DataDog and StatsD Metrics Support

* Added support for DataDog and StatsD monitoring
* Added documentation

middlewares/statsd.go

@@ -0,0 +1,85 @@
+package middlewares
+
+import (
+	"time"
+
+	"github.com/containous/traefik/log"
+	"github.com/containous/traefik/safe"
+	"github.com/containous/traefik/types"
+	kitlog "github.com/go-kit/kit/log"
+	"github.com/go-kit/kit/metrics"
+	"github.com/go-kit/kit/metrics/statsd"
+)
+
+var _ Metrics = (Metrics)(nil)
+
+var statsdClient = statsd.New("traefik.", kitlog.LoggerFunc(func(keyvals ...interface{}) error {
+	log.Info(keyvals)
+	return nil
+}))
+var statsdTicker *time.Ticker
+
+// Statsd is an Implementation for Metrics that exposes statsd metrics for the latency
+// and the number of requests partitioned by status code and method.
+// - number of requests partitioned by status code and method
+// - request durations
+// - amount of retries happened
+type Statsd struct {
+	reqsCounter          metrics.Counter
+	reqDurationHistogram metrics.Histogram
+	retryCounter         metrics.Counter
+}
+
+func (s *Statsd) getReqsCounter() metrics.Counter {
+	return s.reqsCounter
+}
+
+func (s *Statsd) getReqDurationHistogram() metrics.Histogram {
+	return s.reqDurationHistogram
+}
+
+func (s *Statsd) getRetryCounter() metrics.Counter {
+	return s.retryCounter
+}
+
+// NewStatsD creates new instance of StatsD
+func NewStatsD(name string) *Statsd {
+	var m Statsd
+
+	m.reqsCounter = statsdClient.NewCounter(ddMetricsReqsName, 1.0).With("service", name)
+	m.reqDurationHistogram = statsdClient.NewTiming(ddMetricsLatencyName, 1.0).With("service", name)
+
+	return &m
+}
+
+// InitStatsdClient initializes metrics pusher and creates a statsdClient if not created already
+func InitStatsdClient(config *types.Statsd) *time.Ticker {
+	if statsdTicker == nil {
+		address := config.Address
+		if len(address) == 0 {
+			address = "localhost:8125"
+		}
+		pushInterval, err := time.ParseDuration(config.PushInterval)
+		if err != nil {
+			log.Warnf("Unable to parse %s into pushInterval, using 10s as default value", config.PushInterval)
+			pushInterval = 10 * time.Second
+		}
+
+		report := time.NewTicker(pushInterval)
+
+		safe.Go(func() {
+			statsdClient.SendLoop(report.C, "udp", address)
+		})
+
+		statsdTicker = report
+	}
+	return statsdTicker
+}
+
+// StopStatsdClient stops internal statsdTicker which controls the pushing of metrics to StatsD Agent and resets it to `nil`
+func StopStatsdClient() {
+	if statsdTicker != nil {
+		statsdTicker.Stop()
+	}
+	statsdTicker = nil
+}