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

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

plugin/dnssec/metrics.go

@@ -4,25 +4,26 @@ import (
 	"github.com/coredns/coredns/plugin"
 
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
 )
 
 var (
 	// cacheSize is the number of elements in the dnssec cache.
-	cacheSize = prometheus.NewGaugeVec(prometheus.GaugeOpts{
+	cacheSize = promauto.NewGaugeVec(prometheus.GaugeOpts{
 		Namespace: plugin.Namespace,
 		Subsystem: "dnssec",
 		Name:      "cache_entries",
 		Help:      "The number of elements in the dnssec cache.",
 	}, []string{"server", "type"})
 	// cacheHits is the count of cache hits.
-	cacheHits = prometheus.NewCounterVec(prometheus.CounterOpts{
+	cacheHits = promauto.NewCounterVec(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
 		Subsystem: "dnssec",
 		Name:      "cache_hits_total",
 		Help:      "The count of cache hits.",
 	}, []string{"server"})
 	// cacheMisses is the count of cache misses.
-	cacheMisses = prometheus.NewCounterVec(prometheus.CounterOpts{
+	cacheMisses = promauto.NewCounterVec(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
 		Subsystem: "dnssec",
 		Name:      "cache_misses_total",

plugin/dnssec/setup.go

@@ -8,7 +8,6 @@ import (
 
 	"github.com/coredns/coredns/core/dnsserver"
 	"github.com/coredns/coredns/plugin"
-	"github.com/coredns/coredns/plugin/metrics"
 	"github.com/coredns/coredns/plugin/pkg/cache"
 	clog "github.com/coredns/coredns/plugin/pkg/log"
 
@@ -30,11 +29,6 @@ func setup(c *caddy.Controller) error {
 		return New(zones, keys, splitkeys, next, ca)
 	})
 
-	c.OnStartup(func() error {
-		metrics.MustRegister(c, cacheSize, cacheHits, cacheMisses)
-		return nil
-	})
-
 	return nil
 }