opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/entityownership/EntityOwnershipShard.java

   1 /*
   2  * Copyright (c) 2015 Brocade Communications Systems, Inc. and others.  All rights reserved.
   3  *
   4  * This program and the accompanying materials are made available under the
   5  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
   6  * and is available at http://www.eclipse.org/legal/epl-v10.html
   7  */
   8 package org.opendaylight.controller.cluster.datastore.entityownership;
   9
  10 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.CANDIDATE_NAME_NODE_ID;
  11 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.CANDIDATE_NODE_ID;
  12 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_ID_NODE_ID;
  13 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_ID_QNAME;
  14 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_NODE_ID;
  15 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_OWNERS_PATH;
  16 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_OWNER_NODE_ID;
  17 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_OWNER_QNAME;
  18 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_TYPES_PATH;
  19 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_TYPE_NODE_ID;
  20 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_TYPE_QNAME;
  21 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.candidateNodeKey;
  22 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.candidatePath;
  23 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.entityOwnersWithCandidate;
  24
  25 import akka.actor.ActorRef;
  26 import akka.actor.ActorSelection;
  27 import akka.actor.Cancellable;
  28 import akka.cluster.Cluster;
  29 import akka.cluster.ClusterEvent.CurrentClusterState;
  30 import akka.cluster.Member;
  31 import akka.cluster.MemberStatus;
  32 import akka.pattern.Patterns;
  33 import com.google.common.base.Preconditions;
  34 import com.google.common.base.Strings;
  35 import com.google.common.collect.ImmutableList;
  36 import com.google.common.collect.ImmutableSet;
  37 import java.util.ArrayList;
  38 import java.util.Collection;
  39 import java.util.HashMap;
  40 import java.util.HashSet;
  41 import java.util.List;
  42 import java.util.Map;
  43 import java.util.Optional;
  44 import java.util.Set;
  45 import java.util.concurrent.TimeUnit;
  46 import org.opendaylight.controller.cluster.access.concepts.MemberName;
  47 import org.opendaylight.controller.cluster.datastore.DatastoreContext;
  48 import org.opendaylight.controller.cluster.datastore.Shard;
  49 import org.opendaylight.controller.cluster.datastore.entityownership.messages.CandidateAdded;
  50 import org.opendaylight.controller.cluster.datastore.entityownership.messages.CandidateRemoved;
  51 import org.opendaylight.controller.cluster.datastore.entityownership.messages.RegisterCandidateLocal;
  52 import org.opendaylight.controller.cluster.datastore.entityownership.messages.RegisterListenerLocal;
  53 import org.opendaylight.controller.cluster.datastore.entityownership.messages.RemoveAllCandidates;
  54 import org.opendaylight.controller.cluster.datastore.entityownership.messages.SelectOwner;
  55 import org.opendaylight.controller.cluster.datastore.entityownership.messages.UnregisterCandidateLocal;
  56 import org.opendaylight.controller.cluster.datastore.entityownership.messages.UnregisterListenerLocal;
  57 import org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy.EntityOwnerSelectionStrategy;
  58 import org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy.EntityOwnerSelectionStrategyConfig;
  59 import org.opendaylight.controller.cluster.datastore.identifiers.ShardIdentifier;
  60 import org.opendaylight.controller.cluster.datastore.messages.BatchedModifications;
  61 import org.opendaylight.controller.cluster.datastore.messages.PeerDown;
  62 import org.opendaylight.controller.cluster.datastore.messages.PeerUp;
  63 import org.opendaylight.controller.cluster.datastore.messages.SuccessReply;
  64 import org.opendaylight.controller.cluster.datastore.modification.DeleteModification;
  65 import org.opendaylight.controller.cluster.datastore.modification.MergeModification;
  66 import org.opendaylight.controller.cluster.datastore.modification.Modification;
  67 import org.opendaylight.controller.cluster.datastore.modification.WriteModification;
  68 import org.opendaylight.controller.cluster.raft.RaftState;
  69 import org.opendaylight.controller.cluster.raft.VotingState;
  70 import org.opendaylight.mdsal.eos.dom.api.DOMEntity;
  71 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
  72 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
  73 import org.opendaylight.yangtools.yang.data.api.schema.DataContainerChild;
  74 import org.opendaylight.yangtools.yang.data.api.schema.MapEntryNode;
  75 import org.opendaylight.yangtools.yang.data.api.schema.MapNode;
  76 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
  77 import org.opendaylight.yangtools.yang.data.impl.schema.ImmutableNodes;
  78 import scala.concurrent.Future;
  79 import scala.concurrent.duration.FiniteDuration;
  80
  81 /**
  82  * Special Shard for EntityOwnership.
