using promauto package to ensure all created metrics are properly registered (#4025)

Signed-off-by: zounengren <zounengren@cmss.chinamobile.com>

plugin/health/overloaded.go

@@ -7,6 +7,7 @@ import (
 	"github.com/coredns/coredns/plugin"
 
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
 )
 
 // overloaded queries the health end point and updates a metrics showing how long it took.
@@ -39,7 +40,7 @@ func (h *health) overloaded() {
 
 var (
 	// HealthDuration is the metric used for exporting how fast we can retrieve the /health endpoint.
-	HealthDuration = prometheus.NewHistogram(prometheus.HistogramOpts{
+	HealthDuration = promauto.NewHistogram(prometheus.HistogramOpts{
 		Namespace: plugin.Namespace,
 		Subsystem: "health",
 		Name:      "request_duration_seconds",

plugin/health/setup.go

@@ -6,7 +6,6 @@ import (
 	"time"
 
 	"github.com/coredns/coredns/plugin"
-	"github.com/coredns/coredns/plugin/metrics"
 
 	"github.com/caddyserver/caddy"
 )
@@ -21,11 +20,6 @@ func setup(c *caddy.Controller) error {
 
 	h := &health{Addr: addr, stop: make(chan bool), lameduck: lame}
 
-	c.OnStartup(func() error {
-		metrics.MustRegister(c, HealthDuration)
-		return nil
-	})
-
 	c.OnStartup(h.OnStartup)
 	c.OnRestart(h.OnFinalShutdown)
 	c.OnFinalShutdown(h.OnFinalShutdown)