feat(exporter): add prometheus exporter for cache, database & webserver stats

internal/exporter/metrics.go

@@ -0,0 +1,175 @@
+package exporter
+
+import (
+	"log"
+	"time"
+
+	"git.ar21.de/yolokube/country-geo-locations/internal/database"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const (
+	namespace      string = "country_geo_locations"
+	cacheSubsystem string = "cache"
+	dbSubsystem    string = "db"
+
+	metricLabelCacheTTL          string = "ttl"
+	metricLabelCurrentlyCached   string = "currently_cached"
+	metricLabelDatabaseTimestamp string = "timestamp"
+	metricLabelDatabaseReady     string = "ready"
+	metricLabelRequestsTotal     string = "requests_total"
+	metricLabelRequestLatency    string = "request_latency"
+)
+
+type Metrics struct {
+	metricCacheTTL          *prometheus.Desc
+	metricCurrentlyCached   *prometheus.Desc
+	metricDatabaseTimestamp *prometheus.Desc
+	metricDatabaseReady     *prometheus.Desc
+	metricRequestsTotal     *prometheus.Desc
+	metricRequestLatency    *prometheus.Desc
+}
+
+func NewMetrics() *Metrics {
+	return &Metrics{
+		metricCacheTTL: prometheus.NewDesc(
+			prometheus.BuildFQName(
+				namespace,
+				cacheSubsystem,
+				metricLabelCacheTTL,
+			),
+			"Duration for cached requests",
+			nil,
+			nil,
+		),
+		metricCurrentlyCached: prometheus.NewDesc(
+			prometheus.BuildFQName(
+				namespace,
+				cacheSubsystem,
+				metricLabelCurrentlyCached,
+			),
+			"Number of cached entries",
+			nil,
+			nil,
+		),
+		metricDatabaseTimestamp: prometheus.NewDesc(
+			prometheus.BuildFQName(
+				namespace,
+				dbSubsystem,
+				metricLabelDatabaseTimestamp,
+			),
+			"Timestamp of the CSV file",
+			[]string{metricLabelDatabaseTimestamp},
+			nil,
+		),
+		metricDatabaseReady: prometheus.NewDesc(
+			prometheus.BuildFQName(
+				namespace,
+				dbSubsystem,
+				metricLabelDatabaseReady,
+			),
+			"Ready status of the database",
+			nil,
+			nil,
+		),
+		metricRequestsTotal: prometheus.NewDesc(
+			prometheus.BuildFQName(
+				namespace,
+				"",
+				metricLabelRequestsTotal,
+			),
+			"Counter for total requests",
+			nil,
+			nil,
+		),
+		metricRequestLatency: prometheus.NewDesc(
+			prometheus.BuildFQName(
+				namespace,
+				"",
+				metricLabelRequestLatency,
+			),
+			"Latency statistics for requests",
+			nil,
+			nil,
+		),
+	}
+}
+
+func (m *Metrics) collectCacheTTLMetric(ch chan<- prometheus.Metric, ttl float64) {
+	ch <- prometheus.MustNewConstMetric(
+		m.metricCacheTTL,
+		prometheus.GaugeValue,
+		ttl,
+	)
+}
+
+func (m *Metrics) collectCurrentlyCachedMetric(ch chan<- prometheus.Metric, count float64) {
+	ch <- prometheus.MustNewConstMetric(
+		m.metricCurrentlyCached,
+		prometheus.GaugeValue,
+		count,
+	)
+}
+
+func (m *Metrics) collectDatabaseTimestampMetric(ch chan<- prometheus.Metric, db *database.Database) {
+	timestamp, err := db.Timestamp()
+	if err == nil {
+		ch <- prometheus.MustNewConstMetric(
+			m.metricDatabaseTimestamp,
+			prometheus.GaugeValue,
+			float64(timestamp.Unix()),
+			timestamp.String(),
+		)
+	} else {
+		log.Printf("failed to read file timestamp: %v\n", err)
+	}
+}
+
+func (m *Metrics) collectDatabaseReadyMetric(ch chan<- prometheus.Metric, ready bool) {
+	var dbReady uint8
+	if ready {
+		dbReady = 1
+	}
+
+	ch <- prometheus.MustNewConstMetric(
+		m.metricDatabaseReady,
+		prometheus.GaugeValue,
+		float64(dbReady),
+	)
+}
+
+func (m *Metrics) collectReqeustDataMetrics(ch chan<- prometheus.Metric, queue *RequestDataQueue) {
+	var (
+		count uint64
+		sum   float64
+	)
+	buckets := make(map[float64]uint64)
+	bucketBounds := prometheus.DefBuckets
+
+	data := queue.ConsumeAll()
+	for _, r := range data {
+		latency := r.Latency.Seconds()
+		sum += latency
+		count++
+
+		for _, bound := range bucketBounds {
+			if latency <= bound {
+				buckets[bound]++
+			}
+		}
+	}
+
+	ch <- prometheus.MustNewConstMetric(
+		m.metricRequestsTotal,
+		prometheus.CounterValue,
+		float64(len(data)),
+	)
+
+	ch <- prometheus.MustNewConstHistogramWithCreatedTimestamp(
+		m.metricRequestLatency,
+		count,
+		sum,
+		buckets,
+		time.Now(),
+	)
+}