  83  *
  84  * @author Thomas Pantelis
  85  */
  86 class EntityOwnershipShard extends Shard {
  87     private final MemberName localMemberName;
  88     private final EntityOwnershipShardCommitCoordinator commitCoordinator;
  89     private final EntityOwnershipListenerSupport listenerSupport;
  90     private final Set<MemberName> downPeerMemberNames = new HashSet<>();
  91     private final EntityOwnerSelectionStrategyConfig strategyConfig;
  92     private final Map<YangInstanceIdentifier, Cancellable> entityToScheduledOwnershipTask = new HashMap<>();
  93     private final EntityOwnershipStatistics entityOwnershipStatistics;
  94     private boolean removeAllInitialCandidates = true;
  95
  96     protected EntityOwnershipShard(final Builder builder) {
  97         super(builder);
  98         this.localMemberName = builder.localMemberName;
  99         this.commitCoordinator = new EntityOwnershipShardCommitCoordinator(builder.localMemberName, LOG);
 100         this.listenerSupport = new EntityOwnershipListenerSupport(getContext(), persistenceId());
 101         this.strategyConfig = builder.ownerSelectionStrategyConfig;
 102         this.entityOwnershipStatistics = new EntityOwnershipStatistics();
 103         this.entityOwnershipStatistics.init(getDataStore());
 104     }
 105
 106     private static DatastoreContext noPersistenceDatastoreContext(final DatastoreContext datastoreContext) {
 107         return DatastoreContext.newBuilderFrom(datastoreContext).persistent(false).build();
 108     }
 109
 110     @Override
 111     protected void onDatastoreContext(final DatastoreContext context) {
 112         super.onDatastoreContext(noPersistenceDatastoreContext(context));
 113     }
 114
 115     @Override
 116     protected void onRecoveryComplete() {
 117         super.onRecoveryComplete();
 118
 119         new CandidateListChangeListener(getSelf(), persistenceId()).init(getDataStore());
 120         new EntityOwnerChangeListener(localMemberName, listenerSupport).init(getDataStore());
 121     }
 122
 123     @Override
 124     public void handleNonRaftCommand(final Object message) {
 125         if (message instanceof RegisterCandidateLocal) {
 126             onRegisterCandidateLocal((RegisterCandidateLocal) message);
 127         } else if (message instanceof UnregisterCandidateLocal) {
 128             onUnregisterCandidateLocal((UnregisterCandidateLocal) message);
 129         } else if (message instanceof CandidateAdded) {
 130             onCandidateAdded((CandidateAdded) message);
 131         } else if (message instanceof CandidateRemoved) {
 132             onCandidateRemoved((CandidateRemoved) message);
 133         } else if (message instanceof PeerDown) {
 134             onPeerDown((PeerDown) message);
 135         } else if (message instanceof PeerUp) {
 136             onPeerUp((PeerUp) message);
 137         } else if (message instanceof RegisterListenerLocal) {
 138             onRegisterListenerLocal((RegisterListenerLocal) message);
 139         } else if (message instanceof UnregisterListenerLocal) {
 140             onUnregisterListenerLocal((UnregisterListenerLocal) message);
 141         } else if (message instanceof SelectOwner) {
 142             onSelectOwner((SelectOwner) message);
 143         } else if (message instanceof RemoveAllCandidates) {
 144             onRemoveAllCandidates((RemoveAllCandidates) message);
 145         } else if (!commitCoordinator.handleMessage(message, this)) {
 146             super.handleNonRaftCommand(message);
 147         }
 148     }
 149
 150     private void onRemoveAllCandidates(final RemoveAllCandidates message) {
 151         LOG.debug("{}: onRemoveAllCandidates: {}", persistenceId(), message);
 152
 153         removeCandidateFromEntities(message.getMemberName());
 154     }
 155
 156     private void onSelectOwner(final SelectOwner selectOwner) {
 157         LOG.debug("{}: onSelectOwner: {}", persistenceId(), selectOwner);
 158
 159         String currentOwner = getCurrentOwner(selectOwner.getEntityPath());
 160         if (Strings.isNullOrEmpty(currentOwner)) {
 161             writeNewOwner(selectOwner.getEntityPath(), newOwner(currentOwner, selectOwner.getAllCandidates(),
 162                     selectOwner.getOwnerSelectionStrategy()));
 163
 164             Cancellable cancellable = entityToScheduledOwnershipTask.get(selectOwner.getEntityPath());
