code: func (a *HistoricalApi) freeContainerMetrics(request *restful.Request, response *restful.Response) {
  	key := core.HistoricalKey{
  		ObjectType:    core.MetricSetTypeSystemContainer,
  		NodeName:      request.PathParameter("node-name"),
  		ContainerName: request.PathParameter("container-name"),
  	}
  	a.processMetricRequest(key, request, response)
  }
docs: // freeContainerMetrics returns a metric timeseries for a metric of the Container entity.
  // freeContainerMetrics addresses only free containers.