Package org.opendaylight.controller.cluster.raft

Class RaftActor

java.lang.Object
org.apache.pekko.actor.AbstractActor
org.opendaylight.controller.cluster.common.actor.AbstractUntypedActor
org.opendaylight.controller.cluster.raft.RaftActor
All Implemented Interfaces:
Actor, ExecuteInSelfActor
Direct Known Subclasses:
Shard
public abstract class RaftActor extends AbstractUntypedActor
RaftActor encapsulates a state machine that needs to be kept synchronized in a cluster. It implements the RAFT algorithm as described in the paper In Search of an Understandable Consensus Algorithm

RaftActor has 3 states and each state has a certain behavior associated with it. A Raft actor can behave as,

  • A Leader
  • A Follower (or)
  • A Candidate

A RaftActor MUST be a Leader in order to accept requests from clients to change the state of it's encapsulated state machine. Once a RaftActor becomes a Leader it is also responsible for ensuring that all followers ultimately have the same log and therefore the same state machine as itself.

The current behavior of a RaftActor determines how election for leadership is initiated and how peer RaftActors react to request for votes.

Each RaftActor also needs to know the current election term. It uses this information for a couple of things. One is to simply figure out who it voted for in the last election. Another is to figure out if the message it received to update it's state is stale.

The RaftActor uses akka-persistence to store it's replicated log. Furthermore through it's behaviors a Raft Actor determines

  • when a log entry should be persisted
  • when a log entry should be applied to the state machine (and)
  • when a snapshot should be saved

  • Constructor Details

  • Method Details

    • memberId

      public final @NonNull String memberId()
      Return the unique member name of this actor.
      Returns:
      The member name

    • getSender

      @Deprecated(since="11.0.0", forRemoval=true) public final ActorRef getSender()
      Deprecated, for removal: This API element is subject to removal in a future version.
      Overrides:
      getSender in class AbstractActor

    • preStart

      public void preStart() throws Exception
      Specified by:
      preStart in interface Actor
      Overrides:
      preStart in class AbstractActor
      Throws:
      Exception

    • postStop

      public void postStop() throws Exception
      Specified by:
      postStop in interface Actor
      Overrides:
      postStop in class AbstractActor
      Throws:
      Exception

    • overridePekkoRecoveredLog

      @NonNullByDefault protected ReplicatedLog overridePekkoRecoveredLog(ReplicatedLog recoveredLog)

    • handleNonRaftCommand

      protected void handleNonRaftCommand(Object message)
      Method exposed for subclasses to plug-in their logic. This method is invoked by handleReceive(Object) for messages which are not handled by this class. Subclasses overriding this class should fall back to this implementation for messages which they do not handle
      Parameters:
      message - Incoming command message

    • handleReceive

      protected final void handleReceive(Object message)
      Description copied from class: AbstractUntypedActor
      Receive and handle an incoming message. If the implementation does not handle this particular message, it should call AbstractUntypedActor.ignoreMessage(Object) or AbstractUntypedActor.unknownMessage(Object).
      Specified by:
      handleReceive in class AbstractUntypedActor
      Parameters:
      message - the incoming message

    • handleCommandImpl

      @Deprecated protected void handleCommandImpl(@NonNull Object message)
      Deprecated.
      This method is not final for testing purposes. DO NOT OVERRIDE IT, override handleNonRaftCommand(Object) instead.
      Handles a message.

    • newOnDemandRaftStateBuilder

      protected @NonNull OnDemandRaftState.AbstractBuilder<?,?> newOnDemandRaftStateBuilder()

    • applyCommand

      @NonNullByDefault protected abstract void applyCommand(@Nullable Identifier identifier, StateCommand command)
      Apply a StateCommand to update the actor's state.
      Parameters:
      identifier - The identifier of the persisted data. This is also the same identifier that was passed to submitCommand(Identifier, AbstractStateCommand, boolean) by the derived actor. May be null when the RaftActor is behaving as a follower or during recovery
      command - the StateCommand to apply

    • wrapLeaderStateChanged

      @NonNullByDefault protected LeaderStateChanged wrapLeaderStateChanged(LeaderStateChanged change)

