {
 				}, {
 					SourceLabels: model.LabelNames{"a"},
 					Regex:        config.MustNewRegexp("f(.*)"),
-					TargetLabel:  model.LabelName("d"),
+					TargetLabel:  "d",
 					Separator:    ";",
 					Replacement:  "ch$1-ch$1",
 					Action:       config.RelabelReplace,
@@ -124,7 +124,7 @@ func TestRelabel(t *testing.T) {
 				{
 					SourceLabels: model.LabelNames{"a"},
 					Regex:        config.MustNewRegexp(".*(b).*"),
-					TargetLabel:  model.LabelName("d"),
+					TargetLabel:  "d",
 					Separator:    ";",
 					Replacement:  "$1",
 					Action:       config.RelabelReplace,
@@ -202,7 +202,7 @@ func TestRelabel(t *testing.T) {
 				{
 					SourceLabels: model.LabelNames{"a"},
 					Regex:        config.MustNewRegexp("f"),
-					TargetLabel:  model.LabelName("b"),
+					TargetLabel:  "b",
 					Replacement:  "bar",
 					Action:       config.RelabelReplace,
 				},
@@ -220,7 +220,7 @@ func TestRelabel(t *testing.T) {
 			relabel: []*config.RelabelConfig{
 				{
 					SourceLabels: model.LabelNames{"c"},
-					TargetLabel:  model.LabelName("d"),
+					TargetLabel:  "d",
 					Separator:    ";",
 					Action:       config.RelabelHashMod,
 					Modulus:      1000,
@@ -287,7 +287,7 @@ func TestRelabel(t *testing.T) {
 					Regex:        config.MustNewRegexp("some-([^-]+)-([^,]+)"),
 					Action:       config.RelabelReplace,
 					Replacement:  "${2}",
-					TargetLabel:  model.LabelName("${1}"),
+					TargetLabel:  "${1}",
 				},
 			},
 			output: model.LabelSet{
@@ -305,7 +305,7 @@ func TestRelabel(t *testing.T) {
 					Regex:        config.MustNewRegexp("some-([^-]+)-([^,]+)"),
 					Action:       config.RelabelReplace,
 					Replacement:  "${3}",
-					TargetLabel:  model.LabelName("${1}"),
+					TargetLabel:  "${1}",
 				},
 			},
 			output: model.LabelSet{
@@ -322,21 +322,21 @@ func TestRelabel(t *testing.T) {
 					Regex:        config.MustNewRegexp("some-([^-]+)-([^,]+)"),
 					Action:       config.RelabelReplace,
 					Replacement:  "${1}",
-					TargetLabel:  model.LabelName("${3}"),
+					TargetLabel:  "${3}",
 				},
 				{
 					SourceLabels: model.LabelNames{"a"},
 					Regex:        config.MustNewRegexp("some-([^-]+)-([^,]+)"),
 					Action:       config.RelabelReplace,
 					Replacement:  "${1}",
-					TargetLabel:  model.LabelName("0${3}"),
+					TargetLabel:  "0${3}",
 				},
 				{
 					SourceLabels: model.LabelNames{"a"},
 					Regex:        config.MustNewRegexp("some-([^-]+)-([^,]+)"),
 					Action:       config.RelabelReplace,
 					Replacement:  "${1}",
-					TargetLabel:  model.LabelName("-${3}"),
+					TargetLabel:  "-${3}",
 				},
 			},
 			output: model.LabelSet{
@@ -353,21 +353,21 @@ func TestRelabel(t *testing.T) {
 					Regex:        config.MustNewRegexp("(?:.+,|^)path:(/[^,]+).*"),
 					Action:       config.RelabelReplace,
 					Replacement:  "${1}",
-					TargetLabel:  model.LabelName("__metrics_path__"),
+					TargetLabel:  "__metrics_path__",
 				},
 				{
 					SourceLabels: model.LabelNames{"__meta_sd_tags"},
 					Regex:        config.MustNewRegexp("(?:.+,|^)job:([^,]+).*"),
 					Action:       config.RelabelReplace,
 					Replacement:  "${1}",
-					TargetLabel:  model.LabelName("job"),
+					TargetLabel:  "job",
 				},
 				{
 					SourceLabels: model.LabelNames{"__meta_sd_tags"},
 					Regex:        config.MustNewRegexp("(?:.+,|^)label:([^=]+)=([^,]+).*"),
 					Action:       config.RelabelReplace,
 					Replacement:  "${2}",
-					TargetLabel:  model.LabelName("${1}"),
+					TargetLabel:  "${1}",
 				},
 			},
 			output: model.LabelSet{