Revert to original main-template without pod downtime (#6661)

Author: jjngx

internal/configs/configmaps.go

@@ -347,10 +347,14 @@ func ParseConfigMap(ctx context.Context, cfgm *v1.ConfigMap, nginxPlus bool, has
 
 	if mainTemplate, exists := cfgm.Data["main-template"]; exists {
 		cfgParams.MainTemplate = &mainTemplate
+	} else {
+		cfgParams.MainTemplate = nil
 	}
 
 	if ingressTemplate, exists := cfgm.Data["ingress-template"]; exists {
 		cfgParams.IngressTemplate = &ingressTemplate
+	} else {
+		cfgParams.IngressTemplate = nil
 	}
 
 	if virtualServerTemplate, exists := cfgm.Data["virtualserver-template"]; exists {

internal/configs/configurator.go

@@ -1310,11 +1310,15 @@ func (cnf *Configurator) UpdateConfig(cfgParams *ConfigParams, resources Extende
 		cfgParams.MainServerSSLDHParam = fileName
 	}
 
+	// Apply custom main-template defined in ConfigMap obj
 	if cfgParams.MainTemplate != nil {
 		err := cnf.templateExecutor.UpdateMainTemplate(cfgParams.MainTemplate)
 		if err != nil {
 			return allWarnings, fmt.Errorf("error when parsing the main template: %w", err)
 		}
+	} else {
+		// Reverse to default main template parsed at NIC startup.
+		cnf.templateExecutor.UseOriginalMainTemplate()
 	}
 
 	if cfgParams.IngressTemplate != nil {