Add optional Prometheus exporter to telegraf.

This will allow Telegraf plugins to be useful with Prometheus.
This is disabled by default.

agent.go

@@ -5,18 +5,21 @@ import (
 	"log"
 	"net/url"
 	"os"
+	"regexp"
 	"sort"
 	"sync"
 	"time"
 
 	"github.com/influxdb/influxdb/client"
 	"github.com/influxdb/telegraf/plugins"
+	"github.com/prometheus/client_golang/prometheus"
 )
 
 type runningPlugin struct {
 	name   string
 	plugin plugins.Plugin
 	config *ConfiguredPlugin
+	mu     sync.Mutex
 }
 
 type Agent struct {
@@ -53,6 +56,7 @@ func NewAgent(config *Config) (*Agent, error) {
 	}
 
 	config.Tags["host"] = agent.Hostname
+	prometheus.MustRegister(agent)
 
 	return agent, nil
 }
@@ -97,7 +101,7 @@ func (a *Agent) LoadPlugins() ([]string, error) {
 			return nil, err
 		}
 
-		a.plugins = append(a.plugins, &runningPlugin{name, plugin, config})
+		a.plugins = append(a.plugins, &runningPlugin{name, plugin, config, sync.Mutex{}})
 		names = append(names, name)
 	}
 
@@ -125,7 +129,9 @@ func (a *Agent) crankParallel() error {
 			acc.Prefix = plugin.name + "_"
 			acc.Config = plugin.config
 
+			plugin.mu.Lock()
 			plugin.plugin.Gather(&acc)
+			plugin.mu.Unlock()
 
 			points <- &acc
 		}(plugin)
@@ -156,7 +162,9 @@ func (a *Agent) crank() error {
 	for _, plugin := range a.plugins {
 		acc.Prefix = plugin.name + "_"
 		acc.Config = plugin.config
+		plugin.mu.Lock()
 		err := plugin.plugin.Gather(&acc)
+		plugin.mu.Unlock()
 		if err != nil {
 			return err
 		}
@@ -180,7 +188,9 @@ func (a *Agent) crankSeparate(shutdown chan struct{}, plugin *runningPlugin) err
 
 		acc.Prefix = plugin.name + "_"
 		acc.Config = plugin.config
+		plugin.mu.Lock()
 		err := plugin.plugin.Gather(&acc)
+		plugin.mu.Unlock()
 		if err != nil {
 			return err
 		}
@@ -200,6 +210,56 @@ func (a *Agent) crankSeparate(shutdown chan struct{}, plugin *runningPlugin) err
 	}
 }
 
+// Implements prometheus.Collector
+func (a *Agent) Describe(ch chan<- *prometheus.Desc) {
+	prometheus.NewGauge(prometheus.GaugeOpts{Name: "Dummy", Help: "Dummy"}).Describe(ch)
+}
+
+// Implements prometheus.Collector
+func (a *Agent) Collect(ch chan<- prometheus.Metric) {
+	var wg sync.WaitGroup
+
+	invalidNameCharRE := regexp.MustCompile(`[^a-zA-Z0-9_]`)
+
+	for _, plugin := range a.plugins {
+		wg.Add(1)
+		go func(plugin *runningPlugin) {
+			defer wg.Done()
+			var acc BatchPoints
+			acc.Prefix = plugin.name + "_"
+
+			plugin.mu.Lock()
+			err := plugin.plugin.Gather(&acc)
+			plugin.mu.Unlock()
+			if err != nil {
+				return
+			}
+
+			for _, point := range acc.Points {
+				var value float64
+				switch point.Fields["value"].(type) {
+				case float64, int64:
+					value = point.Fields["value"].(float64)
+				default:
+					continue
+				}
+				tags := map[string]string{}
+				for k, v := range point.Tags {
+					tags[invalidNameCharRE.ReplaceAllString(k, "_")] = v
+				}
+				desc := prometheus.NewDesc(invalidNameCharRE.ReplaceAllString(point.Measurement, "_"), point.Measurement, nil, tags)
+				metric, err := prometheus.NewConstMetric(desc, prometheus.UntypedValue, value)
+				if err == nil {
+					ch <- metric
+				}
+			}
+
+		}(plugin)
+	}
+
+	wg.Wait()
+}
+
 func (a *Agent) TestAllPlugins() error {
 	var names []string
 

cmd/telegraf/telegraf.go

@@ -4,12 +4,14 @@ import (
 	"flag"
 	"fmt"
 	"log"
+	"net/http"
 	"os"
 	"os/signal"
 	"strings"
 
 	"github.com/influxdb/telegraf"
 	_ "github.com/influxdb/telegraf/plugins/all"
+	"github.com/prometheus/client_golang/prometheus"
 )
 
 var fDebug = flag.Bool("debug", false, "show metrics as they're generated to stdout")
@@ -117,5 +119,21 @@ func main() {
 		f.Close()
 	}
 
+	pc := &telegraf.PrometheusCollector{ListenAddress: ""}
+	err = config.ApplyPrometheusCollector(pc)
+        if err != nil {
+                log.Fatal(err)
+        }
+	if pc.ListenAddress != "" {
+		http.Handle("/metrics", prometheus.Handler())
+                log.Printf("Listening on %s for Prometheus", pc.ListenAddress)
+                go func() {
+                    err := http.ListenAndServe(pc.ListenAddress, nil)
+                    if err != nil {
+                            log.Fatal(err)
+                    }
+                }()
+	}
+
 	ag.Run(shutdown)
 }

config.go

@@ -38,6 +38,11 @@ type Config struct {
 
 	agent               *ast.Table
 	plugins             map[string]*ast.Table
+	prometheusCollector *ast.Table
+}
+
+type PrometheusCollector struct {
+	ListenAddress string
 }
 
 func (c *Config) Plugins() map[string]*ast.Table {
@@ -85,6 +90,14 @@ func (c *Config) ApplyAgent(v interface{}) error {
 	return nil
 }
 
+func (c *Config) ApplyPrometheusCollector(v interface{}) error {
+	if c.prometheusCollector != nil {
+		return toml.UnmarshalTable(c.prometheusCollector, v)
+	}
+
+	return nil
+}
+
 func (c *Config) ApplyPlugin(name string, v interface{}) (*ConfiguredPlugin, error) {
 	cp := &ConfiguredPlugin{Name: name}
 
@@ -183,6 +196,8 @@ func LoadConfig(path string) (*Config, error) {
 			}
 		case "agent":
 			c.agent = subtbl
+		case "prometheus_collector":
+			c.prometheusCollector = subtbl
 		default:
 			c.plugins[name] = subtbl
 		}
@@ -261,6 +276,10 @@ database = "telegraf" # required.
 # debug = false
 # hostname = "prod3241"
 
+[prometheus_collector]
+# If set, expose all metrics on this address for Prometheus
+# listen_address = ":9115"
+
 # PLUGINS
 
 `