DataDog and StatsD Metrics Support

* Added support for DataDog and StatsD monitoring
* Added documentation

vendor/github.com/go-kit/kit/metrics/multi/multi.go

@@ -0,0 +1,79 @@
+// Package multi provides adapters that send observations to multiple metrics
+// simultaneously. This is useful if your service needs to emit to multiple
+// instrumentation systems at the same time, for example if your organization is
+// transitioning from one system to another.
+package multi
+
+import "github.com/go-kit/kit/metrics"
+
+// Counter collects multiple individual counters and treats them as a unit.
+type Counter []metrics.Counter
+
+// NewCounter returns a multi-counter, wrapping the passed counters.
+func NewCounter(c ...metrics.Counter) Counter {
+	return Counter(c)
+}
+
+// Add implements counter.
+func (c Counter) Add(delta float64) {
+	for _, counter := range c {
+		counter.Add(delta)
+	}
+}
+
+// With implements counter.
+func (c Counter) With(labelValues ...string) metrics.Counter {
+	next := make(Counter, len(c))
+	for i := range c {
+		next[i] = c[i].With(labelValues...)
+	}
+	return next
+}
+
+// Gauge collects multiple individual gauges and treats them as a unit.
+type Gauge []metrics.Gauge
+
+// NewGauge returns a multi-gauge, wrapping the passed gauges.
+func NewGauge(g ...metrics.Gauge) Gauge {
+	return Gauge(g)
+}
+
+// Set implements Gauge.
+func (g Gauge) Set(value float64) {
+	for _, gauge := range g {
+		gauge.Set(value)
+	}
+}
+
+// With implements gauge.
+func (g Gauge) With(labelValues ...string) metrics.Gauge {
+	next := make(Gauge, len(g))
+	for i := range g {
+		next[i] = g[i].With(labelValues...)
+	}
+	return next
+}
+
+// Histogram collects multiple individual histograms and treats them as a unit.
+type Histogram []metrics.Histogram
+
+// NewHistogram returns a multi-histogram, wrapping the passed histograms.
+func NewHistogram(h ...metrics.Histogram) Histogram {
+	return Histogram(h)
+}
+
+// Observe implements Histogram.
+func (h Histogram) Observe(value float64) {
+	for _, histogram := range h {
+		histogram.Observe(value)
+	}
+}
+
+// With implements histogram.
+func (h Histogram) With(labelValues ...string) metrics.Histogram {
+	next := make(Histogram, len(h))
+	for i := range h {
+		next[i] = h[i].With(labelValues...)
+	}
+	return next
+}