stats: Follow stats.interval on reload, interface gauges ride the capture loop (#1919)

interface_emit_test.go

@@ -3,7 +3,6 @@
 package nebula
 
 import (
-	"context"
 	"net/netip"
 	"testing"
 	"time"
@@ -18,11 +17,8 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-// Test_emitStats_primesGauges covers issue #907: a Prometheus scrape that
-// landed before the first ticker fire used to read 0 for the cert gauges.
-// emitStats now primes the gauges before entering the ticker loop. We assert
-// the gauge is zero before the first call and non-zero after.
-func Test_emitStats_primesGauges(t *testing.T) {
+// Priming before the first tick (issue #907) is Start's job, see TestStatsServer_Start_primes.
+func Test_statsEmitter_setsGauges(t *testing.T) {
 	defer metrics.DefaultRegistry.UnregisterAll()
 
 	l := test.NewLogger()
@@ -56,17 +52,12 @@ func Test_emitStats_primesGauges(t *testing.T) {
 	ifce.pki.cs.Store(cs)
 
 	ttlGauge := metrics.GetOrRegisterGauge("certificate.ttl_seconds", nil)
-	require.Zero(t, ttlGauge.Value(), "gauge should be zero before emitStats runs")
+	require.Zero(t, ttlGauge.Value(), "gauge should be zero before the emitter runs")
 
-	// Pre-cancel the context so emitStats returns after priming the gauges
-	// without ever reading from ticker.C. The one hour interval is just a
-	// belt-and-suspenders, the test does not expect the ticker to fire.
-	ctx, cancel := context.WithCancel(context.Background())
-	cancel()
-	ifce.emitStats(ctx, time.Hour)
+	ifce.statsEmitter()()
 
 	ttl := ttlGauge.Value()
-	assert.Positive(t, ttl, "ttl gauge should be primed by emitStats before its first tick")
+	assert.Positive(t, ttl, "ttl gauge should be set by one run of the emitter")
 	assert.LessOrEqual(t, ttl, int64(3600))
 	assert.Equal(t, int64(cert.Version1), metrics.GetOrRegisterGauge("certificate.initiating_version", nil).Value())
 	assert.Equal(t, int64(cert.Version1), metrics.GetOrRegisterGauge("certificate.max_version", nil).Value())