telemetry: Fix atomic.Pointer initialisation responsibility

Return `atomic.pointer`, so that initialisation is not the responsibility of
another package.

cmd/icingadb/main.go

@@ -101,6 +101,7 @@ func run() int {
 	// the heartbeat is not read while HA gets stuck when updating the instance table.
 	var heartbeat *icingaredis.Heartbeat
 	var ha *icingadb.HA
+	var telemetrySyncStats *atomic.Pointer[telemetry.SuccessfulSync]
 	{
 		rc, err := cmd.Redis(logs.GetChildLogger("redis"))
 		if err != nil {
@@ -116,8 +117,7 @@ func run() int {
 		ha = icingadb.NewHA(ctx, db, heartbeat, logs.GetChildLogger("high-availability"))
 
 		telemetryLogger := logs.GetChildLogger("telemetry")
-		telemetry.LastSuccessfulSync.Store(&telemetry.SuccessfulSync{})
-		telemetry.StartHeartbeat(ctx, rc, telemetryLogger, ha, heartbeat)
+		telemetrySyncStats = telemetry.StartHeartbeat(ctx, rc, telemetryLogger, ha, heartbeat)
 		telemetry.WriteStats(ctx, rc, telemetryLogger)
 	}
 	// Closing ha on exit ensures that this instance retracts its heartbeat
@@ -251,7 +251,7 @@ func run() int {
 							logger := logs.GetChildLogger("config-sync")
 
 							if synctx.Err() == nil {
-								telemetry.LastSuccessfulSync.Store(&telemetry.SuccessfulSync{
+								telemetrySyncStats.Store(&telemetry.SuccessfulSync{
 									FinishMilli:   syncEnd.UnixMilli(),
 									DurationMilli: elapsed.Milliseconds(),
 								})

pkg/icingaredis/telemetry/heartbeat.go

@@ -79,16 +79,17 @@ func GetCurrentDbConnErr() (string, int64) {
 // OngoingSyncStartMilli is to be updated by the main() function.
 var OngoingSyncStartMilli int64
 
-// LastSuccessfulSync is to be updated by the main() function.
-var LastSuccessfulSync atomic.Pointer[SuccessfulSync]
-
 var boolToStr = map[bool]string{false: "0", true: "1"}
 var startTime = time.Now().UnixMilli()
 
 // StartHeartbeat periodically writes heartbeats to Redis for being monitored by Icinga 2.
+// It returns an atomic pointer to SuccessfulSync,
+// which contains synchronisation statistics that the caller should update.
 func StartHeartbeat(
 	ctx context.Context, client *redis.Client, logger *logging.Logger, ha ha, heartbeat *icingaredis.Heartbeat,
-) {
+) *atomic.Pointer[SuccessfulSync] {
+	var syncStats atomic.Pointer[SuccessfulSync]
+	syncStats.Store(&SuccessfulSync{})
 	goMetrics := NewGoMetrics()
 
 	const interval = time.Second
@@ -100,7 +101,7 @@ func StartHeartbeat(
 		heartbeat := heartbeat.LastReceived()
 		responsibleTsMilli, responsible, otherResponsible := ha.State()
 		ongoingSyncStart := atomic.LoadInt64(&OngoingSyncStartMilli)
-		lastSync := LastSuccessfulSync.Load()
+		lastSync := syncStats.Load()
 		dbConnErr, dbConnErrSinceMilli := GetCurrentDbConnErr()
 		now := time.Now()
 
@@ -144,6 +145,8 @@ func StartHeartbeat(
 			silenceUntil = time.Time{}
 		}
 	})
+
+	return &syncStats
 }
 
 type goMetrics struct {