metrics: correctly register all metrics (#1335)

After initial startup, see if prometheus is loaded and if so, register
our metrics with it.
Stop doing the init() func and just use the sync.Once so we don't double
registrer our metrics.

1 files changed, 7 insertions, 12 deletions

diff --git a/plugin/dnssec/handler.go b/plugin/dnssec/handler.go
index 6fa2dd042..0fde35dd7 100644
--- a/plugin/dnssec/handler.go
+++ b/plugin/dnssec/handler.go
@@ -1,6 +1,8 @@
 package dnssec
 
 import (
+	"sync"
+
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/request"
 
@@ -42,28 +44,28 @@ func (d Dnssec) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
 var (
 	cacheSize = prometheus.NewGaugeVec(prometheus.GaugeOpts{
 		Namespace: plugin.Namespace,
-		Subsystem: subsystem,
+		Subsystem: "dnssec",
 		Name:      "cache_size",
 		Help:      "The number of elements in the dnssec cache.",
 	}, []string{"type"})
 
 	cacheCapacity = prometheus.NewGaugeVec(prometheus.GaugeOpts{
 		Namespace: plugin.Namespace,
-		Subsystem: subsystem,
+		Subsystem: "dnssec",
 		Name:      "cache_capacity",
 		Help:      "The dnssec cache's capacity.",
 	}, []string{"type"})
 
 	cacheHits = prometheus.NewCounter(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
-		Subsystem: subsystem,
+		Subsystem: "dnssec",
 		Name:      "cache_hits_total",
 		Help:      "The count of cache hits.",
 	})
 
 	cacheMisses = prometheus.NewCounter(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
-		Subsystem: subsystem,
+		Subsystem: "dnssec",
 		Name:      "cache_misses_total",
 		Help:      "The count of cache misses.",
 	})
@@ -72,11 +74,4 @@ var (
 // Name implements the Handler interface.
 func (d Dnssec) Name() string { return "dnssec" }
 
-const subsystem = "dnssec"
-
-func init() {
-	prometheus.MustRegister(cacheSize)
-	prometheus.MustRegister(cacheCapacity)
-	prometheus.MustRegister(cacheHits)
-	prometheus.MustRegister(cacheMisses)
-}
+var once sync.Once