retrieval: avoid race conditions

retrieval/target.go

@@ -142,20 +142,17 @@ func (ts *TargetStatus) setLastError(err error) {
 type Target struct {
 	// The status object for the target. It is only set once on initialization.
 	status *TargetStatus
-	// The HTTP client used to scrape the target's endpoint.
-	httpClient *http.Client
-
 	// Closing scraperStopping signals that scraping should stop.
 	scraperStopping chan struct{}
 	// Closing scraperStopped signals that scraping has been stopped.
 	scraperStopped chan struct{}
 	// Channel to buffer ingested samples.
 	ingestedSamples chan clientmodel.Samples
-	// Metric relabel configuration.
-	metricRelabelConfigs []*config.RelabelConfig
 
 	// Mutex protects the members below.
 	sync.RWMutex
+	// The HTTP client used to scrape the target's endpoint.
+	httpClient *http.Client
 	// url is the URL to be scraped. Its host is immutable.
 	url *url.URL
 	// Labels before any processing.
@@ -169,6 +166,8 @@ type Target struct {
 	// Whether the target's labels have precedence over the base labels
 	// assigned by the scraping instance.
 	honorLabels bool
+	// Metric relabel configuration.
+	metricRelabelConfigs []*config.RelabelConfig
 }
 
 // NewTarget creates a reasonably configured target for querying.
@@ -331,6 +330,14 @@ func (t *Target) scrape(sampleAppender storage.SampleAppender) (err error) {
 	start := time.Now()
 	baseLabels := t.BaseLabels()
 
+	t.RLock()
+	var (
+		honorLabels          = t.honorLabels
+		httpClient           = t.httpClient
+		metricRelabelConfigs = t.metricRelabelConfigs
+	)
+	t.RUnlock()
+
 	defer func() {
 		t.status.setLastError(err)
 		recordScrapeHealth(sampleAppender, clientmodel.TimestampFromTime(start), baseLabels, t.status.Health(), time.Since(start))
@@ -342,7 +349,7 @@ func (t *Target) scrape(sampleAppender storage.SampleAppender) (err error) {
 	}
 	req.Header.Add("Accept", acceptHeader)
 
-	resp, err := t.httpClient.Do(req)
+	resp, err := httpClient.Do(req)
 	if err != nil {
 		return err
 	}
@@ -368,7 +375,7 @@ func (t *Target) scrape(sampleAppender storage.SampleAppender) (err error) {
 
 	for samples := range t.ingestedSamples {
 		for _, s := range samples {
-			if t.honorLabels {
+			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 {
@@ -387,10 +394,10 @@ func (t *Target) scrape(sampleAppender storage.SampleAppender) (err error) {
 				}
 			}
 			// Avoid the copy in Relabel if there are no configs.
-			if len(t.metricRelabelConfigs) > 0 {
-				labels, err := Relabel(clientmodel.LabelSet(s.Metric), t.metricRelabelConfigs...)
+			if len(metricRelabelConfigs) > 0 {
+				labels, err := Relabel(clientmodel.LabelSet(s.Metric), metricRelabelConfigs...)
 				if err != nil {
-					log.Errorf("Error while relabeling metric %s of instance %s: %s", s.Metric, t.url, err)
+					log.Errorf("Error while relabeling metric %s of instance %s: %s", s.Metric, req.URL, err)
 					continue
 				}
 				// Check if the timeseries was dropped.