 165             if (cancellable != null) {
 166                 if (!cancellable.isCancelled()) {
 167                     cancellable.cancel();
 168                 }
 169                 entityToScheduledOwnershipTask.remove(selectOwner.getEntityPath());
 170             }
 171         }
 172     }
 173
 174     private void onRegisterCandidateLocal(final RegisterCandidateLocal registerCandidate) {
 175         LOG.debug("{}: onRegisterCandidateLocal: {}", persistenceId(), registerCandidate);
 176
 177         NormalizedNode<?, ?> entityOwners = entityOwnersWithCandidate(registerCandidate.getEntity().getType(),
 178                 registerCandidate.getEntity().getIdentifier(), localMemberName.getName());
 179         commitCoordinator.commitModification(new MergeModification(ENTITY_OWNERS_PATH, entityOwners), this);
 180
 181         getSender().tell(SuccessReply.INSTANCE, getSelf());
 182     }
 183
 184     private void onUnregisterCandidateLocal(final UnregisterCandidateLocal unregisterCandidate) {
 185         LOG.debug("{}: onUnregisterCandidateLocal: {}", persistenceId(), unregisterCandidate);
 186
 187         DOMEntity entity = unregisterCandidate.getEntity();
 188         YangInstanceIdentifier candidatePath = candidatePath(entity.getType(), entity.getIdentifier(),
 189                 localMemberName.getName());
 190         commitCoordinator.commitModification(new DeleteModification(candidatePath), this);
 191
 192         getSender().tell(SuccessReply.INSTANCE, getSelf());
 193     }
 194
 195     private void onRegisterListenerLocal(final RegisterListenerLocal registerListener) {
 196         LOG.debug("{}: onRegisterListenerLocal: {}", persistenceId(), registerListener);
 197
 198         listenerSupport.addEntityOwnershipListener(registerListener.getEntityType(), registerListener.getListener());
 199
 200         getSender().tell(SuccessReply.INSTANCE, getSelf());
 201
 202         searchForEntities((entityTypeNode, entityNode) -> {
 203             Optional<DataContainerChild<?, ?>> possibleType = entityTypeNode.getChild(ENTITY_TYPE_NODE_ID);
 204             String entityType = possibleType.isPresent() ? possibleType.get().getValue().toString() : null;
 205             if (registerListener.getEntityType().equals(entityType)) {
 206                 final boolean hasOwner;
 207                 final boolean isOwner;
 208
 209                 Optional<DataContainerChild<?, ?>> possibleOwner = entityNode.getChild(ENTITY_OWNER_NODE_ID);
 210                 if (possibleOwner.isPresent()) {
 211                     isOwner = localMemberName.getName().equals(possibleOwner.get().getValue().toString());
 212                     hasOwner = true;
 213                 } else {
 214                     isOwner = false;
 215                     hasOwner = false;
 216                 }
 217
 218                 DOMEntity entity = new DOMEntity(entityType,
 219                     (YangInstanceIdentifier) entityNode.getChild(ENTITY_ID_NODE_ID).get().getValue());
 220
 221                 listenerSupport.notifyEntityOwnershipListener(entity, false, isOwner, hasOwner,
 222                     registerListener.getListener());
 223             }
 224         });
 225     }
 226
 227     private void onUnregisterListenerLocal(final UnregisterListenerLocal unregisterListener) {
 228         LOG.debug("{}: onUnregisterListenerLocal: {}", persistenceId(), unregisterListener);
 229
 230         listenerSupport.removeEntityOwnershipListener(unregisterListener.getEntityType(),
 231                 unregisterListener.getListener());
 232
 233         getSender().tell(SuccessReply.INSTANCE, getSelf());
 234     }
 235
 236     void tryCommitModifications(final BatchedModifications modifications) {
 237         if (isLeader()) {
 238             LOG.debug("{}: Committing BatchedModifications {} locally", persistenceId(),
 239                     modifications.getTransactionId());
 240
 241             // Note that it's possible the commit won't get consensus and will timeout and not be applied
 242             // to the state. However we don't need to retry it in that case b/c it will be committed to
 243             // the journal first and, once a majority of followers come back on line and it is replicated,
 244             // it will be applied at that point.
