Move metric modifications into SampleAppenders

retrieval/target.go

@@ -212,7 +212,9 @@ func (t *Target) Update(cfg *config.ScrapeConfig, baseLabels, metaLabels model.L
 
 	t.url.Scheme = string(baseLabels[model.SchemeLabel])
 	t.url.Path = string(baseLabels[model.MetricsPathLabel])
+
 	params := url.Values{}
+
 	for k, v := range cfg.Params {
 		params[k] = make([]string, len(v))
 		copy(params[k], v)
@@ -402,22 +404,41 @@ func (t *Target) ingest(s model.Vector) error {
 
 const acceptHeader = `application/vnd.google.protobuf;proto=io.prometheus.client.MetricFamily;encoding=delimited;q=0.7,text/plain;version=0.0.4;q=0.3,application/json;schema="prometheus/telemetry";version=0.0.2;q=0.2,*/*;q=0.1`
 
-func (t *Target) scrape(sampleAppender storage.SampleAppender) (err error) {
+func (t *Target) scrape(appender storage.SampleAppender) (err error) {
 	start := time.Now()
 	baseLabels := t.BaseLabels()
 
+	defer func(appender storage.SampleAppender) {
+		t.status.setLastError(err)
+		recordScrapeHealth(appender, start, baseLabels, t.status.Health(), time.Since(start))
+	}(appender)
+
 	t.RLock()
-	var (
-		honorLabels          = t.honorLabels
-		httpClient           = t.httpClient
-		metricRelabelConfigs = t.metricRelabelConfigs
-	)
-	t.RUnlock()
 
-	defer func() {
-		t.status.setLastError(err)
-		recordScrapeHealth(sampleAppender, start, baseLabels, t.status.Health(), time.Since(start))
-	}()
+	// The relabelAppender has to be inside the label-modifying appenders
+	// so the relabeling rules are applied to the correct label set.
+	if len(t.metricRelabelConfigs) > 0 {
+		appender = relabelAppender{
+			app:         appender,
+			relabelings: t.metricRelabelConfigs,
+		}
+	}
+
+	if t.honorLabels {
+		appender = honorLabelsAppender{
+			app:    appender,
+			labels: baseLabels,
+		}
+	} else {
+		appender = ruleLabelsAppender{
+			app:    appender,
+			labels: baseLabels,
+		}
+	}
+
+	httpClient := t.httpClient
+
+	t.RUnlock()
 
 	req, err := http.NewRequest("GET", t.URL().String(), nil)
 	if err != nil {
@@ -450,7 +471,7 @@ func (t *Target) scrape(sampleAppender storage.SampleAppender) (err error) {
 
 	go func() {
 		for {
-			// TODO(fabxc): Changex the SampleAppender interface to return an error
+			// TODO(fabxc): Change the SampleAppender interface to return an error
 			// so we can proceed based on the status and don't leak goroutines trying
 			// to append a single sample after dropping all the other ones.
 			//
@@ -468,38 +489,7 @@ func (t *Target) scrape(sampleAppender storage.SampleAppender) (err error) {
 
 	for samples := range t.ingestedSamples {
 		for _, s := range samples {
-			if honorLabels {
-				// Merge the metric with the baseLabels for labels not already set in the
-				// metric. This also considers labels explicitly set to the empty string.
-				for ln, lv := range baseLabels {
-					if _, ok := s.Metric[ln]; !ok {
-						s.Metric[ln] = lv
-					}
-				}
-			} else {
-				// Merge the ingested metric with the base label set. On a collision the
-				// value of the label is stored in a label prefixed with the exported prefix.
-				for ln, lv := range baseLabels {
-					if v, ok := s.Metric[ln]; ok && v != "" {
-						s.Metric[model.ExportedLabelPrefix+ln] = v
-					}
-					s.Metric[ln] = lv
-				}
-			}
-			// Avoid the copy in Relabel if there are no configs.
-			if len(metricRelabelConfigs) > 0 {
-				labels, err := Relabel(model.LabelSet(s.Metric), metricRelabelConfigs...)
-				if err != nil {
-					log.Errorf("Error while relabeling metric %s of instance %s: %s", s.Metric, req.URL, err)
-					continue
-				}
-				// Check if the timeseries was dropped.
-				if labels == nil {
-					continue
-				}
-				s.Metric = model.Metric(labels)
-			}
-			sampleAppender.Append(s)
+			appender.Append(s)
 		}
 	}
 
@@ -509,10 +499,69 @@ func (t *Target) scrape(sampleAppender storage.SampleAppender) (err error) {
 	return err
 }
 
+// Merges the ingested sample's metric with the label set. On a collision the
+// value of the ingested label is stored in a label prefixed with 'exported_'.
+type ruleLabelsAppender struct {
+	app    storage.SampleAppender
+	labels model.LabelSet
+}
+
+func (app ruleLabelsAppender) Append(s *model.Sample) {
+	for ln, lv := range app.labels {
+		if v, ok := s.Metric[ln]; ok && v != "" {
+			s.Metric[model.ExportedLabelPrefix+ln] = v
+		}
+		s.Metric[ln] = lv
+	}
+
+	app.app.Append(s)
+}
+
+type honorLabelsAppender struct {
+	app    storage.SampleAppender
+	labels model.LabelSet
+}
+
+// Merges the sample's metric with the given labels if the label is not
+// already present in the metric.
+// This also considers labels explicitly set to the empty string.
+func (app honorLabelsAppender) Append(s *model.Sample) {
+	for ln, lv := range app.labels {
+		if _, ok := s.Metric[ln]; !ok {
+			s.Metric[ln] = lv
+		}
+	}
+
+	app.app.Append(s)
+}
+
+// Applies a set of relabel configurations to the sample's metric
+// before actually appending it.
+type relabelAppender struct {
+	app         storage.SampleAppender
+	relabelings []*config.RelabelConfig
+}
+
+func (app relabelAppender) Append(s *model.Sample) {
+	labels, err := Relabel(model.LabelSet(s.Metric), app.relabelings...)
+	if err != nil {
+		log.Errorf("Error while relabeling metric %s: %s", s.Metric, err)
+		return
+	}
+	// Check if the timeseries was dropped.
+	if labels == nil {
+		return
+	}
+	s.Metric = model.Metric(labels)
+
+	app.app.Append(s)
+}
+
 // URL returns a copy of the target's URL.
 func (t *Target) URL() *url.URL {
 	t.RLock()
 	defer t.RUnlock()
+
 	u := &url.URL{}
 	*u = *t.url
 	return u