private StateModelDefinition getStateModelDefinition(String stateModelDefName) {
    StateModelDefinition stateModelDefinition;
    switch (stateModelDefName) {
      case ClusterMapConfig.OLD_STATE_MODEL_DEF:
        stateModelDefinition = LeaderStandbySMD.build();
        break;
      case ClusterMapConfig.AMBRY_STATE_MODEL_DEF:
        stateModelDefinition = AmbryStateModelDefinition.getDefinition();
        break;
      default:
        throw new IllegalArgumentException("Unsupported state model def: " + stateModelDefName);
    }
    return stateModelDefinition;
  }
Get state model definition based on given name.
@param stateModelDefName the name of state model definition that would be employed by Ambry cluster.
@return {@link StateModelDefinition}
ambry-clustermap/src/main/java/com/github/ambry/clustermap/HelixBootstrapUpgradeUtil.java