 245             handleBatchedModificationsLocal(modifications, self());
 246         } else {
 247             final ActorSelection leader = getLeader();
 248             if (leader != null) {
 249                 possiblyRemoveAllInitialCandidates(leader);
 250
 251                 LOG.debug("{}: Sending BatchedModifications {} to leader {}", persistenceId(),
 252                         modifications.getTransactionId(), leader);
 253
 254                 Future<Object> future = Patterns.ask(leader, modifications, TimeUnit.SECONDS.toMillis(
 255                         getDatastoreContext().getShardTransactionCommitTimeoutInSeconds()));
 256
 257                 Patterns.pipe(future, getContext().dispatcher()).pipeTo(getSelf(), ActorRef.noSender());
 258             }
 259         }
 260     }
 261
 262     void possiblyRemoveAllInitialCandidates(final ActorSelection leader) {
 263         // The following handles removing all candidates on startup when re-joining with a remote leader. When a
 264         // follower is detected as down, the leader will re-assign new owners to entities that were owned by the
 265         // down member but doesn't remove the down member as a candidate, as the down node may actually be isolated
 266         // and still running. Therefore on startup we send an initial message to the remote leader to remove any
 267         // potential stale candidates we had previously registered, as it's possible a candidate may not be
 268         // registered by a client in the new incarnation. We have to send the RemoveAllCandidates message prior to any
 269         // pending registrations.
 270         if (removeAllInitialCandidates && leader != null) {
 271             removeAllInitialCandidates = false;
 272             if (!isLeader()) {
 273                 LOG.debug("{} - got new leader {} on startup - sending RemoveAllCandidates", persistenceId(), leader);
 274
 275                 leader.tell(new RemoveAllCandidates(localMemberName), ActorRef.noSender());
 276             }
 277         }
 278     }
 279
 280     boolean hasLeader() {
 281         return getLeader() != null && (!isLeader() || isLeaderActive());
 282     }
 283
 284     /**
 285      * Determine if we are in jeopardy based on observed RAFT state.
 286      */
 287     private static boolean inJeopardy(final RaftState state) {
 288         switch (state) {
 289             case Candidate:
 290             case Follower:
 291             case Leader:
 292             case PreLeader:
 293                 return false;
 294             case IsolatedLeader:
 295                 return true;
 296             default:
 297                 throw new IllegalStateException("Unsupported RAFT state " + state);
 298         }
 299     }
 300
 301     private void notifyAllListeners() {
 302         searchForEntities((entityTypeNode, entityNode) -> {
 303             Optional<DataContainerChild<?, ?>> possibleType = entityTypeNode.getChild(ENTITY_TYPE_NODE_ID);
 304             if (possibleType.isPresent()) {
 305                 final boolean hasOwner;
 306                 final boolean isOwner;
 307
 308                 Optional<DataContainerChild<?, ?>> possibleOwner = entityNode.getChild(ENTITY_OWNER_NODE_ID);
 309                 if (possibleOwner.isPresent()) {
 310                     isOwner = localMemberName.getName().equals(possibleOwner.get().getValue().toString());
 311                     hasOwner = true;
 312                 } else {
 313                     isOwner = false;
 314                     hasOwner = false;
 315                 }
 316
 317                 DOMEntity entity = new DOMEntity(possibleType.get().getValue().toString(),
 318                     (YangInstanceIdentifier) entityNode.getChild(ENTITY_ID_NODE_ID).get().getValue());
 319
 320                 listenerSupport.notifyEntityOwnershipListeners(entity, isOwner, isOwner, hasOwner);
 321             }
 322         });
 323     }
 324
 325     @Override
 326     protected void onStateChanged() {
 327         boolean isLeader = isLeader();
 328         LOG.debug("{}: onStateChanged: isLeader: {}, hasLeader: {}", persistenceId(), isLeader, hasLeader());
 329
 330         // Examine current RAFT state to see if we are in jeopardy, potentially notifying all listeners
 331         final boolean inJeopardy = inJeopardy(getRaftState());
 332         final boolean wasInJeopardy = listenerSupport.setInJeopardy(inJeopardy);
 333         if (inJeopardy != wasInJeopardy) {
 334             LOG.debug("{}: {} jeopardy state, notifying all listeners", persistenceId(),
 335                 inJeopardy ? "entered" : "left");
 336             notifyAllListeners();
 337         }
 338
 339         commitCoordinator.onStateChanged(this, isLeader);
 340
 341         super.onStateChanged();
 342     }
 343
 344     @Override
 345     protected void onLeaderChanged(final String oldLeader, final String newLeader) {
 346         boolean isLeader = isLeader();
 347         LOG.debug("{}: onLeaderChanged: oldLeader: {}, newLeader: {}, isLeader: {}", persistenceId(), oldLeader,
 348                 newLeader, isLeader);
 349
 350         if (isLeader) {
 351
 352             // Re-initialize the downPeerMemberNames from the current akka Cluster state. The previous leader, if any,
 353             // is most likely down however it's possible we haven't received the PeerDown message yet.
