code: func NewMetricsClient(api APIType, registry *prometheus.Registry) MetricsClient {
  	switch api {
  	case DockerAPI:
  		return NewGenericMetricsClient(DockerSubsystem, registry)
  	case TaskEngine:
  		return NewGenericMetricsClient(TaskEngineSubsystem, registry)
  	case StateManager:
  		return NewGenericMetricsClient(StateManagerSubsystem, registry)
  	case ECSClient:
  		return NewGenericMetricsClient(ECSClientSubsystem, registry)
  	default:
  		seelog.Error("Unmanaged MetricsClient cannot be created.")
  		return nil
  	}
  }
docs: // A factory method that enables various MetricsClients to be created.