code: public Resource getTotalUsedResources() {
      return getInstances().stream()
          .map(PackingPlan.InstancePlan::getResource)
          .reduce(Resource.EMPTY_RESOURCE, Resource::plus)
          .plus(getPadding());
    }
docs: Computes the used resources of the container by taking into account the resources
  allocated for each instance.
  
  @return a Resource object that describes the used CPU, RAM and disk in the container.