BUG: Fix data race between configureAPI() and reloadConfigurationFile()

ConfigWatcher() issuing reloadConfigurationFile() will data race with
ConfigureAPI(), reloadConfigurationFile() doing unsafe write and
configureAPI() doing unsafe read. Patch adds global clientMutex for
safely handling client changes.

Author: dkorunic

configure_data_plane.go

@@ -76,6 +76,7 @@ var (
 	AppLogger             *log.Logger
 	AccLogger             *log.Logger
 	serverStartedCallback func()
+	clientMutex           sync.Mutex
 )
 
 func SetServerStartedCallback(callFunc func()) {
@@ -110,6 +111,9 @@ func configureFlags(api *operations.DataPlaneAPI) {
 }
 
 func configureAPI(api *operations.DataPlaneAPI) http.Handler {
+	clientMutex.Lock()
+	defer clientMutex.Unlock()
+
 	cfg := dataplaneapi_config.Get()
 
 	haproxyOptions := cfg.HAProxy
@@ -954,6 +958,8 @@ func reloadConfigurationFile(client *client_native.HAProxyClient, haproxyOptions
 		log.Fatalf(err.Error())
 	}
 	log.Info("Rereading Configuration Files")
+	clientMutex.Lock()
+	defer clientMutex.Unlock()
 	client.Configuration = confClient
 }