JSC-62132: Add support to configure extra labels

README.md

@@ -22,3 +22,17 @@ saramaprom.ExportMetrics(metricRegistry, saramaprom.Options{})
 ```
 
 `saramaprom.Options` enables you to for example configure how often the metrics are refreshed, namespace of the metrics, etc.
+
+Multiple metric registries can be defined to not mix values of several Kafka cluster.
+But in that case the prometheus metrics have to be distinguished by labels. Use `ExtraLabels` option for that:
+```
+// create new registry and export metrics for cluster Foo 
+configFoo := sarama.NewConfig()
+configFoo.MetricRegistry = metrics.NewRegistry()
+saramaprom.ExportMetrics(configFoo.MetricRegistry, saramaprom.Options{ExtraLabels: map[string]string{"cluster": "foo"}})
+
+// create new registry and export metrics for cluster Bar 
+configBar := sarama.NewConfig()
+configBar.MetricRegistry = metrics.NewRegistry()
+saramaprom.ExportMetrics(configBar.MetricRegistry, saramaprom.Options{ExtraLabels: map[string]string{"cluster": "bar"}})
+```

exporter.go

@@ -43,6 +43,9 @@ func (c *exporter) gaugeFromNameAndValue(name string, val float64) error {
 	if skip {
 		return nil
 	}
+	for n, v := range c.opt.ExtraLabels {
+		labels[n] = v
+	}
 
 	if _, exists := c.gauges[name]; !exists {
 		labelNames := make([]string, 0, len(labels))
@@ -151,6 +154,9 @@ func (c *exporter) summaryFromNameAndMetric(name string, goMetric interface{}, q
 	if skip {
 		return nil
 	}
+	for n, v := range c.opt.ExtraLabels {
+		labels[n] = v
+	}
 
 	desc := prometheus.NewDesc(
 		prometheus.BuildFQName(

saramaprom.go

@@ -20,6 +20,9 @@ type Options struct {
 	Namespace string
 	Subsystem string
 
+	// Extra labels to be added to all metrics. Beware, this will override the default label value if configured with same name.
+	ExtraLabels prometheus.Labels
+
 	// RefreshInterval specifies interval between updating metrics. Default 1s.
 	RefreshInterval time.Duration
 }

saramaprom_test.go

@@ -54,12 +54,13 @@ func TestLabels(t *testing.T) {
 		Namespace:          "test",
 		Subsystem:          "subsys",
 		PrometheusRegistry: promRegistry,
+		ExtraLabels:        map[string]string{"extra": "foo"},
 	})
 
 	t.Run("counter1-for-broker-123", func(t *testing.T) {
 		want := []gaugeDetails{{
 			name:        "test_subsys_counter1",
-			labels:      map[string]string{"broker": "123", "topic": ""},
+			labels:      map[string]string{"broker": "123", "topic": "", "extra": "foo"},
 			gaugeValues: []float64{0},
 		}}
 		got := getMetricDetails(promRegistry, "test_subsys_counter1")
@@ -68,7 +69,7 @@ func TestLabels(t *testing.T) {
 	t.Run("counter2-for-topic-abc", func(t *testing.T) {
 		want := []gaugeDetails{{
 			name:        "test_subsys_counter2",
-			labels:      map[string]string{"broker": "", "topic": "abc"},
+			labels:      map[string]string{"broker": "", "topic": "abc", "extra": "foo"},
 			gaugeValues: []float64{0},
 		}}
 		got := getMetricDetails(promRegistry, "test_subsys_counter2")