 354             initializeDownPeerMemberNamesFromClusterState();
 355
 356             // Clear all existing strategies so that they get re-created when we call createStrategy again
 357             // This allows the strategies to be re-initialized with existing statistics maintained by
 358             // EntityOwnershipStatistics
 359             strategyConfig.clearStrategies();
 360
 361             // Re-assign owners for all members that are known to be down. In a cluster which has greater than
 362             // 3 nodes it is possible for some node beside the leader being down when the leadership transitions
 363             // it makes sense to use this event to re-assign owners for those downed nodes.
 364             Set<String> ownedBy = new HashSet<>(downPeerMemberNames.size() + 1);
 365             for (MemberName downPeerName : downPeerMemberNames) {
 366                 ownedBy.add(downPeerName.getName());
 367             }
 368
 369             // Also try to assign owners for entities that have no current owner. See explanation in onPeerUp.
 370             ownedBy.add("");
 371             selectNewOwnerForEntitiesOwnedBy(ownedBy);
 372         } else {
 373             // The leader changed - notify the coordinator to check if pending modifications need to be sent.
 374             // While onStateChanged also does this, this method handles the case where the shard hears from a
 375             // leader and stays in the follower state. In that case no behavior state change occurs.
 376             commitCoordinator.onStateChanged(this, isLeader);
 377         }
 378
 379         super.onLeaderChanged(oldLeader, newLeader);
 380     }
 381
 382     @Override
 383     protected void onVotingStateChangeComplete() {
 384         // Re-evaluate ownership for all entities - if a member changed from voting to non-voting it should lose
 385         // ownership and vice versa it now is a candidate to become owner.
 386         final List<Modification> modifications = new ArrayList<>();
 387         searchForEntities((entityTypeNode, entityNode) -> {
 388             YangInstanceIdentifier entityPath = YangInstanceIdentifier.builder(ENTITY_TYPES_PATH)
 389                     .node(entityTypeNode.getIdentifier()).node(ENTITY_NODE_ID).node(entityNode.getIdentifier())
 390                     .node(ENTITY_OWNER_NODE_ID).build();
 391
 392             Optional<String> possibleOwner =
 393                     entityNode.getChild(ENTITY_OWNER_NODE_ID).map(node -> node.getValue().toString());
 394             String newOwner = newOwner(possibleOwner.orElse(null), getCandidateNames(entityNode),
 395                     getEntityOwnerElectionStrategy(entityPath));
 396
 397             if (!newOwner.equals(possibleOwner.orElse(""))) {
 398                 modifications.add(new WriteModification(entityPath,
 399                         ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)));
 400             }
 401         });
 402
 403         commitCoordinator.commitModifications(modifications, this);
 404     }
 405
 406     private void initializeDownPeerMemberNamesFromClusterState() {
 407         Optional<Cluster> cluster = getRaftActorContext().getCluster();
 408         if (!cluster.isPresent()) {
 409             return;
 410         }
 411
 412         CurrentClusterState state = cluster.get().state();
 413         Set<Member> unreachable = state.getUnreachable();
 414
 415         LOG.debug(
 416             "{}: initializeDownPeerMemberNamesFromClusterState - current downPeerMemberNames: {}, unreachable: {}",
 417             persistenceId(), downPeerMemberNames, unreachable);
 418
 419         downPeerMemberNames.clear();
 420         for (Member m: unreachable) {
 421             downPeerMemberNames.add(MemberName.forName(m.getRoles().iterator().next()));
 422         }
 423
 424         for (Member m: state.getMembers()) {
 425             if (m.status() != MemberStatus.up() && m.status() != MemberStatus.weaklyUp()) {
 426                 LOG.debug("{}: Adding down member with status {}", persistenceId(), m.status());
 427                 downPeerMemberNames.add(MemberName.forName(m.getRoles().iterator().next()));
 428             }
 429         }
 430
 431         LOG.debug("{}: new downPeerMemberNames: {}", persistenceId(), downPeerMemberNames);
 432     }
 433
 434     private void onCandidateRemoved(final CandidateRemoved message) {
 435         LOG.debug("{}: onCandidateRemoved: {}", persistenceId(), message);
 436
 437         if (isLeader()) {
 438             String currentOwner = getCurrentOwner(message.getEntityPath());
 439             writeNewOwner(message.getEntityPath(),
 440                     newOwner(currentOwner, message.getRemainingCandidates(),
 441                             getEntityOwnerElectionStrategy(message.getEntityPath())));
 442         }
 443     }
 444
 445     private EntityOwnerSelectionStrategy getEntityOwnerElectionStrategy(final YangInstanceIdentifier entityPath) {
 446         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 447         return strategyConfig.createStrategy(entityType, entityOwnershipStatistics.byEntityType(entityType));
 448     }
 449
 450     private void onCandidateAdded(final CandidateAdded message) {
 451         if (!isLeader()) {
 452             return;
 453         }
 454
 455         LOG.debug("{}: onCandidateAdded: {}", persistenceId(), message);
 456
 457         // Since a node's candidate member is only added by the node itself, we can assume the node is up so
 458         // remove it from the downPeerMemberNames.
