Trace GC sweeps and (opt-in) health probes

Co-Authored-By: Claude <noreply@anthropic.com>

internal/health/engine.go

@@ -10,6 +10,9 @@ import (
 	"sync"
 	"time"
 
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/codes"
+	"go.opentelemetry.io/otel/trace"
 	apimeta "k8s.io/apimachinery/pkg/api/meta"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/types"
@@ -18,6 +21,7 @@ import (
 	logf "sigs.k8s.io/controller-runtime/pkg/log"
 
 	crawlv1alpha1 "gitea.home.hrajfrisbee.cz/kacerr/egress-proxies-operator/api/v1alpha1"
+	"gitea.home.hrajfrisbee.cz/kacerr/egress-proxies-operator/internal/tracing"
 )
 
 // Snapshot is the engine's current verdict for one proxy, read by the
@@ -99,6 +103,10 @@ type Engine struct {
 	// transition-only by design, so metrics are where high-frequency
 	// signal (true probe recency, every latency sample) lives.
 	Metrics ProbeMetrics
+	// TraceProbes emits one root span per probe (--trace-health-probes).
+	// Off by default: probes run about once per second per proxy and would
+	// dominate trace volume.
+	TraceProbes bool
 
 	probeFn func(context.Context, *url.URL, crawlv1alpha1.HealthCheckSpec, *tls.Config) probeResult
 
@@ -155,8 +163,7 @@ func (e *Engine) Start(ctx context.Context) error {
 				case <-ctx.Done():
 					return
 				case job := <-jobs:
-					res := e.probeFn(ctx, job.proxyURL, job.hc, e.ProbeTLSConfig)
-					e.record(job, res, time.Now())
+					e.record(job, e.runProbe(ctx, job), time.Now())
 				}
 			}
 		})
@@ -264,6 +271,29 @@ func newState(p *crawlv1alpha1.Proxy, now time.Time, interval time.Duration) *st
 	return st
 }
 
+// runProbe executes one probe, inside its own root span when TraceProbes is
+// on. The span ends before record folds the result (record stays ctx-free),
+// and the probe transport is deliberately uninstrumented — no traceparent
+// must ever leak through a proxy toward external targets.
+func (e *Engine) runProbe(ctx context.Context, job probeJob) probeResult {
+	if !e.TraceProbes {
+		return e.probeFn(ctx, job.proxyURL, job.hc, e.ProbeTLSConfig)
+	}
+	ctx, span := tracing.Start(ctx, "health.probe",
+		trace.WithSpanKind(trace.SpanKindClient),
+		trace.WithAttributes(attribute.String("proxy", job.key.String())))
+	defer span.End()
+	res := e.probeFn(ctx, job.proxyURL, job.hc, e.ProbeTLSConfig)
+	span.SetAttributes(
+		attribute.Bool("probe.ok", res.ok),
+		attribute.Int64("probe.latency_ms", res.latency.Milliseconds()),
+	)
+	if !res.ok {
+		span.SetStatus(codes.Error, res.err.Error())
+	}
+	return res
+}
+
 // record folds one probe result into the proxy's threshold state and emits
 // an event when the result is status-affecting: a first-ever verdict, a
 // threshold-crossing flip, or a material latency change (beyond