Adding OpenTelemetry Metrics and Tracing

internal/telemetry/state_view.go

@@ -0,0 +1,106 @@
+package telemetry
+
+import (
+	"context"
+	"sync/atomic"
+	"time"
+
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/metric"
+)
+
+// StateView provides a read-only view for observable gauges.
+// Implementations must be concurrency-safe and avoid blocking operations.
+// All methods should be fast and use RLocks where applicable.
+type StateView interface {
+	// ListSites returns a stable, low-cardinality list of site IDs to expose.
+	ListSites() []string
+	// Online returns whether the site is online.
+	Online(siteID string) (online bool, ok bool)
+	// LastHeartbeat returns the last heartbeat time for a site.
+	LastHeartbeat(siteID string) (t time.Time, ok bool)
+	// ActiveSessions returns the current number of active sessions for a site (across tunnels),
+	// or scoped to site if your model is site-scoped.
+	ActiveSessions(siteID string) (n int64, ok bool)
+}
+
+var (
+	stateView atomic.Value // of type StateView
+)
+
+// RegisterStateView sets the global StateView used by the default observable callback.
+func RegisterStateView(v StateView) {
+	stateView.Store(v)
+	// If instruments are registered, ensure a callback exists.
+	if v != nil {
+		SetObservableCallback(func(ctx context.Context, o metric.Observer) error {
+			if any := stateView.Load(); any != nil {
+				if sv, ok := any.(StateView); ok {
+					for _, siteID := range sv.ListSites() {
+						observeSiteOnlineFor(o, sv, siteID)
+						observeLastHeartbeatFor(o, sv, siteID)
+						observeSessionsFor(o, siteID, sv)
+					}
+				}
+			}
+			return nil
+		})
+	}
+}
+
+func observeSiteOnlineFor(o metric.Observer, sv StateView, siteID string) {
+	if online, ok := sv.Online(siteID); ok {
+		val := int64(0)
+		if online {
+			val = 1
+		}
+		o.ObserveInt64(mSiteOnline, val, metric.WithAttributes(
+			attribute.String("site_id", siteID),
+		))
+	}
+}
+
+func observeLastHeartbeatFor(o metric.Observer, sv StateView, siteID string) {
+	if t, ok := sv.LastHeartbeat(siteID); ok {
+		ts := float64(t.UnixNano()) / 1e9
+		o.ObserveFloat64(mSiteLastHeartbeat, ts, metric.WithAttributes(
+			attribute.String("site_id", siteID),
+		))
+	}
+}
+
+func observeSessionsFor(o metric.Observer, siteID string, any interface{}) {
+	if tm, ok := any.(interface{ SessionsByTunnel() map[string]int64 }); ok {
+		sessions := tm.SessionsByTunnel()
+		// If tunnel_id labels are enabled, preserve existing per-tunnel observations
+		if ShouldIncludeTunnelID() {
+			for tid, n := range sessions {
+				attrs := []attribute.KeyValue{
+					attribute.String("site_id", siteID),
+				}
+				if tid != "" {
+					attrs = append(attrs, attribute.String("tunnel_id", tid))
+				}
+				o.ObserveInt64(mTunnelSessions, n, metric.WithAttributes(attrs...))
+			}
+			return
+		}
+		// When tunnel_id is disabled, collapse per-tunnel counts into a single site-level value
+		var total int64
+		for _, n := range sessions {
+			total += n
+		}
+		// If there are no per-tunnel entries, fall back to ActiveSessions() if available
+		if total == 0 {
+			if svAny := stateView.Load(); svAny != nil {
+				if sv, ok := svAny.(StateView); ok {
+					if n, ok2 := sv.ActiveSessions(siteID); ok2 {
+						total = n
+					}
+				}
+			}
+		}
+		o.ObserveInt64(mTunnelSessions, total, metric.WithAttributes(attribute.String("site_id", siteID)))
+		return
+	}
+}