 459         downPeerMemberNames.remove(MemberName.forName(message.getNewCandidate()));
 460
 461         final String currentOwner = getCurrentOwner(message.getEntityPath());
 462         final EntityOwnerSelectionStrategy strategy = getEntityOwnerElectionStrategy(message.getEntityPath());
 463
 464         // Available members is all the known peers - the number of peers that are down + self
 465         // So if there are 2 peers and 1 is down then availableMembers will be 2
 466         final int availableMembers = getRaftActorContext().getPeerIds().size() - downPeerMemberNames.size() + 1;
 467
 468         LOG.debug("{}: Using strategy {} to select owner, currentOwner = {}", persistenceId(), strategy, currentOwner);
 469
 470         if (strategy.getSelectionDelayInMillis() == 0L) {
 471             writeNewOwner(message.getEntityPath(), newOwner(currentOwner, message.getAllCandidates(),
 472                     strategy));
 473         } else if (message.getAllCandidates().size() == availableMembers) {
 474             LOG.debug("{}: Received the maximum candidates requests : {} writing new owner",
 475                     persistenceId(), availableMembers);
 476             cancelOwnerSelectionTask(message.getEntityPath());
 477             writeNewOwner(message.getEntityPath(), newOwner(currentOwner, message.getAllCandidates(),
 478                     strategy));
 479         } else {
 480             scheduleOwnerSelection(message.getEntityPath(), message.getAllCandidates(), strategy);
 481         }
 482     }
 483
 484     private void onPeerDown(final PeerDown peerDown) {
 485         LOG.info("{}: onPeerDown: {}", persistenceId(), peerDown);
 486
 487         MemberName downMemberName = peerDown.getMemberName();
 488         if (downPeerMemberNames.add(downMemberName) && isLeader()) {
 489             // Select new owners for entities owned by the down peer and which have other candidates. For an entity for
 490             // which the down peer is the only candidate, we leave it as the owner and don't clear it. This is done to
 491             // handle the case where the peer member process is actually still running but the node is partitioned.
 492             // When the partition is healed, the peer just remains as the owner. If the peer process actually restarted,
 493             // it will first remove all its candidates on startup. If another candidate is registered during the time
 494             // the peer is down, the new candidate will be selected as the new owner.
 495
 496             selectNewOwnerForEntitiesOwnedBy(ImmutableSet.of(downMemberName.getName()));
 497         }
 498     }
 499
 500     private void selectNewOwnerForEntitiesOwnedBy(final Set<String> ownedBy) {
 501         final List<Modification> modifications = new ArrayList<>();
 502         searchForEntitiesOwnedBy(ownedBy, (entityTypeNode, entityNode) -> {
 503             YangInstanceIdentifier entityPath = YangInstanceIdentifier.builder(ENTITY_TYPES_PATH)
 504                     .node(entityTypeNode.getIdentifier()).node(ENTITY_NODE_ID).node(entityNode.getIdentifier())
 505                     .node(ENTITY_OWNER_NODE_ID).build();
 506             String newOwner = newOwner(getCurrentOwner(entityPath), getCandidateNames(entityNode),
 507                     getEntityOwnerElectionStrategy(entityPath));
 508
 509             if (!newOwner.isEmpty()) {
 510                 LOG.debug("{}: Found entity {}, writing new owner {}", persistenceId(), entityPath, newOwner);
 511
 512                 modifications.add(new WriteModification(entityPath,
 513                     ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)));
 514
 515             } else {
 516                 LOG.debug("{}: Found entity {} but no other candidates - not clearing owner", persistenceId(),
 517                         entityPath);
 518             }
 519         });
 520
 521         commitCoordinator.commitModifications(modifications, this);
 522     }
 523
 524     private void onPeerUp(final PeerUp peerUp) {
 525         LOG.debug("{}: onPeerUp: {}", persistenceId(), peerUp);
 526
 527         downPeerMemberNames.remove(peerUp.getMemberName());
 528
 529         // Notify the coordinator to check if pending modifications need to be sent. We do this here
 530         // to handle the case where the leader's peer address isn't known yet when a prior state or
 531         // leader change occurred.
