metrics: add Prometheus metrics

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I13becfd5a309cc2e24579244d88343a56a6a6964

internal/metrics/metrics.go

@@ -0,0 +1,61 @@
+package metrics
+
+import "github.com/prometheus/client_golang/prometheus"
+
+var (
+	// Narinfo requests served from the route cache.
+	NarinfoCacheHits = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "ncro_narinfo_cache_hits_total",
+		Help: "Narinfo requests served from route cache.",
+	})
+
+	// Narinfo requests that required an upstream race.
+	NarinfoCacheMisses = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "ncro_narinfo_cache_misses_total",
+		Help: "Narinfo requests requiring upstream race.",
+	})
+
+	// Narinfo requests by HTTP status code.
+	NarinfoRequests = prometheus.NewCounterVec(prometheus.CounterOpts{
+		Name: "ncro_narinfo_requests_total",
+		Help: "Narinfo requests by status.",
+	}, []string{"status"})
+
+	// NAR streaming requests.
+	NARRequests = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "ncro_nar_requests_total",
+		Help: "NAR streaming requests.",
+	})
+
+	// Times each upstream won the narinfo race.
+	UpstreamRaceWins = prometheus.NewCounterVec(prometheus.CounterOpts{
+		Name: "ncro_upstream_race_wins_total",
+		Help: "Times each upstream won the narinfo race.",
+	}, []string{"upstream"})
+
+	// Current number of route entries in SQLite.
+	RouteEntries = prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "ncro_route_entries",
+		Help: "Current number of route entries in SQLite.",
+	})
+
+	// Upstream narinfo race latency in seconds.
+	UpstreamLatency = prometheus.NewHistogramVec(prometheus.HistogramOpts{
+		Name:    "ncro_upstream_latency_seconds",
+		Help:    "Upstream narinfo race latency.",
+		Buckets: prometheus.DefBuckets,
+	}, []string{"upstream"})
+)
+
+// Registers all metrics with reg.
+func Register(reg prometheus.Registerer) {
+	reg.MustRegister(
+		NarinfoCacheHits,
+		NarinfoCacheMisses,
+		NarinfoRequests,
+		NARRequests,
+		UpstreamRaceWins,
+		RouteEntries,
+		UpstreamLatency,
+	)
+}