Support for exemplars in prometheusexporter (#13127)

* Adding a feature to prometheusexporter to export exemplars along with histogram metrics. Also, this PR includes client_golang v1.13.0 that contains our fix for the panic issue.

* read me update

* issue # added to unreleased yaml

exporter/prometheusexporter/README.md

@@ -18,11 +18,11 @@ The following settings can be optionally configured:
 
 - `const_labels` (no default): key/values that are applied for every exported metric.
 - `namespace` (no default): if set, exports metrics under the provided value.
-- `send_timestamps` (default = `false`): if true, sends the timestamp of the underlying
-  metric sample in the response.
+- `send_timestamps` (default = `false`): if true, sends the timestamp of the underlying metric sample in the response.
 - `metric_expiration` (default = `5m`): defines how long metrics are exposed without updates
 - `resource_to_telemetry_conversion`
   - `enabled` (default = false): If `enabled` is `true`, all the resource attributes will be converted to metric labels by default.
+- `enable_open_metrics`: (default = `false`): If true, metrics will be exported using the OpenMetrics format. Exemplars are only exported in the OpenMetrics format.
 
 Example:
 
@@ -40,6 +40,7 @@ exporters:
       "another label": spaced value
     send_timestamps: true
     metric_expiration: 180m
+    enable_open_metrics: true
     resource_to_telemetry_conversion:
       enabled: true
 ```

exporter/prometheusexporter/collector.go

@@ -217,11 +217,36 @@ func (c *collector) convertDoubleHistogram(metric pmetric.Metric, resourceAttrs
 		points[bucket] = cumCount
 	}
 
+	arrLen := ip.Exemplars().Len()
+	exemplars := make([]prometheus.Exemplar, arrLen)
+	for i := 0; i < arrLen; i++ {
+		e := ip.Exemplars().At(i)
+
+		labels := make(prometheus.Labels, e.FilteredAttributes().Len())
+		e.FilteredAttributes().Range(func(k string, v pcommon.Value) bool {
+			labels[k] = v.AsString()
+			return true
+		})
+
+		exemplars[i] = prometheus.Exemplar{
+			Value:     e.DoubleVal(),
+			Labels:    labels,
+			Timestamp: e.Timestamp().AsTime(),
+		}
+	}
+
 	m, err := prometheus.NewConstHistogram(desc, ip.Count(), ip.Sum(), points, attributes...)
 	if err != nil {
 		return nil, err
 	}
 
+	if arrLen > 0 {
+		m, err = prometheus.NewMetricWithExemplars(m, exemplars...)
+		if err != nil {
+			return nil, err
+		}
+	}
+
 	if c.sendTimestamps {
 		return prometheus.NewMetricWithTimestamp(ip.Timestamp().AsTime(), m), nil
 	}

exporter/prometheusexporter/collector_test.go

@@ -97,6 +97,100 @@ func TestConvertInvalidMetric(t *testing.T) {
 	}
 }
 
+func TestConvertDoubleHistogramExemplar(t *testing.T) {
+	// initialize empty histogram
+	metric := pmetric.NewMetric()
+	metric.SetDataType(pmetric.MetricDataTypeHistogram)
+	metric.SetName("test_metric")
+	metric.SetDescription("this is test metric")
+	metric.SetUnit("T")
+
+	// initialize empty datapoint
+	hd := metric.Histogram().DataPoints().AppendEmpty()
+
+	bounds := pcommon.NewImmutableFloat64Slice([]float64{5, 25, 90})
+	hd.SetExplicitBounds(bounds)
+	bc := pcommon.NewImmutableUInt64Slice([]uint64{2, 35, 70})
+	hd.SetBucketCounts(bc)
+
+	exemplarTs, _ := time.Parse("unix", "Mon Jan _2 15:04:05 MST 2006")
+	exemplars := []prometheus.Exemplar{
+		{
+			Timestamp: exemplarTs,
+			Value:     3,
+			Labels:    prometheus.Labels{"test_label_0": "label_value_0"},
+		},
+		{
+			Timestamp: exemplarTs,
+			Value:     50,
+			Labels:    prometheus.Labels{"test_label_1": "label_value_1"},
+		},
+		{
+			Timestamp: exemplarTs,
+			Value:     78,
+			Labels:    prometheus.Labels{"test_label_2": "label_value_2"},
+		},
+		{
+			Timestamp: exemplarTs,
+			Value:     100,
+			Labels:    prometheus.Labels{"test_label_3": "label_value_3"},
+		},
+	}
+
+	// add each exemplar value to the metric
+	for _, e := range exemplars {
+		pde := hd.Exemplars().AppendEmpty()
+		pde.SetDoubleVal(e.Value)
+		for k, v := range e.Labels {
+			pde.FilteredAttributes().InsertString(k, v)