 532         commitCoordinator.onStateChanged(this, isLeader());
 533
 534         if (isLeader()) {
 535             // Try to assign owners for entities that have no current owner. It's possible the peer that is now up
 536             // had previously registered as a candidate and was the only candidate but the owner write tx couldn't be
 537             // committed due to a leader change. Eg, the leader is able to successfully commit the candidate add tx but
 538             // becomes isolated before it can commit the owner change and switches to follower. The majority partition
 539             // with a new leader has the candidate but the entity has no owner. When the partition is healed and the
 540             // previously isolated leader reconnects, we'll receive onPeerUp and, if there's still no owner, the
 541             // previous leader will gain ownership.
 542             selectNewOwnerForEntitiesOwnedBy(ImmutableSet.of(""));
 543         }
 544     }
 545
 546     private static Collection<String> getCandidateNames(final MapEntryNode entity) {
 547         return entity.getChild(CANDIDATE_NODE_ID).map(child -> {
 548             Collection<MapEntryNode> candidates = ((MapNode) child).getValue();
 549             Collection<String> candidateNames = new ArrayList<>(candidates.size());
 550             for (MapEntryNode candidate: candidates) {
 551                 candidateNames.add(candidate.getChild(CANDIDATE_NAME_NODE_ID).get().getValue().toString());
 552             }
 553             return candidateNames;
 554         }).orElse(ImmutableList.of());
 555     }
 556
 557     private void searchForEntitiesOwnedBy(final Set<String> ownedBy, final EntityWalker walker) {
 558         LOG.debug("{}: Searching for entities owned by {}", persistenceId(), ownedBy);
 559
 560         searchForEntities((entityTypeNode, entityNode) -> {
 561             Optional<DataContainerChild<? extends PathArgument, ?>> possibleOwner =
 562                     entityNode.getChild(ENTITY_OWNER_NODE_ID);
 563             String currentOwner = possibleOwner.isPresent() ? possibleOwner.get().getValue().toString() : "";
 564             if (ownedBy.contains(currentOwner)) {
 565                 walker.onEntity(entityTypeNode, entityNode);
 566             }
 567         });
 568     }
 569
 570     private void removeCandidateFromEntities(final MemberName member) {
 571         final List<Modification> modifications = new ArrayList<>();
 572         searchForEntities((entityTypeNode, entityNode) -> {
 573             if (hasCandidate(entityNode, member)) {
 574                 YangInstanceIdentifier entityId =
 575                         (YangInstanceIdentifier) entityNode.getIdentifier().getKeyValues().get(ENTITY_ID_QNAME);
 576                 YangInstanceIdentifier candidatePath = candidatePath(
 577                         entityTypeNode.getIdentifier().getKeyValues().get(ENTITY_TYPE_QNAME).toString(),
 578                         entityId, member.getName());
 579
 580                 LOG.info("{}: Found entity {}, removing candidate {}, path {}", persistenceId(), entityId,
 581                         member, candidatePath);
 582
 583                 modifications.add(new DeleteModification(candidatePath));
 584             }
 585         });
 586
 587         commitCoordinator.commitModifications(modifications, this);
 588     }
 589
 590     private static boolean hasCandidate(final MapEntryNode entity, final MemberName candidateName) {
 591         return entity.getChild(CANDIDATE_NODE_ID)
 592                 .flatMap(child -> ((MapNode)child).getChild(candidateNodeKey(candidateName.getName())))
 593                 .isPresent();
 594     }
 595
 596     private void searchForEntities(final EntityWalker walker) {
 597         Optional<NormalizedNode<?, ?>> possibleEntityTypes = getDataStore().readNode(ENTITY_TYPES_PATH);
 598         if (!possibleEntityTypes.isPresent()) {
 599             return;
 600         }
 601
 602         for (MapEntryNode entityType : ((MapNode) possibleEntityTypes.get()).getValue()) {
 603             Optional<DataContainerChild<?, ?>> possibleEntities = entityType.getChild(ENTITY_NODE_ID);
 604             if (!possibleEntities.isPresent()) {
 605                 // shouldn't happen but handle anyway
 606                 continue;
 607             }
 608
 609             for (MapEntryNode entity:  ((MapNode) possibleEntities.get()).getValue()) {
 610                 walker.onEntity(entityType, entity);
 611             }
 612         }
 613     }
 614
 615     private void writeNewOwner(final YangInstanceIdentifier entityPath, final String newOwner) {
 616         LOG.debug("{}: Writing new owner {} for entity {}", persistenceId(), newOwner, entityPath);
 617
 618         commitCoordinator.commitModification(new WriteModification(entityPath.node(ENTITY_OWNER_QNAME),
 619                 ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)), this);
 620     }
 621
 622     /**
 623      * Schedule a new owner selection job. Cancelling any outstanding job if it has not been cancelled.
