Add constLabels support via cli arg/env var

README.md

@@ -75,12 +75,14 @@ Usage of ./nginx-prometheus-exporter:
   -nginx.retry-interval duration
         An interval between retries to connect to the NGINX stub_status page/NGINX Plus API on start. The default value can be overwritten by NGINX_RETRY_INTERVAL environment variable. (default 5s)
   -nginx.scrape-uri string
-        A URI or unix domain socket path for scraping NGINX or NGINX Plus metrics. 
+        A URI or unix domain socket path for scraping NGINX or NGINX Plus metrics.
         For NGINX, the stub_status page must be available through the URI. For NGINX Plus -- the API. The default value can be overwritten by SCRAPE_URI environment variable. (default "http://127.0.0.1:8080/stub_status")
   -nginx.ssl-verify
         Perform SSL certificate verification. The default value can be overwritten by SSL_VERIFY environment variable. (default true)
   -nginx.timeout duration
         A timeout for scraping metrics from NGINX or NGINX Plus. The default value can be overwritten by TIMEOUT environment variable. (default 5s)
+  -prometheus.const-labels value
+        A comma separated list of constant labels that will be used in every metric. Format is label1=value1,label2=value2... The default value can be overwritten by CONST_LABELS environment variable.
   -web.listen-address string
         An address or unix domain socket path to listen on for web interface and telemetry. The default value can be overwritten by LISTEN_ADDRESS environment variable. (default ":9113")
   -web.telemetry-path string

collector/helper.go

@@ -5,8 +5,8 @@ import "github.com/prometheus/client_golang/prometheus"
 const nginxUp = 1
 const nginxDown = 0
 
-func newGlobalMetric(namespace string, metricName string, docString string) *prometheus.Desc {
-	return prometheus.NewDesc(namespace+"_"+metricName, docString, nil, nil)
+func newGlobalMetric(namespace string, metricName string, docString string, constLabels map[string]string) *prometheus.Desc {
+	return prometheus.NewDesc(namespace+"_"+metricName, docString, nil, constLabels)
 }
 
 func newUpMetric(namespace string) prometheus.Gauge {
@@ -16,3 +16,17 @@ func newUpMetric(namespace string) prometheus.Gauge {
 		Help:      "Status of the last metric scrape",
 	})
 }
+
+// MergeLabels merges two maps of labels.
+func MergeLabels(a map[string]string, b map[string]string) map[string]string {
+	c := make(map[string]string)
+
+	for k, v := range a {
+		c[k] = v
+	}
+	for k, v := range b {
+		c[k] = v
+	}
+
+	return c
+}

collector/helper_test.go

@@ -0,0 +1,39 @@
+package collector
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestMergeLabels(t *testing.T) {
+	tests := []struct {
+		name             string
+		mapA, mapB, want map[string]string
+	}{
+		{
+			name: "base case",
+			mapA: map[string]string{"a": "is here"},
+			mapB: map[string]string{"b": "is here"},
+			want: map[string]string{"a": "is here", "b": "is here"},
+		},
+		{
+			name: "overwrite key case",
+			mapA: map[string]string{"a": "is here"},
+			mapB: map[string]string{"b": "is here", "a": "is now here"},
+			want: map[string]string{"a": "is now here", "b": "is here"},
+		},
+		{
+			name: "empty maps case",
+			mapA: nil,
+			mapB: nil,
+			want: map[string]string{},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := MergeLabels(tt.mapA, tt.mapB); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("mergeLabels() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}

collector/nginx.go

@@ -17,17 +17,17 @@ type NginxCollector struct {
 }
 
 // NewNginxCollector creates an NginxCollector.
-func NewNginxCollector(nginxClient *client.NginxClient, namespace string) *NginxCollector {
+func NewNginxCollector(nginxClient *client.NginxClient, namespace string, constLabels map[string]string) *NginxCollector {
 	return &NginxCollector{
 		nginxClient: nginxClient,
 		metrics: map[string]*prometheus.Desc{
-			"connections_active":   newGlobalMetric(namespace, "connections_active", "Active client connections"),
-			"connections_accepted": newGlobalMetric(namespace, "connections_accepted", "Accepted client connections"),
-			"connections_handled":  newGlobalMetric(namespace, "connections_handled", "Handled client connections"),
-			"connections_reading":  newGlobalMetric(namespace, "connections_reading", "Connections where NGINX is reading the request header"),
-			"connections_writing":  newGlobalMetric(namespace, "connections_writing", "Connections where NGINX is writing the response back to the client"),
-			"connections_waiting":  newGlobalMetric(namespace, "connections_waiting", "Idle client connections"),
-			"http_requests_total":  newGlobalMetric(namespace, "http_requests_total", "Total http requests"),
+			"connections_active":   newGlobalMetric(namespace, "connections_active", "Active client connections", constLabels),
+			"connections_accepted": newGlobalMetric(namespace, "connections_accepted", "Accepted client connections", constLabels),
+			"connections_handled":  newGlobalMetric(namespace, "connections_handled", "Handled client connections", constLabels),
+			"connections_reading":  newGlobalMetric(namespace, "connections_reading", "Connections where NGINX is reading the request header", constLabels),
+			"connections_writing":  newGlobalMetric(namespace, "connections_writing", "Connections where NGINX is writing the response back to the client", constLabels),
+			"connections_waiting":  newGlobalMetric(namespace, "connections_waiting", "Idle client connections", constLabels),
+			"http_requests_total":  newGlobalMetric(namespace, "http_requests_total", "Total http requests", constLabels),
 		},
 		upMetric: newUpMetric(namespace),
 	}