Record scrape health timeseries per target.

model/labelname.go

@@ -13,11 +13,16 @@
 
 package model
 
-// The label name used to indicate the metric name of a timeseries.
-const MetricNameLabel = LabelName("name")
-
-// The label name used to indicate the job from which a timeseries was scraped.
-const JobLabel = LabelName("job")
+const (
+	// The label name indicating the metric name of a timeseries.
+	MetricNameLabel = LabelName("name")
+	// The label name indicating the job from which a timeseries was scraped.
+	JobLabel = LabelName("job")
+	// The label name indicating the instance from which a timeseries was scraped.
+	InstanceLabel = LabelName("instance")
+	// The metric name for the synthetic health variable.
+	ScrapeHealthMetricName = LabelValue("up")
+)
 
 // A LabelName is a key for a LabelSet or Metric.  It has a value associated
 // therewith.

retrieval/target.go

@@ -24,10 +24,6 @@ import (
 	"time"
 )
 
-const (
-	instance = "instance"
-)
-
 var (
 	localhostRepresentations = []string{"http://127.0.0.1", "http://localhost"}
 )
@@ -140,14 +136,42 @@ func NewTarget(address string, deadline time.Duration, baseLabels model.LabelSet
 	return target
 }
 
+func (t *target) recordScrapeHealth(results chan format.Result, timestamp time.Time, healthy bool) {
+	metric := model.Metric{}
+	for label, value := range t.baseLabels {
+		metric[label] = value
+	}
+	metric[model.MetricNameLabel] = model.ScrapeHealthMetricName
+
+	healthValue := model.SampleValue(0)
+	if healthy {
+		healthValue = model.SampleValue(1)
+	}
+
+	sample := model.Sample{
+		Metric:    metric,
+		Timestamp: timestamp,
+		Value:     healthValue,
+	}
+
+	results <- format.Result{
+		Err:    nil,
+		Sample: sample,
+	}
+}
+
 func (t *target) Scrape(earliest time.Time, results chan format.Result) (err error) {
+	now := time.Now()
+
 	defer func() {
 		futureState := t.state
 
 		switch err {
 		case nil:
+			t.recordScrapeHealth(results, now, true)
 			futureState = ALIVE
 		default:
+			t.recordScrapeHealth(results, now, false)
 			futureState = UNREACHABLE
 		}
 
@@ -162,8 +186,6 @@ func (t *target) Scrape(earliest time.Time, results chan format.Result) (err err
 			done <- true
 		}()
 
-		now := time.Now()
-
 		var resp *http.Response // Don't shadow "err" from the enclosing function.
 		resp, err = http.Get(t.Address())
 		if err != nil {
@@ -179,7 +201,7 @@ func (t *target) Scrape(earliest time.Time, results chan format.Result) (err err
 
 		// XXX: This is a wart; we need to handle this more gracefully down the
 		//      road, especially once we have service discovery support.
-		baseLabels := model.LabelSet{instance: model.LabelValue(t.Address())}
+		baseLabels := model.LabelSet{model.InstanceLabel: model.LabelValue(t.Address())}
 		for baseLabel, baseValue := range t.baseLabels {
 			baseLabels[baseLabel] = baseValue
 		}

retrieval/target_test.go

@@ -25,7 +25,7 @@ func TestTargetScrapeUpdatesState(t *testing.T) {
 		state:     UNKNOWN,
 		address:   "bad schema",
 	}
-	testTarget.Scrape(time.Time{}, make(chan format.Result))
+	testTarget.Scrape(time.Time{}, make(chan format.Result, 2))
 	if testTarget.state != UNREACHABLE {
 		t.Errorf("Expected target state %v, actual: %v", UNREACHABLE, testTarget.state)
 	}