| CustomCodeCallbackHandler | Callback interface to running custom code on Helix participant manager The custom code will be triggered on user specified cluster changes |
| StateMachineEngine | Helix participant uses this class to register/remove state model factory State model factory creates state model that handles state transition messages |
| CustomCodeInvoker | |
| DistClusterControllerElection | |
| DistClusterControllerStateModel | |
| DistClusterControllerStateModelFactory | |
| GenericLeaderStandbyModel | |
| GenericLeaderStandbyStateModelFactory | |
| HelixCustomCodeRunner | This provides the ability for users to run a custom code in exactly one process using a LeaderStandBy state model. |
| HelixStateMachineEngine |