Change NatsMessenger to Singleton Init

cmd/cc-backend/main.go

@@ -216,10 +216,7 @@ func main() {
 
 	// Start NATS Messenger if Config exists
 	wg.Add(1)
-	nm, err := natsMessenger.New(config.Keys.Nats)
-	if err != nil {
-		log.Fatal("Error on NATS startup!")
-	}
+	nm := natsMessenger.GetNatsMessenger(config.Keys.Nats)
 	wg.Done()
 
 	// Start HTTP server

internal/natsMessenger/natsMessenger.go

@@ -12,6 +12,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"sync"
 	"time"
 
 	"github.com/ClusterCockpit/cc-backend/internal/importer"
@@ -31,9 +32,8 @@ type NatsMessenger struct {
 	jwtPubKey     ed25519.PublicKey
 }
 
-func New(config *schema.NatsConfig) (nm *NatsMessenger, err error) {
-	return SetupNatsMessenger(config)
-}
+var natsMessengerInstance *NatsMessenger
+var once sync.Once
 
 type DevNatsMessage struct {
 	Content string `json:"content"`
@@ -72,75 +72,71 @@ type ReceiveEventNatsRequest struct {
 	Value     *int64  `json:"value,omitempty" example:"150"`              // Optional Value Set for Evenr, eg powercap
 }
 
-// Check auth and setup listeners to channels
-
-// ns *server.Server, nc *nats.Conn, subs []*nats.Subscription, err error
-func SetupNatsMessenger(config *schema.NatsConfig) (nm *NatsMessenger, err error) {
+// Get Singleton
+func GetNatsMessenger(config *schema.NatsConfig) *NatsMessenger {
 	// Check if Config present
 	if config == nil {
 		log.Info("No NATS config found: Skip NATS init.")
-		return nil, nil
+		return nil
 	}
 
-	// Init Raw
-	nmr := NatsMessenger{
+	if natsMessengerInstance == nil {
+		once.Do(
+			func() {
+				// Raw Init
+				var err error
+				natsMessengerInstance = &NatsMessenger{
 					Server:        nil,
 					Connection:    nil,
 					Subscriptions: []*nats.Subscription{},
 					JobRepository: repository.GetJobRepository(),
 					jwtPubKey:     nil,
 				}
-
 				// Init JWT PubKey
 				pubKey := os.Getenv("JWT_PUBLIC_KEY")
 				if pubKey == "" {
 					log.Warn("environment variable 'JWT_PUBLIC_KEY' not set (token based authentication will not work for nats: abort setup)")
-		return nil, fmt.Errorf("environment variable 'JWT_PUBLIC_KEY' not set (token based authentication will not work for nats: abort nats setup)")
 				} else {
-		bytes, err := base64.StdEncoding.DecodeString(pubKey)
-		if err != nil {
+					if bytes, err := base64.StdEncoding.DecodeString(pubKey); err != nil {
 						log.Warn("Could not decode JWT public key")
-			return nil, err
+					} else {
+						natsMessengerInstance.jwtPubKey = ed25519.PublicKey(bytes)
 					}
-		nmr.jwtPubKey = ed25519.PublicKey(bytes)
 				}
 
 				// Start Nats Server
 				// Note: You can configure things like Host, Port, Authorization, and much more using server.Options.
 				opts := &server.Options{Port: config.Port}
-	nmr.Server, err = server.NewServer(opts)
-
-	if err != nil {
+				if natsMessengerInstance.Server, err = server.NewServer(opts); err != nil {
 					log.Error("nats server error on creation")
-		return nil, err
 				}
 
-	go nmr.Server.Start()
+				go natsMessengerInstance.Server.Start()
 
-	if !nmr.Server.ReadyForConnections(3 * time.Second) {
+				if !natsMessengerInstance.Server.ReadyForConnections(3 * time.Second) {
 					log.Error("nats server not ready for connection")
-		return nil, fmt.Errorf("nats server not ready for connection")
 				}
 
 				// Connect
 				var copts []nats.Option
-	nmr.Connection, err = nats.Connect(nmr.Server.ClientURL(), copts...)
-	if nmr.Connection == nil {
-		nmr.Server.Shutdown()
+				if natsMessengerInstance.Connection, err = nats.Connect(natsMessengerInstance.Server.ClientURL(), copts...); err != nil {
+					natsMessengerInstance.Server.Shutdown()
 					log.Error("nats connection could not be established: nats shut down")
-		return nil, err
 				}
 
 				// Subscribe
-	if err = nmr.setupSubscriptions(); err != nil {
+				if err = natsMessengerInstance.setupSubscriptions(); err != nil {
 					log.Error("error when subscribing to channels: nats shut down")
-		nmr.Connection.Close()
-		nmr.Server.Shutdown()
-		return nil, err
+					natsMessengerInstance.Connection.Close()
+					natsMessengerInstance.Server.Shutdown()
+				}
+			})
+		log.Infof("NATS server and subscriptions on port '%d' established\n", config.Port)
+	} else {
+		log.Infof("Single NatsMessenger instance already created on port '%d'\n", config.Port)
 	}
 
-	log.Infof("NATS server and subscriptions on port '%d' established\n", config.Port)
-	return &nmr, nil
+	return natsMessengerInstance
 }
 
 func (nm *NatsMessenger) StopNatsMessenger() {