    • submitCommand

      @NonNullByDefault public final void submitCommand(Identifier identifier, AbstractStateCommand command, boolean batchHint)
      Request a StateCommand to be applied to the finite state machine. Once consensus is reached, applyCommand(Identifier, StateCommand) will be called with matching arguments.
      Parameters:
      identifier - optional identifier to report back
      command - the command

    • getCurrentBehavior

      protected final RaftActorBehavior getCurrentBehavior()

    • isLeader

      protected boolean isLeader()
      Derived actors can call the isLeader method to check if the current RaftActor is the Leader or not.
      Returns:
      true it this RaftActor is a Leader false otherwise

    • isLeaderActive

      protected final boolean isLeaderActive()

    • isLeadershipTransferInProgress

      protected boolean isLeadershipTransferInProgress()

    • getLeader

      protected final @Nullable ActorSelection getLeader()
      Derived actor can call getLeader if they need a reference to the Leader. This would be useful for example in forwarding a request to an actor which is the leader.
      Returns:
      A reference to the leader if known, null otherwise

    • getLeaderId

      protected final String getLeaderId()
      Returns the id of the current leader.
      Returns:
      the current leader's id

    • getRaftState

      protected final RaftRole getRaftState()

    • getRaftActorContext

      public final RaftActorContext getRaftActorContext()

    • updateConfigParams

      protected void updateConfigParams(ConfigParams configParams)

    • isRecoveryApplicable

      public final boolean isRecoveryApplicable()

    • persistence

      @NonNullByDefault protected final PersistenceProvider persistence()

    • setPersistence

      protected final void setPersistence(boolean persistent)

    • setPeerAddress

      protected void setPeerAddress(String peerId, String peerAddress)
      setPeerAddress sets the address of a known peer at a later time.

      This is to account for situations where a we know that a peer exists but we do not know an address up-front. This may also be used in situations where a known peer starts off in a different location and we need to change it's address

      Note that if the peerId does not match the list of peers passed to this actor during construction an IllegalStateException will be thrown.

    • recoveryObserver

      protected @NonNull RecoveryObserver recoveryObserver()

    • getRaftActorRecoveryCohort

      protected abstract @NonNull RaftActorRecoveryCohort getRaftActorRecoveryCohort()
      Returns the RaftActorRecoveryCohort to participate in persistence recovery.

    • getRestoreFromSnapshot

      protected abstract @Nullable Snapshot getRestoreFromSnapshot()
      Returns the snapshot to restore from on recovery.
      Returns:
      the snapshot or null if there's no snapshot to restore

    • onRecoveryComplete

      protected abstract void onRecoveryComplete()
      This method is called when recovery is complete.

    • getRaftActorSnapshotCohort

      protected abstract @NonNull RaftActorSnapshotCohort<?> getRaftActorSnapshotCohort()
      Returns the RaftActorSnapshotCohort to participate in snapshot captures.

    • onStateChanged

      protected abstract void onStateChanged()
      This method will be called by the RaftActor when the state of the RaftActor changes. The derived actor can then use methods like isLeader or getLeader to do something useful

    • roleChangeNotifier

      protected abstract @Nullable ActorRef roleChangeNotifier()
      Notifier Actor for this RaftActor to notify when a role change happens.
      Returns:
      ActorRef - ActorRef of the notifier or null if none.

    • onVotingStateChangeComplete

      protected void onVotingStateChangeComplete()
      This method is called on the leader when a voting change operation completes.

    • pauseLeader

      protected void pauseLeader(Runnable operation)
      This method is called prior to operations such as leadership transfer and actor shutdown when the leader must pause or stop its duties. This method allows derived classes to gracefully pause or finish current work prior to performing the operation. On completion of any work, the run method must be called on the given Runnable to proceed with the given operation. Important: the run method must be called on this actor's thread dispatcher as as it modifies internal state.

      The default implementation immediately runs the operation.

      Parameters:
      operation - the operation to run

    • unpauseLeader

      protected void unpauseLeader()
      This method is invoked when the actions hooked to the leader becoming paused failed to execute and the leader should resume normal operations.

      Note this method can be invoked even before the operation supplied to pauseLeader(Runnable) is invoked.

    • onLeaderChanged

      protected void onLeaderChanged(String oldLeader, String newLeader)