Add Prometheus plugin.

This allows pulling Prometheus metrics from
any client library or exporter over HTTP.

README.md

@@ -47,6 +47,7 @@ Telegraf currently has support for collecting metrics from:
 * System (memory, CPU, network, etc.)
 * Docker
 * MySQL
+* Prometheus (client libraries and exporters)
 * PostgreSQL
 * Redis
 

plugins/all/all.go

@@ -4,6 +4,7 @@ import (
 	_ "github.com/influxdb/telegraf/plugins/memcached"
 	_ "github.com/influxdb/telegraf/plugins/mysql"
 	_ "github.com/influxdb/telegraf/plugins/postgresql"
+	_ "github.com/influxdb/telegraf/plugins/prometheus"
 	_ "github.com/influxdb/telegraf/plugins/redis"
 	_ "github.com/influxdb/telegraf/plugins/system"
 )

plugins/prometheus/prometheus.go

@@ -0,0 +1,105 @@
+package prometheus
+
+import (
+	"errors"
+	"fmt"
+	"net/http"
+	"sync"
+	"time"
+
+	"github.com/influxdb/telegraf/plugins"
+	"github.com/prometheus/client_golang/extraction"
+	"github.com/prometheus/client_golang/model"
+)
+
+type Prometheus struct {
+	Urls []string
+}
+
+var sampleConfig = `
+# An array of urls to scrape metrics from.
+urls = ["http://localhost:9100/metrics"]`
+
+func (r *Prometheus) SampleConfig() string {
+	return sampleConfig
+}
+
+func (r *Prometheus) Description() string {
+	return "Read metrics from one or many prometheus clients"
+}
+
+var ErrProtocolError = errors.New("prometheus protocol error")
+
+// Reads stats from all configured servers accumulates stats.
+// Returns one of the errors encountered while gather stats (if any).
+func (g *Prometheus) Gather(acc plugins.Accumulator) error {
+	var wg sync.WaitGroup
+
+	var outerr error
+
+	for _, serv := range g.Urls {
+		wg.Add(1)
+		go func(serv string) {
+			defer wg.Done()
+			outerr = g.gatherURL(serv, acc)
+		}(serv)
+	}
+
+	wg.Wait()
+
+	return outerr
+}
+
+func (g *Prometheus) gatherURL(url string, acc plugins.Accumulator) error {
+	resp, err := http.Get(url)
+	if err != nil {
+		return fmt.Errorf("error making HTTP request to %s: %s", url, err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("%s returned HTTP status %s", url, resp.Status)
+	}
+	processor, err := extraction.ProcessorForRequestHeader(resp.Header)
+	if err != nil {
+		return fmt.Errorf("error getting extractor for %s: %s", url, err)
+	}
+
+	ingestor := &Ingester{
+		acc: acc,
+	}
+
+	options := &extraction.ProcessOptions{
+		Timestamp: model.TimestampFromTime(time.Now()),
+	}
+
+	err = processor.ProcessSingle(resp.Body, ingestor, options)
+	if err != nil {
+		return fmt.Errorf("error getting processing samples for %s: %s", url, err)
+	}
+	return nil
+}
+
+type Ingester struct {
+	acc plugins.Accumulator
+}
+
+// Ingest implements an extraction.Ingester.
+func (i *Ingester) Ingest(samples model.Samples) error {
+	for _, sample := range samples {
+		tags := map[string]string{}
+		for key, value := range sample.Metric {
+			if key == model.MetricNameLabel {
+				continue
+			}
+			tags[string(key)] = string(value)
+		}
+		i.acc.Add(string(sample.Metric[model.MetricNameLabel]), float64(sample.Value), tags)
+	}
+	return nil
+}
+
+func init() {
+	plugins.Add("prometheus", func() plugins.Plugin {
+		return &Prometheus{}
+	})
+}

plugins/prometheus/prometheus_test.go

@@ -0,0 +1,56 @@
+package prometheus
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/influxdb/telegraf/testutil"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+
+const sampleTextFormat = `# HELP go_gc_duration_seconds A summary of the GC invocation durations.
+# TYPE go_gc_duration_seconds summary
+go_gc_duration_seconds{quantile="0"} 0.00010425500000000001
+go_gc_duration_seconds{quantile="0.25"} 0.000139108
+go_gc_duration_seconds{quantile="0.5"} 0.00015749400000000002
+go_gc_duration_seconds{quantile="0.75"} 0.000331463
+go_gc_duration_seconds{quantile="1"} 0.000667154
+go_gc_duration_seconds_sum 0.0018183950000000002
+go_gc_duration_seconds_count 7
+# HELP go_goroutines Number of goroutines that currently exist.
+# TYPE go_goroutines gauge
+go_goroutines 15
+`
+
+func TestPrometheusGeneratesMetrics(t *testing.T) {
+        ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+            fmt.Fprintln(w, sampleTextFormat)
+          }))
+	defer ts.Close()
+
+	p := &Prometheus{
+		Urls: []string{ts.URL},
+	}
+
+	var acc testutil.Accumulator
+
+	err := p.Gather(&acc)
+	require.NoError(t, err)
+
+	expected := []struct {
+		name  string
+		value float64
+		tags map[string]string
+	}{
+		{"go_gc_duration_seconds_count", 7, map[string]string{}},
+		{"go_goroutines", 15, map[string]string{}},
+	}
+
+	for _, e := range expected {
+		assert.NoError(t, acc.ValidateValue(e.name, e.value))
+	}
+}