 624      */
 625     private void scheduleOwnerSelection(final YangInstanceIdentifier entityPath, final Collection<String> allCandidates,
 626                                        final EntityOwnerSelectionStrategy strategy) {
 627         cancelOwnerSelectionTask(entityPath);
 628
 629         LOG.debug("{}: Scheduling owner selection after {} ms", persistenceId(), strategy.getSelectionDelayInMillis());
 630
 631         final Cancellable lastScheduledTask = context().system().scheduler().scheduleOnce(
 632                 FiniteDuration.apply(strategy.getSelectionDelayInMillis(), TimeUnit.MILLISECONDS), self(),
 633                 new SelectOwner(entityPath, allCandidates, strategy), context().system().dispatcher(), self());
 634
 635         entityToScheduledOwnershipTask.put(entityPath, lastScheduledTask);
 636     }
 637
 638     private void cancelOwnerSelectionTask(final YangInstanceIdentifier entityPath) {
 639         final Cancellable lastScheduledTask = entityToScheduledOwnershipTask.get(entityPath);
 640         if (lastScheduledTask != null && !lastScheduledTask.isCancelled()) {
 641             lastScheduledTask.cancel();
 642         }
 643     }
 644
 645     private String newOwner(final String currentOwner, final Collection<String> candidates,
 646             final EntityOwnerSelectionStrategy ownerSelectionStrategy) {
 647         Collection<String> viableCandidates = getViableCandidates(candidates);
 648         if (viableCandidates.isEmpty()) {
 649             return "";
 650         }
 651         return ownerSelectionStrategy.newOwner(currentOwner, viableCandidates);
 652     }
 653
 654     private Collection<String> getViableCandidates(final Collection<String> candidates) {
 655         Map<MemberName, VotingState> memberToVotingState = new HashMap<>();
 656         getRaftActorContext().getPeers().forEach(peerInfo -> memberToVotingState.put(
 657                 ShardIdentifier.fromShardIdString(peerInfo.getId()).getMemberName(), peerInfo.getVotingState()));
 658
 659         Collection<String> viableCandidates = new ArrayList<>();
 660
 661         for (String candidate : candidates) {
 662             MemberName memberName = MemberName.forName(candidate);
 663             if (memberToVotingState.get(memberName) != VotingState.NON_VOTING
 664                     && !downPeerMemberNames.contains(memberName)) {
 665                 viableCandidates.add(candidate);
 666             }
 667         }
 668         return viableCandidates;
 669     }
 670
 671     private String getCurrentOwner(final YangInstanceIdentifier entityId) {
 672         return getDataStore().readNode(entityId.node(ENTITY_OWNER_QNAME))
 673                 .map(owner -> owner.getValue().toString())
 674                 .orElse(null);
 675     }
 676
 677     @FunctionalInterface
 678     private interface EntityWalker {
 679         void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode);
 680     }
 681
 682     public static Builder newBuilder() {
 683         return new Builder();
 684     }
 685
 686     static class Builder extends Shard.AbstractBuilder<Builder, EntityOwnershipShard> {
 687         private MemberName localMemberName;
 688         private EntityOwnerSelectionStrategyConfig ownerSelectionStrategyConfig;
 689
 690         protected Builder() {
 691             super(EntityOwnershipShard.class);
 692         }
 693
 694         Builder localMemberName(final MemberName newLocalMemberName) {
 695             checkSealed();
 696             this.localMemberName = newLocalMemberName;
 697             return this;
 698         }
 699
 700         Builder ownerSelectionStrategyConfig(final EntityOwnerSelectionStrategyConfig newOwnerSelectionStrategyConfig) {
 701             checkSealed();
 702             this.ownerSelectionStrategyConfig = newOwnerSelectionStrategyConfig;
 703             return this;
 704         }
 705
 706         @Override
 707         protected void verify() {
 708             super.verify();
 709             Preconditions.checkNotNull(localMemberName, "localMemberName should not be null");
 710             Preconditions.checkNotNull(ownerSelectionStrategyConfig, "ownerSelectionStrategyConfig should not be null");
 711         }
 712     }
 713 }