Add a flag to make per-host metrics optional

When serving many hosts from one nginx, the metrics may become too
numerous for Prometheus.  Add a flag to disable the host label, so
that metrics are totalled across all hosts.

internal/ingress/controller/controller.go

@@ -87,7 +87,8 @@ type Configuration struct {
 
 	EnableProfiling bool
 
-	EnableMetrics bool
+	EnableMetrics  bool
+	MetricsPerHost bool
 
 	EnableSSLChainCompletion bool
 

internal/ingress/metric/collectors/socket.go

@@ -76,12 +76,12 @@ type SocketCollector struct {
 	metricMapping map[string]interface{}
 
 	hosts sets.String
+
+	metricsPerHost bool
 }
 
 var (
 	requestTags = []string{
-		"host",
-
 		"status",
 
 		"method",
@@ -95,7 +95,7 @@ var (
 
 // NewSocketCollector creates a new SocketCollector instance using
 // the ingress watch namespace and class used by the controller
-func NewSocketCollector(pod, namespace, class string) (*SocketCollector, error) {
+func NewSocketCollector(pod, namespace, class string, metricsPerHost bool) (*SocketCollector, error) {
 	socket := "/tmp/prometheus-nginx.socket"
 	listener, err := net.Listen("unix", socket)
 	if err != nil {
@@ -113,9 +113,16 @@ func NewSocketCollector(pod, namespace, class string) (*SocketCollector, error)
 		"controller_pod":       pod,
 	}
 
+	requestTags := requestTags
+	if metricsPerHost {
+		requestTags = append(requestTags, "host")
+	}
+
 	sc := &SocketCollector{
 		listener: listener,
 
+		metricsPerHost: metricsPerHost,
+
 		responseTime: prometheus.NewHistogramVec(
 			prometheus.HistogramOpts{
 				Name:        "response_duration_seconds",
@@ -219,8 +226,8 @@ func (sc *SocketCollector) handleMessage(msg []byte) {
 			continue
 		}
 
+		// Note these must match the order in requestTags at the top
 		requestLabels := prometheus.Labels{
-			"host":      stats.Host,
 			"status":    stats.Status,
 			"method":    stats.Method,
 			"path":      stats.Path,
@@ -228,6 +235,9 @@ func (sc *SocketCollector) handleMessage(msg []byte) {
 			"ingress":   stats.Ingress,
 			"service":   stats.Service,
 		}
+		if sc.metricsPerHost {
+			requestLabels["host"] = stats.Host
+		}
 
 		collectorLabels := prometheus.Labels{
 			"namespace": stats.Namespace,

internal/ingress/metric/collectors/socket_test.go

@@ -288,7 +288,7 @@ func TestCollector(t *testing.T) {
 		t.Run(c.name, func(t *testing.T) {
 			registry := prometheus.NewPedanticRegistry()
 
-			sc, err := NewSocketCollector("pod", "default", "ingress")
+			sc, err := NewSocketCollector("pod", "default", "ingress", true)
 			if err != nil {
 				t.Errorf("%v: unexpected error creating new SocketCollector: %v", c.name, err)
 			}

internal/ingress/metric/main.go

@@ -59,7 +59,7 @@ type collector struct {
 }
 
 // NewCollector creates a new metric collector the for ingress controller
-func NewCollector(statusPort int, registry *prometheus.Registry) (Collector, error) {
+func NewCollector(statusPort int, metricsPerHost bool, registry *prometheus.Registry) (Collector, error) {
 	podNamespace := os.Getenv("POD_NAMESPACE")
 	if podNamespace == "" {
 		podNamespace = "default"
@@ -77,7 +77,7 @@ func NewCollector(statusPort int, registry *prometheus.Registry) (Collector, err
 		return nil, err
 	}
 
-	s, err := collectors.NewSocketCollector(podName, podNamespace, class.IngressClass)
+	s, err := collectors.NewSocketCollector(podName, podNamespace, class.IngressClass, metricsPerHost)
 	if err != nil {
 		return nil, err
 	}