Enable Prometheus native histograms (#6524)

Add a NativeHistogramBucketFactor parameter to the use of
`NewHistogramVec` in order to enable use of Prometheus Native
Histograms.

This will store automatically computed sparse buckets in CoreDNS.
If a compatible Prometeus requests native histograms this data will
returned instead of the static buckets.

The default factor of 1.05 should provide high quality resolution data.

Signed-off-by: SuperQ <superq@gmail.com>

7 files changed, 55 insertions, 42 deletions

diff --git a/plugin/grpc/metrics.go b/plugin/grpc/metrics.go
index 2857042cd..0e8760acf 100644
--- a/plugin/grpc/metrics.go
+++ b/plugin/grpc/metrics.go
@@ -22,10 +22,11 @@ var (
 		Help:      "Counter of requests made per upstream.",
 	}, []string{"rcode", "to"})
 	RequestDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
-		Namespace: plugin.Namespace,
-		Subsystem: "grpc",
-		Name:      "request_duration_seconds",
-		Buckets:   plugin.TimeBuckets,
-		Help:      "Histogram of the time each request took.",
+		Namespace:                   plugin.Namespace,
+		Subsystem:                   "grpc",
+		Name:                        "request_duration_seconds",
+		Buckets:                     plugin.TimeBuckets,
+		NativeHistogramBucketFactor: plugin.NativeHistogramBucketFactor,
+		Help:                        "Histogram of the time each request took.",
 	}, []string{"to"})
 )
diff --git a/plugin/health/overloaded.go b/plugin/health/overloaded.go
index 160f90f02..f8b3256bf 100644
--- a/plugin/health/overloaded.go
+++ b/plugin/health/overloaded.go
@@ -67,11 +67,12 @@ func (h *health) overloaded(ctx context.Context) {
 var (
 	// HealthDuration is the metric used for exporting how fast we can retrieve the /health endpoint.
 	HealthDuration = promauto.NewHistogram(prometheus.HistogramOpts{
-		Namespace: plugin.Namespace,
-		Subsystem: "health",
-		Name:      "request_duration_seconds",
-		Buckets:   plugin.SlimTimeBuckets,
-		Help:      "Histogram of the time (in seconds) each request took.",
+		Namespace:                   plugin.Namespace,
+		Subsystem:                   "health",
+		Name:                        "request_duration_seconds",
+		Buckets:                     plugin.SlimTimeBuckets,
+		NativeHistogramBucketFactor: plugin.NativeHistogramBucketFactor,
+		Help:                        "Histogram of the time (in seconds) each request took.",
 	})
 	// HealthFailures is the metric used to count how many times the health request failed
 	HealthFailures = promauto.NewCounter(prometheus.CounterOpts{
diff --git a/plugin/kubernetes/metrics.go b/plugin/kubernetes/metrics.go
index d6927cd98..caebffad6 100644
--- a/plugin/kubernetes/metrics.go
+++ b/plugin/kubernetes/metrics.go
@@ -16,11 +16,12 @@ var (
 	// requestLatency measures K8s rest client requests latency grouped by verb and host.
 	requestLatency = promauto.NewHistogramVec(
 		prometheus.HistogramOpts{
-			Namespace: plugin.Namespace,
-			Subsystem: "kubernetes",
-			Name:      "rest_client_request_duration_seconds",
-			Help:      "Request latency in seconds. Broken down by verb and host.",
-			Buckets:   prometheus.DefBuckets,
+			Namespace:                   plugin.Namespace,
+			Subsystem:                   "kubernetes",
+			Name:                        "rest_client_request_duration_seconds",
+			Help:                        "Request latency in seconds. Broken down by verb and host.",
+			Buckets:                     prometheus.DefBuckets,
+			NativeHistogramBucketFactor: plugin.NativeHistogramBucketFactor,
 		},
 		[]string{"verb", "host"},
 	)
@@ -28,11 +29,12 @@ var (
 	// rateLimiterLatency measures K8s rest client rate limiter latency grouped by verb and host.
 	rateLimiterLatency = promauto.NewHistogramVec(
 		prometheus.HistogramOpts{
-			Namespace: plugin.Namespace,
-			Subsystem: "kubernetes",
-			Name:      "rest_client_rate_limiter_duration_seconds",
-			Help:      "Client side rate limiter latency in seconds. Broken down by verb and host.",
-			Buckets:   prometheus.DefBuckets,
+			Namespace:                   plugin.Namespace,
+			Subsystem:                   "kubernetes",
+			Name:                        "rest_client_rate_limiter_duration_seconds",
+			Help:                        "Client side rate limiter latency in seconds. Broken down by verb and host.",
+			Buckets:                     prometheus.DefBuckets,
+			NativeHistogramBucketFactor: plugin.NativeHistogramBucketFactor,
 		},
 		[]string{"verb", "host"},
 	)
diff --git a/plugin/kubernetes/object/metrics.go b/plugin/kubernetes/object/metrics.go
index f39744b8a..149648411 100644
--- a/plugin/kubernetes/object/metrics.go
+++ b/plugin/kubernetes/object/metrics.go
@@ -29,8 +29,9 @@ var (
 		Subsystem: "kubernetes",
 		Name:      "dns_programming_duration_seconds",
 		// From 1 millisecond to ~17 minutes.
-		Buckets: prometheus.ExponentialBuckets(0.001, 2, 20),
-		Help:    "Histogram of the time (in seconds) it took to program a dns instance.",
+		Buckets:                     prometheus.ExponentialBuckets(0.001, 2, 20),
+		NativeHistogramBucketFactor: plugin.NativeHistogramBucketFactor,
+		Help:                        "Histogram of the time (in seconds) it took to program a dns instance.",
 	}, []string{"service_kind"})
 
