List<String> getStandbyList(String activeContainerId) {
    return this.standbyContainerConstraints.get(activeContainerId);
  }
Fetches a list of standby container for an active container
@param activeContainerId logical id of the container ex: 0,1,2
@return list of standby containers ex: for active container 0: {0-0, 0-1}
samza-core/src/main/java/org/apache/samza/clustermanager/StandbyContainerManager.java