@Transition(to = "OFFLINE", from = "STANDBY")
  public void onBecomeOfflineFromStandby(Message message, NotificationContext context) {
    logger.info("Partition {} in resource {} is becoming OFFLINE from STANDBY", message.getPartitionName(),
        message.getResourceName());
  }
A default LeaderStandby {@link StateModel} to use when the Ambry participants (datanodes) register to Helix. The
methods are callbacks that get called within a participant whenever partition's state changes in Helix. For now
these are no-ops.

In the critical path of puts and gets, there are no leader replicas in Ambry. Every replica can serve reads and
writes. However, going forward, it is useful to have one of the replicas chosen as a LEADER for purposes such as
replication.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/DefaultLeaderStandbyStateModel.java