 	// DurationSinceFunc returns the duration elapsed since the given time.
diff --git a/plugin/metrics/vars/vars.go b/plugin/metrics/vars/vars.go
index 6de75c044..7b8078509 100644
--- a/plugin/metrics/vars/vars.go
+++ b/plugin/metrics/vars/vars.go
@@ -17,19 +17,21 @@ var (
 	}, []string{"server", "zone", "view", "proto", "family", "type"})
 
 	RequestDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
-		Namespace: plugin.Namespace,
-		Subsystem: subsystem,
-		Name:      "request_duration_seconds",
-		Buckets:   plugin.TimeBuckets,
-		Help:      "Histogram of the time (in seconds) each request took per zone.",
+		Namespace:                   plugin.Namespace,
+		Subsystem:                   subsystem,
+		Name:                        "request_duration_seconds",
+		Buckets:                     plugin.TimeBuckets,
+		NativeHistogramBucketFactor: plugin.NativeHistogramBucketFactor,
+		Help:                        "Histogram of the time (in seconds) each request took per zone.",
 	}, []string{"server", "zone", "view"})
 
 	RequestSize = promauto.NewHistogramVec(prometheus.HistogramOpts{
-		Namespace: plugin.Namespace,
-		Subsystem: subsystem,
-		Name:      "request_size_bytes",
-		Help:      "Size of the EDNS0 UDP buffer in bytes (64K for TCP) per zone and protocol.",
-		Buckets:   []float64{0, 100, 200, 300, 400, 511, 1023, 2047, 4095, 8291, 16e3, 32e3, 48e3, 64e3},
+		Namespace:                   plugin.Namespace,
+		Subsystem:                   subsystem,
+		Name:                        "request_size_bytes",
+		Help:                        "Size of the EDNS0 UDP buffer in bytes (64K for TCP) per zone and protocol.",
+		Buckets:                     []float64{0, 100, 200, 300, 400, 511, 1023, 2047, 4095, 8291, 16e3, 32e3, 48e3, 64e3},
+		NativeHistogramBucketFactor: plugin.NativeHistogramBucketFactor,
 	}, []string{"server", "zone", "view", "proto"})
 
 	RequestDo = promauto.NewCounterVec(prometheus.CounterOpts{
@@ -40,11 +42,12 @@ var (
 	}, []string{"server", "zone", "view"})
 
 	ResponseSize = promauto.NewHistogramVec(prometheus.HistogramOpts{
-		Namespace: plugin.Namespace,
-		Subsystem: subsystem,
-		Name:      "response_size_bytes",
-		Help:      "Size of the returned response in bytes.",
-		Buckets:   []float64{0, 100, 200, 300, 400, 511, 1023, 2047, 4095, 8291, 16e3, 32e3, 48e3, 64e3},
+		Namespace:                   plugin.Namespace,
+		Subsystem:                   subsystem,
+		Name:                        "response_size_bytes",
+		Help:                        "Size of the returned response in bytes.",
+		Buckets:                     []float64{0, 100, 200, 300, 400, 511, 1023, 2047, 4095, 8291, 16e3, 32e3, 48e3, 64e3},
+		NativeHistogramBucketFactor: plugin.NativeHistogramBucketFactor,
 	}, []string{"server", "zone", "view", "proto"})
 
 	ResponseRcode = promauto.NewCounterVec(prometheus.CounterOpts{
diff --git a/plugin/pkg/proxy/metrics.go b/plugin/pkg/proxy/metrics.go
index e4cae97c3..7def8b7ea 100644
--- a/plugin/pkg/proxy/metrics.go
+++ b/plugin/pkg/proxy/metrics.go
@@ -10,11 +10,12 @@ import (
 // Variables declared for monitoring.
 var (
 	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.",
+		Namespace:                   plugin.Namespace,
+		Subsystem:                   "proxy",
+		Name:                        "request_duration_seconds",
+		Buckets:                     plugin.TimeBuckets,
+		NativeHistogramBucketFactor: plugin.NativeHistogramBucketFactor,
+		Help:                        "Histogram of the time each request took.",
 	}, []string{"proxy_name", "to", "rcode"})
 
 	healthcheckFailureCount = promauto.NewCounterVec(prometheus.CounterOpts{
diff --git a/plugin/plugin.go b/plugin/plugin.go
index 51f5ba79c..ca5fe0100 100644
--- a/plugin/plugin.go
+++ b/plugin/plugin.go
@@ -108,5 +108,9 @@ var TimeBuckets = prometheus.ExponentialBuckets(0.00025, 2, 16) // from 0.25ms t
 // SlimTimeBuckets is low cardinality set of duration buckets.
 var SlimTimeBuckets = prometheus.ExponentialBuckets(0.00025, 10, 5) // from 0.25ms to 2.5 seconds
 
+// NativeHistogramBucketFactor controls the resolution of Prometheus native histogram buckets.
+// See: https://pkg.go.dev/github.com/prometheus/client_golang@v1.19.0/prometheus#section-readme
+var NativeHistogramBucketFactor = 1.05
+
 // ErrOnce is returned when a plugin doesn't support multiple setups per server.
 var ErrOnce = errors.New("this plugin can only be used once per Server Block")