set cache size as gauge instead of counter

Author: davidnewhall

docs/api_docs.go

@@ -162,6 +162,26 @@ const docTemplateapi = `{
                 }
             }
         },
+        "/metrics": {
+            "get": {
+                "description": "Retreive internal application metrics.",
+                "produces": [
+                    "application/json"
+                ],
+                "tags": [
+                    "stats"
+                ],
+                "summary": "Return auth proxy metrics in open metrics format",
+                "responses": {
+                    "200": {
+                        "description": "Auth Proxy Prometheus metrics",
+                        "schema": {
+                            "type": "object"
+                        }
+                    }
+                }
+            }
+        },
         "/reload": {
             "get": {
                 "description": "Re-reads the config file and updates the no-auth/no-api-key-required paths.",

pkg/exp/metrics.go

@@ -8,21 +8,25 @@ import (
 	"golift.io/cache"
 )
 
+// CacheList is a map of label to stats functions for each cache.
 type CacheList map[string]func() *cache.Stats
 
+// CacheCollector is our input for creating metrics for our cache data.
 type CacheCollector struct {
 	Stats   CacheList
 	counter *prometheus.Desc
 }
 
+// Describe satisfies the Collector interface for prometheus.
 func (c *CacheCollector) Describe(ch chan<- *prometheus.Desc) {
 	ch <- c.counter
 }
 
+// Collect satisfies the Collector interface for prometheus.
 func (c *CacheCollector) Collect(ch chan<- prometheus.Metric) {
 	for label, stats := range c.Stats {
 		cache := stats()
-		ch <- prometheus.MustNewConstMetric(c.counter, prometheus.CounterValue, float64(cache.Size), label, "size")
+		ch <- prometheus.MustNewConstMetric(c.counter, prometheus.GaugeValue, float64(cache.Size), label, "size")
 		ch <- prometheus.MustNewConstMetric(c.counter, prometheus.CounterValue, float64(cache.Gets), label, "gets")
 		ch <- prometheus.MustNewConstMetric(c.counter, prometheus.CounterValue, float64(cache.Hits), label, "hits")
 		ch <- prometheus.MustNewConstMetric(c.counter, prometheus.CounterValue, float64(cache.Misses), label, "misses")
@@ -36,15 +40,22 @@ func (c *CacheCollector) Collect(ch chan<- prometheus.Metric) {
 	}
 }
 
+// Metrics contains the exported prometheus metrics used by the application.
 type Metrics struct {
 	QueryErrors  *prometheus.CounterVec
 	QueryMissing *prometheus.CounterVec
 	QueryTime    *prometheus.HistogramVec
 	ReqTime      *prometheus.HistogramVec
-	Cache        *prometheus.CounterVec
 	Uptime       prometheus.CounterFunc
 }
 
+// GetMetrics sets up metrics on startup.
+// @Description  Retreive internal application metrics.
+// @Summary      Return auth proxy metrics in open metrics format
+// @Tags         stats
+// @Produce      json
+// @Success      200  {object} any "Auth Proxy Prometheus metrics"
+// @Router       /metrics [get]
 func GetMetrics(collector *CacheCollector) *Metrics {
 	start := time.Now()
 	collector.counter = prometheus.NewDesc("authproxy_cache_counters", "All cache counters", []string{"cache", "counter"}, nil)