Add global_labels option to defaults

global_labels provides a way to add labels that will be added to
all published metrics from the exporter. If a label defined in
global_labels is also defined in a mapping, it will be overridden.

Signed-off-by: Edmund Rhudy <erhudy@users.noreply.github.com>

README.md

@@ -471,8 +471,8 @@ mappings:
 
 ### Global defaults
 
-One may also set defaults for the observer type, histogram options, summary options, and match type.
-These will be used by all mappings that do not define them.
+One may also set defaults for the observer type, histogram options, summary options, match type, and global labels.
+These will be used by all mappings that do not define them. Global labels will be overridden by labels derived from mappings.
 
 An option that can only be configured in `defaults` is `glob_disable_ordering`, which is `false` if omitted.
 By setting this to `true`, `glob` match type will not honor the occurance of rules in the mapping rules file and always treat `*` as lower priority than a concrete string.
@@ -504,6 +504,9 @@ defaults:
   match_type: glob
   glob_disable_ordering: false
   ttl: 0 # metrics do not expire
+  global_labels:
+    example1: value1
+    example2: value2
 mappings:
 # This will be a histogram using the buckets set in `defaults`.
 - match: "test.timing.*.*.*"

pkg/exporter/exporter.go

@@ -96,7 +96,17 @@ func (b *Exporter) handleEvent(thisEvent event.Event) {
 		help = mapping.HelpText
 	}
 
-	prometheusLabels := thisEvent.Labels()
+	// labels on the event will override the global labels
+	var prometheusLabels prometheus.Labels
+	if b.Mapper.Defaults.GlobalLabels != nil {
+		prometheusLabels = b.Mapper.Defaults.GlobalLabels
+		for k, v := range thisEvent.Labels() {
+			prometheusLabels[k] = v
+		}
+	} else {
+		prometheusLabels = thisEvent.Labels()
+	}
+
 	if present {
 		if mapping.Name == "" {
 			level.Debug(b.Logger).Log("msg", "The mapping generates an empty metric name", "metric_name", thisEvent.MetricName(), "match", mapping.Match)

pkg/exporter/exporter_test.go

@@ -334,6 +334,72 @@ mappings:
 	}
 }
 
+// TestGlobalLabels verifies that labels specified in defaults.global_labels
+// are merged into the labels of the event and are overridden by event labels
+func TestGlobalLabels(t *testing.T) {
+	codes := [3]string{"200", "300", "400"}
+
+	events := make(chan event.Events)
+	go func() {
+		c := event.Events{
+			&event.CounterEvent{
+				CMetricName: "counter.test.200",
+				CValue:      1,
+				CLabels:     make(map[string]string),
+			},
+			&event.CounterEvent{
+				CMetricName: "counter.test.300",
+				CValue:      1,
+				CLabels:     make(map[string]string),
+			},
+			&event.CounterEvent{
+				CMetricName: "counter.test.400",
+				CValue:      1,
+				CLabels:     map[string]string{"code": "should be overwritten"},
+			},
+		}
+		events <- c
+		close(events)
+	}()
+
+	config := `
+defaults:
+  global_labels:
+    extra1: extra1_val
+    code: should_be_overwritten
+mappings:
+- match: counter.test.*
+  name: "counter_test"
+  labels:
+    code: $1
+`
+
+	testMapper := &mapper.MetricMapper{}
+	err := testMapper.InitFromYAMLString(config)
+	if err != nil {
+		t.Fatalf("Config load error: %s %s", config, err)
+	}
+
+	ex := NewExporter(prometheus.DefaultRegisterer, testMapper, log.NewNopLogger(), eventsActions, eventsUnmapped, errorEventStats, eventStats, conflictingEventStats, metricsCount)
+	ex.Listen(events)
+
+	metrics, err := prometheus.DefaultGatherer.Gather()
+	if err != nil {
+		t.Fatalf("Cannot gather from DefaultGatherer: %v", err)
+	}
+
+	labels := map[string]string{
+		"extra1": "extra1_val",
+	}
+
+	for _, code := range codes {
+		labels["code"] = code
+		if getFloat64(metrics, "counter_test", labels) == nil {
+			t.Fatalf("Could not find metrics for counter_test code %s", code)
+		}
+	}
+}
+
 func TestHonorLabels(t *testing.T) {
 	metricName := "some_counter"
 	events := make(chan event.Events)

pkg/mapper/mapper_defaults.go

@@ -13,15 +13,20 @@
 
 package mapper
 
-import "time"
+import (
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
 
 type MapperConfigDefaults struct {
-	ObserverType        ObserverType     `yaml:"observer_type"`
-	MatchType           MatchType        `yaml:"match_type"`
-	GlobDisableOrdering bool             `yaml:"glob_disable_ordering"`
-	Ttl                 time.Duration    `yaml:"ttl"`
-	SummaryOptions      SummaryOptions   `yaml:"summary_options"`
-	HistogramOptions    HistogramOptions `yaml:"histogram_options"`
+	ObserverType        ObserverType      `yaml:"observer_type"`
+	MatchType           MatchType         `yaml:"match_type"`
+	GlobDisableOrdering bool              `yaml:"glob_disable_ordering"`
+	Ttl                 time.Duration     `yaml:"ttl"`
+	SummaryOptions      SummaryOptions    `yaml:"summary_options"`
+	HistogramOptions    HistogramOptions  `yaml:"histogram_options"`
+	GlobalLabels        prometheus.Labels `yaml:"global_labels"`
 }
 
 // mapperConfigDefaultsAlias is used to unmarshal the yaml config into mapperConfigDefaults and allows deprecated fields
@@ -35,6 +40,7 @@ type mapperConfigDefaultsAlias struct {
 	Ttl                 time.Duration     `yaml:"ttl"`
 	SummaryOptions      SummaryOptions    `yaml:"summary_options"`
 	HistogramOptions    HistogramOptions  `yaml:"histogram_options"`
+	GlobalLabels        prometheus.Labels `yaml:"global_labels"`
 }
 
 // UnmarshalYAML is a custom unmarshal function to allow use of deprecated config keys
@@ -52,6 +58,7 @@ func (d *MapperConfigDefaults) UnmarshalYAML(unmarshal func(interface{}) error)
 	d.Ttl = tmp.Ttl
 	d.SummaryOptions = tmp.SummaryOptions
 	d.HistogramOptions = tmp.HistogramOptions
+	d.GlobalLabels = tmp.GlobalLabels
 
 	// Use deprecated TimerType if necessary
 	if tmp.ObserverType == "" {