plugin/forward: Allow Proxy to be used outside of forward plugin. (#5951)

* plugin/forward: Move Proxy into pkg/plugin/proxy, to allow forward.Proxy to be used outside of forward plugin.

Signed-off-by: Patrick Downey <patrick.downey@dioadconsulting.com>

plugin/pkg/proxy/metrics.go

@@ -0,0 +1,49 @@
+package proxy
+
+import (
+	"github.com/coredns/coredns/plugin"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+// Variables declared for monitoring.
+var (
+	RequestCount = promauto.NewCounterVec(prometheus.CounterOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: "proxy",
+		Name:      "requests_total",
+		Help:      "Counter of requests made per upstream.",
+	}, []string{"to"})
+	RcodeCount = promauto.NewCounterVec(prometheus.CounterOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: "proxy",
+		Name:      "responses_total",
+		Help:      "Counter of responses received per upstream.",
+	}, []string{"rcode", "to"})
+	RequestDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: "proxy",
+		Name:      "request_duration_seconds",
+		Buckets:   plugin.TimeBuckets,
+		Help:      "Histogram of the time each request took.",
+	}, []string{"to", "rcode"})
+	HealthcheckFailureCount = promauto.NewCounterVec(prometheus.CounterOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: "proxy",
+		Name:      "healthcheck_failures_total",
+		Help:      "Counter of the number of failed healthchecks.",
+	}, []string{"to"})
+	ConnCacheHitsCount = promauto.NewCounterVec(prometheus.CounterOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: "proxy",
+		Name:      "conn_cache_hits_total",
+		Help:      "Counter of connection cache hits per upstream and protocol.",
+	}, []string{"to", "proto"})
+	ConnCacheMissesCount = promauto.NewCounterVec(prometheus.CounterOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: "proxy",
+		Name:      "conn_cache_misses_total",
+		Help:      "Counter of connection cache misses per upstream and protocol.",
+	}, []string{"to", "proto"})
+)