prometheus_client, implement Collector interface

closes #1334

plugins/outputs/prometheus_client/prometheus_client.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"regexp"
 	"strings"
+	"sync"
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/plugins/outputs"
@@ -26,6 +27,10 @@ var (
 
 type PrometheusClient struct {
 	Listen string
+
+	metrics map[string]prometheus.Metric
+
+	sync.Mutex
 }
 
 var sampleConfig = `
@@ -34,6 +39,7 @@ var sampleConfig = `
 `
 
 func (p *PrometheusClient) Start() error {
+	prometheus.MustRegister(p)
 	defer func() {
 		if r := recover(); r != nil {
 			// recovering from panic here because there is no way to stop a
@@ -78,7 +84,27 @@ func (p *PrometheusClient) Description() string {
 	return "Configuration for the Prometheus client to spawn"
 }
 
+// Implements prometheus.Collector
+func (p *PrometheusClient) Describe(ch chan<- *prometheus.Desc) {
+	prometheus.NewGauge(prometheus.GaugeOpts{Name: "Dummy", Help: "Dummy"}).Describe(ch)
+}
+
+// Implements prometheus.Collector
+func (p *PrometheusClient) Collect(ch chan<- prometheus.Metric) {
+	p.Lock()
+	defer p.Unlock()
+
+	for _, m := range p.metrics {
+		ch <- m
+	}
+}
+
 func (p *PrometheusClient) Write(metrics []telegraf.Metric) error {
+	p.Lock()
+	defer p.Unlock()
+
+	p.metrics = make(map[string]prometheus.Metric)
+
 	if len(metrics) == 0 {
 		return nil
 	}
@@ -124,45 +150,23 @@ func (p *PrometheusClient) Write(metrics []telegraf.Metric) error {
 				continue
 			}
 
-			mVec := prometheus.NewUntypedVec(
-				prometheus.UntypedOpts{
-					Name: mname,
-					Help: "Telegraf collected metric",
-				},
-				labels,
-			)
-			collector, err := prometheus.RegisterOrGet(mVec)
-			if err != nil {
-				log.Printf("prometheus_client: Metric failed to register with prometheus, %s", err)
-				continue
-			}
-			mVec, ok := collector.(*prometheus.UntypedVec)
-			if !ok {
-				continue
-			}
-
+			desc := prometheus.NewDesc(mname, "Telegraf collected metric", nil, l)
+			var metric prometheus.Metric
+			var err error
 			switch val := val.(type) {
 			case int64:
-				m, err := mVec.GetMetricWith(l)
-				if err != nil {
-					log.Printf("ERROR Getting metric in Prometheus output, "+
-						"key: %s, labels: %v,\nerr: %s\n",
-						mname, l, err.Error())
-					continue
-				}
-				m.Set(float64(val))
+				metric, err = prometheus.NewConstMetric(desc, prometheus.UntypedValue, float64(val))
 			case float64:
-				m, err := mVec.GetMetricWith(l)
-				if err != nil {
-					log.Printf("ERROR Getting metric in Prometheus output, "+
-						"key: %s, labels: %v,\nerr: %s\n",
-						mname, l, err.Error())
-					continue
-				}
-				m.Set(val)
+				metric, err = prometheus.NewConstMetric(desc, prometheus.UntypedValue, val)
 			default:
 				continue
 			}
+			if err != nil {
+				log.Printf("ERROR creating prometheus metric, "+
+					"key: %s, labels: %v,\nerr: %s\n",
+					mname, l, err.Error())
+			}
+			p.metrics[desc.String()] = metric
 		}
 	}
 	return nil