added metrics

Change-Id: I7727bd43911339f48e2d096f8bb43729eb65b3ad

metrics/metrics.go

@@ -0,0 +1,66 @@
+package metrics
+
+import (
+	"runtime"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	// Errors tracks http status codes for problematic requests.
+	Errors = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "errors_total",
+			Help: "Number of upstream errors",
+		},
+		[]string{"status"},
+	)
+
+	// Func tracks time spent in a function.
+	Func = prometheus.NewSummaryVec(
+		prometheus.SummaryOpts{
+			Name: "function_microseconds",
+			Help: "function timing.",
+		},
+		[]string{"route"},
+	)
+
+	// DB tracks timing of interactions with the file system.
+	DB = prometheus.NewSummaryVec(
+		prometheus.SummaryOpts{
+			Name: "db_microseconds",
+			Help: "db timing.",
+		},
+		[]string{"what"},
+	)
+)
+
+func init() {
+	prometheus.MustRegister(Errors)
+	prometheus.MustRegister(Func)
+	prometheus.MustRegister(DB)
+}
+
+// Time is a function that makes it simple to add one-line timings to function
+// calls.
+func Time() func() {
+	start := time.Now()
+	return func() {
+		elapsed := time.Since(start)
+		pc := make([]uintptr, 10)
+		runtime.Callers(2, pc)
+		f := runtime.FuncForPC(pc[0])
+
+		Func.WithLabelValues(f.Name()).Observe(float64(elapsed / time.Microsecond))
+	}
+}
+
+// DBTime makes it simple to add one-line timings to db interactions.
+func DBTime(name string) func() {
+	start := time.Now()
+	return func() {
+		elapsed := time.Since(start)
+		DB.WithLabelValues(name).Observe(float64(elapsed / time.Microsecond))
+	}
+}