code: private PackingPlanBuilder getFFDAllocation(PackingPlanBuilder planBuilder)
        throws ConstraintViolationException {
      Map<String, Integer> parallelismMap = TopologyUtils.getComponentParallelism(topology);
      assignInstancesToContainers(planBuilder, parallelismMap);
      return planBuilder;
    }
docs: Get the instances' allocation based on the First Fit Decreasing algorithm
  
  @return Map &lt; containerId, list of InstanceId belonging to this container &gt;