+		}
+		pde.SetTimestamp(pcommon.NewTimestampFromTime(e.Timestamp))
+	}
+
+	pMap := pcommon.NewMap()
+
+	c := collector{
+		accumulator: &mockAccumulator{
+			metrics:            []pmetric.Metric{metric},
+			resourceAttributes: pMap,
+		},
+		logger: zap.NewNop(),
+	}
+
+	pbMetric, _ := c.convertDoubleHistogram(metric, pMap)
+	m := io_prometheus_client.Metric{}
+	err := pbMetric.Write(&m)
+	if err != nil {
+		return
+	}
+
+	buckets := m.GetHistogram().GetBucket()
+
+	require.Equal(t, 4, len(buckets))
+
+	require.Equal(t, 3.0, buckets[0].GetExemplar().GetValue())
+	require.Equal(t, int32(128654848), buckets[0].GetExemplar().GetTimestamp().GetNanos())
+	require.Equal(t, 1, len(buckets[0].GetExemplar().GetLabel()))
+	require.Equal(t, "test_label_0", buckets[0].GetExemplar().GetLabel()[0].GetName())
+	require.Equal(t, "label_value_0", buckets[0].GetExemplar().GetLabel()[0].GetValue())
+
+	require.Equal(t, 0.0, buckets[1].GetExemplar().GetValue())
+	require.Equal(t, int32(0), buckets[1].GetExemplar().GetTimestamp().GetNanos())
+	require.Equal(t, 0, len(buckets[1].GetExemplar().GetLabel()))
+
+	require.Equal(t, 78.0, buckets[2].GetExemplar().GetValue())
+	require.Equal(t, int32(128654848), buckets[2].GetExemplar().GetTimestamp().GetNanos())
+	require.Equal(t, 1, len(buckets[2].GetExemplar().GetLabel()))
+	require.Equal(t, "test_label_2", buckets[2].GetExemplar().GetLabel()[0].GetName())
+	require.Equal(t, "label_value_2", buckets[2].GetExemplar().GetLabel()[0].GetValue())
+
+	require.Equal(t, 100.0, buckets[3].GetExemplar().GetValue())
+	require.Equal(t, int32(128654848), buckets[3].GetExemplar().GetTimestamp().GetNanos())
+	require.Equal(t, 1, len(buckets[3].GetExemplar().GetLabel()))
+	require.Equal(t, "test_label_3", buckets[3].GetExemplar().GetLabel()[0].GetName())
+	require.Equal(t, "label_value_3", buckets[3].GetExemplar().GetLabel()[0].GetValue())
+}
+
 // errorCheckCore keeps track of logged errors
 type errorCheckCore struct {
 	errorMessages []string

exporter/prometheusexporter/config.go

@@ -43,6 +43,9 @@ type Config struct {
 
 	// ResourceToTelemetrySettings defines configuration for converting resource attributes to metric labels.
 	ResourceToTelemetrySettings resourcetotelemetry.Settings `mapstructure:"resource_to_telemetry_conversion"`
+
+	// EnableOpenMetrics enables the use of the OpenMetrics encoding option for the prometheus exporter.
+	EnableOpenMetrics bool `mapstructure:"enable_open_metrics"`
 }
 
 var _ config.Exporter = (*Config)(nil)

exporter/prometheusexporter/factory.go

@@ -43,10 +43,11 @@ func NewFactory() component.ExporterFactory {
 
 func createDefaultConfig() config.Exporter {
 	return &Config{
-		ExporterSettings: config.NewExporterSettings(config.NewComponentID(typeStr)),
-		ConstLabels:      map[string]string{},
-		SendTimestamps:   false,
-		MetricExpiration: time.Minute * 5,
+		ExporterSettings:  config.NewExporterSettings(config.NewComponentID(typeStr)),
+		ConstLabels:       map[string]string{},
+		SendTimestamps:    false,
+		MetricExpiration:  time.Minute * 5,
+		EnableOpenMetrics: false,
 	}
 }
 

exporter/prometheusexporter/prometheus.go

@@ -58,8 +58,9 @@ func newPrometheusExporter(config *Config, set component.ExporterCreateSettings)
 		handler: promhttp.HandlerFor(
 			registry,
 			promhttp.HandlerOpts{
-				ErrorHandling: promhttp.ContinueOnError,
-				ErrorLog:      newPromLogger(set.Logger),
+				ErrorHandling:     promhttp.ContinueOnError,
+				ErrorLog:          newPromLogger(set.Logger),
+				EnableOpenMetrics: config.EnableOpenMetrics,
 			},
 		),
 	}, nil

unreleased/prometheusexporter-exemplars.yaml

@@ -0,0 +1,16 @@
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: prometheusexporter
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Adds a feature to prometheusexporter that enables it to export exemplars along with histogram metrics.
+
+# One or more tracking issues related to the change
+issues: [5192]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: