code: func (s *Server) checkConfigExistence(tx store.Tx, spec *api.ServiceSpec) error {
  	container := spec.Task.GetContainer()
  	if container == nil {
  		return nil
  	}
  
  	var failedConfigs []string
  	for _, configRef := range container.Configs {
  		config := store.GetConfig(tx, configRef.ConfigID)
  		// Check to see if the config exists and configRef.ConfigName matches the actual configName
  		if config == nil || config.Spec.Annotations.Name != configRef.ConfigName {
  			failedConfigs = append(failedConfigs, configRef.ConfigName)
  		}
  	}
  
  	if len(failedConfigs) > 0 {
  		configStr := "configs"
  		if len(failedConfigs) == 1 {
  			configStr = "config"
  		}
  
  		return status.Errorf(codes.InvalidArgument, "%s not found: %v", configStr, strings.Join(failedConfigs, ", "))
  
  	}
  
  	return nil
  }
docs: // checkConfigExistence finds if the config exists