Add Prometheus metrics to redisbp

Add a Prometheus exporter interface implementation to the redisbp
`NewMonitoredClient()`.

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

Author: SuperQ

redis/db/redisbp/monitored_client.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/go-redis/redis/v8"
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/reddit/baseplate.go/metricsbp"
 )
 
@@ -25,6 +26,13 @@ type PoolStatser interface {
 func NewMonitoredClient(name string, opt *redis.Options) *redis.Client {
 	client := redis.NewClient(opt)
 	client.AddHook(SpanHook{ClientName: name})
+
+	if err := prometheus.Register(newExporter(client, name)); err != nil {
+		// prometheus.Register should never fail because
+		// exporter.Describe is a no-op, but just in case.
+		return nil
+	}
+
 	return client
 }
 
@@ -33,6 +41,13 @@ func NewMonitoredClient(name string, opt *redis.Options) *redis.Client {
 func NewMonitoredFailoverClient(name string, opt *redis.FailoverOptions) *redis.Client {
 	client := redis.NewFailoverClient(opt)
 	client.AddHook(SpanHook{ClientName: name})
+
+	if err := prometheus.Register(newExporter(client, name)); err != nil {
+		// prometheus.Register should never fail because
+		// exporter.Describe is a no-op, but just in case.
+		return nil
+	}
+
 	return client
 }
 
@@ -78,6 +93,12 @@ func NewMonitoredClusterClient(name string, opt *redis.ClusterOptions) *ClusterC
 	client := redis.NewClusterClient(opt)
 	client.AddHook(SpanHook{ClientName: name})
 
+	if err := prometheus.Register(newExporter(client, name)); err != nil {
+		// prometheus.Register should never fail because
+		// exporter.Describe is a no-op, but just in case.
+		return nil
+	}
+
 	return &ClusterClient{client}
 }
 

redis/db/redisbp/prometheus.go

@@ -0,0 +1,128 @@
+package redisbp
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const (
+	promNamespace = "redisbp"
+	subsystemPool = "pool"
+
+	nameLabel = "pool"
+)
+
+// exporter provides an interface for Prometheus metrics.
+type exporter struct {
+	client PoolStatser
+	name   string
+
+	poolHitsCounterDesc     *prometheus.Desc
+	poolMissesCounterDesc   *prometheus.Desc
+	poolTimeoutsCounterDesc *prometheus.Desc
+	totalConnectionsDesc    *prometheus.Desc
+	idleConnectionsDesc     *prometheus.Desc
+	staleConnectionsDesc    *prometheus.Desc
+}
+
+func newExporter(client PoolStatser, name string) *exporter {
+	labels := []string{
+		nameLabel,
+	}
+
+	return &exporter{
+		client: client,
+		name:   name,
+
+		// Upstream docs: https://pkg.go.dev/github.com/go-redis/redis/v8/internal/pool#Stats
+
+		// Counters.
+		poolHitsCounterDesc: prometheus.NewDesc(
+			prometheus.BuildFQName(promNamespace, subsystemPool, "hits_total"),
+			"Number of times free connection was found in the pool",
+			labels,
+			nil,
+		),
+		poolMissesCounterDesc: prometheus.NewDesc(
+			prometheus.BuildFQName(promNamespace, subsystemPool, "misses_total"),
+			"Number of times free connection was NOT found in the pool",
+			labels,
+			nil,
+		),
+		poolTimeoutsCounterDesc: prometheus.NewDesc(
+			prometheus.BuildFQName(promNamespace, subsystemPool, "timeouts_total"),
+			"Number of times a wait timeout occurred",
+			labels,
+			nil,
+		),
+
+		// Gauges.
+		totalConnectionsDesc: prometheus.NewDesc(
+			prometheus.BuildFQName(promNamespace, subsystemPool, "connections"),
+			"Number of connections in this redisbp pool",
+			labels,
+			nil,
+		),
+		idleConnectionsDesc: prometheus.NewDesc(
+			prometheus.BuildFQName(promNamespace, subsystemPool, "idle_connections"),
+			"Number of idle connections in this redisbp pool",
+			labels,
+			nil,
+		),
+		staleConnectionsDesc: prometheus.NewDesc(
+			prometheus.BuildFQName(promNamespace, subsystemPool, "stale_connections"),
+			"Number of stale connections in this redisbp pool",
+			labels,
+			nil,
+		),
+	}
+}
+
+// Describe implements the prometheus.Collector interface.
+func (e *exporter) Describe(ch chan<- *prometheus.Desc) {
+	// All metrics are described dynamically.
+}
+
+// Collect implements prometheus.Collector.
+func (e *exporter) Collect(ch chan<- prometheus.Metric) {
+	stats := e.client.PoolStats()
+
+	// Counters.
+	ch <- prometheus.MustNewConstMetric(
+		e.poolHitsCounterDesc,
+		prometheus.CounterValue,
+		float64(stats.Hits),
+		e.name,
+	)
+	ch <- prometheus.MustNewConstMetric(
+		e.poolMissesCounterDesc,
+		prometheus.CounterValue,
+		float64(stats.Misses),
+		e.name,
+	)
+	ch <- prometheus.MustNewConstMetric(
+		e.poolTimeoutsCounterDesc,
+		prometheus.CounterValue,
+		float64(stats.Timeouts),
+		e.name,
+	)
+
+	// Gauges.
+	ch <- prometheus.MustNewConstMetric(
+		e.totalConnectionsDesc,
+		prometheus.GaugeValue,
+		float64(stats.TotalConns),
+		e.name,
+	)
+	ch <- prometheus.MustNewConstMetric(
+		e.idleConnectionsDesc,
+		prometheus.GaugeValue,
+		float64(stats.IdleConns),
+		e.name,
+	)
+	ch <- prometheus.MustNewConstMetric(
+		e.staleConnectionsDesc,
+		prometheus.GaugeValue,
+		float64(stats.StaleConns),
+		e.name,
+	)
+}

redis/db/redisbp/prometheus_test.go

@@ -0,0 +1,46 @@
+package redisbp
+
+import (
+	"sync"
+	"testing"
+
+	"github.com/go-redis/redis/v8"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+type fakeClient redis.Client
+
+// PoolStats returns connection pool stats.
+func (c fakeClient) PoolStats() *redis.PoolStats {
+	return &redis.PoolStats{
+		Hits:     1,
+		Misses:   2,
+		Timeouts: 3,
+
+		TotalConns: 4,
+		IdleConns:  5,
+		StaleConns: 6,
+	}
+}
+
+func TestRedisPoolExporter(t *testing.T) {
+	client := &fakeClient{}
+
+	exporter := newExporter(
+		client,
+		"test",
+	)
+	// No real test here, we just want to make sure that Collect call will not
+	// panic, which would happen if we have a label mismatch.
+	ch := make(chan prometheus.Metric)
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for range ch {
+		}
+	}()
+	exporter.Collect(ch)
+	close(ch)
+	wg.Wait()
+}