Add metrics for cache hits/misses (#375)

* Add metrics for cache hits/misses

Add counters for cache middleware hits and misses.

* Add test for cache middleware hit/miss counters.

* Fix cache hit metric incrementing.

* Add cache hit/miss metrics to dnssec middleware.

* Update README metric documentation.

1 files changed, 16 insertions, 0 deletions

diff --git a/middleware/dnssec/handler.go b/middleware/dnssec/handler.go
index 2b7730083..4c1621c8b 100644
--- a/middleware/dnssec/handler.go
+++ b/middleware/dnssec/handler.go
@@ -53,6 +53,20 @@ var (
 		Name:      "cache_capacity",
 		Help:      "The dnssec cache's capacity.",
 	}, []string{"type"})
+
+	cacheHits = prometheus.NewCounter(prometheus.CounterOpts{
+		Namespace: middleware.Namespace,
+		Subsystem: subsystem,
+		Name:      "cache_hits_total",
+		Help:      "The count of cache hits.",
+	})
+
+	cacheMisses = prometheus.NewCounter(prometheus.CounterOpts{
+		Namespace: middleware.Namespace,
+		Subsystem: subsystem,
+		Name:      "cache_misses_total",
+		Help:      "The count of cache misses.",
+	})
 )
 
 // Name implements the Handler interface.
@@ -63,4 +77,6 @@ const subsystem = "dnssec"
 func init() {
 	prometheus.MustRegister(cacheSize)
 	prometheus.MustRegister(cacheCapacity)
+	prometheus.MustRegister(cacheHits)
+	prometheus.MustRegister(cacheMisses)
 }