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.candidateMapEntry;
  22 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.candidateNodeKey;
  23 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.candidatePath;
  24 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.createEntity;
  25 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.entityOwnersWithCandidate;
  26 import akka.actor.ActorRef;
  27 import akka.actor.ActorSelection;
  28 import akka.actor.Props;
  29 import akka.pattern.Patterns;
  30 import com.google.common.annotations.VisibleForTesting;
  31 import com.google.common.base.Optional;
  32 import com.google.common.base.Strings;
  33 import java.util.ArrayList;
  34 import java.util.Collection;
  35 import java.util.HashMap;
  36 import java.util.HashSet;
  37 import java.util.Map;
  38 import java.util.Set;
  39 import java.util.concurrent.TimeUnit;
  40 import org.opendaylight.controller.cluster.datastore.DatastoreContext;
  41 import org.opendaylight.controller.cluster.datastore.Shard;
  42 import org.opendaylight.controller.cluster.datastore.entityownership.messages.CandidateAdded;
  43 import org.opendaylight.controller.cluster.datastore.entityownership.messages.CandidateRemoved;
  44 import org.opendaylight.controller.cluster.datastore.entityownership.messages.RegisterCandidateLocal;
  45 import org.opendaylight.controller.cluster.datastore.entityownership.messages.RegisterListenerLocal;
  46 import org.opendaylight.controller.cluster.datastore.entityownership.messages.SelectOwner;
  47 import org.opendaylight.controller.cluster.datastore.entityownership.messages.UnregisterCandidateLocal;
  48 import org.opendaylight.controller.cluster.datastore.entityownership.messages.UnregisterListenerLocal;
  49 import org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy.EntityOwnerSelectionStrategy;
  50 import org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy.EntityOwnerSelectionStrategyWrapper;
  51 import org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy.FirstCandidateSelectionStrategy;
  52 import org.opendaylight.controller.cluster.datastore.identifiers.ShardIdentifier;
  53 import org.opendaylight.controller.cluster.datastore.messages.BatchedModifications;
  54 import org.opendaylight.controller.cluster.datastore.messages.PeerDown;
  55 import org.opendaylight.controller.cluster.datastore.messages.PeerUp;
  56 import org.opendaylight.controller.cluster.datastore.messages.SuccessReply;
  57 import org.opendaylight.controller.cluster.datastore.modification.DeleteModification;
  58 import org.opendaylight.controller.cluster.datastore.modification.MergeModification;
  59 import org.opendaylight.controller.cluster.datastore.modification.WriteModification;
  60 import org.opendaylight.controller.md.sal.common.api.clustering.Entity;
  61 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
  62 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
  63 import org.opendaylight.yangtools.yang.data.api.schema.DataContainerChild;
  64 import org.opendaylight.yangtools.yang.data.api.schema.MapEntryNode;
  65 import org.opendaylight.yangtools.yang.data.api.schema.MapNode;
  66 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
  67 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeSnapshot;
  68 import org.opendaylight.yangtools.yang.data.impl.schema.ImmutableNodes;
  69 import org.opendaylight.yangtools.yang.model.api.SchemaContext;
  70 import scala.concurrent.Future;
  71
  72 /**
  73  * Special Shard for EntityOwnership.
  74  *
  75  * @author Thomas Pantelis
  76  */
  77 class EntityOwnershipShard extends Shard {
  78     private final String localMemberName;
  79     private final EntityOwnershipShardCommitCoordinator commitCoordinator;
  80     private final EntityOwnershipListenerSupport listenerSupport;
  81     private final Set<String> downPeerMemberNames = new HashSet<>();
  82     private final Map<String, String> peerIdToMemberNames = new HashMap<>();
  83     private final Map<String, EntityOwnerSelectionStrategyWrapper> ownerSelectionStrategies = new HashMap<>();
  84     private final EntityOwnerSelectionStrategyWrapper defaultEntityOwnerSelectionStrategy;
  85
  86     private static DatastoreContext noPersistenceDatastoreContext(DatastoreContext datastoreContext) {
  87         return DatastoreContext.newBuilderFrom(datastoreContext).persistent(false).build();
  88     }
  89
  90     protected EntityOwnershipShard(ShardIdentifier name, Map<String, String> peerAddresses,
  91             DatastoreContext datastoreContext, SchemaContext schemaContext, String localMemberName) {
  92         super(name, peerAddresses, noPersistenceDatastoreContext(datastoreContext), schemaContext);
  93         this.localMemberName = localMemberName;
  94         this.commitCoordinator = new EntityOwnershipShardCommitCoordinator(localMemberName, LOG);
  95         this.listenerSupport = new EntityOwnershipListenerSupport(getContext(), persistenceId());
  96         this.defaultEntityOwnerSelectionStrategy =
  97                 createEntityOwnerSelectionStrategyWrapper(FirstCandidateSelectionStrategy.INSTANCE);
  98
  99         for(String peerId: peerAddresses.keySet()) {
 100             ShardIdentifier shardId = ShardIdentifier.builder().fromShardIdString(peerId).build();
 101             peerIdToMemberNames.put(peerId, shardId.getMemberName());
 102         }
 103     }
 104
 105     @Override
 106     protected void onDatastoreContext(DatastoreContext context) {
 107         super.onDatastoreContext(noPersistenceDatastoreContext(context));
 108     }
 109
 110     @Override
 111     protected void onRecoveryComplete() {
 112         super.onRecoveryComplete();
 113
 114         new CandidateListChangeListener(getSelf(), persistenceId()).init(getDataStore());
 115         new EntityOwnerChangeListener(localMemberName, listenerSupport).init(getDataStore());
 116     }
 117
 118     @Override
 119     public void onReceiveCommand(final Object message) throws Exception {
 120         if(message instanceof RegisterCandidateLocal) {
 121             onRegisterCandidateLocal((RegisterCandidateLocal) message);
 122         } else if(message instanceof UnregisterCandidateLocal) {
 123             onUnregisterCandidateLocal((UnregisterCandidateLocal)message);
 124         } else if(message instanceof CandidateAdded){
 125             onCandidateAdded((CandidateAdded) message);
 126         } else if(message instanceof CandidateRemoved){
 127             onCandidateRemoved((CandidateRemoved) message);
 128         } else if(message instanceof PeerDown) {
 129             onPeerDown((PeerDown) message);
 130         } else if(message instanceof PeerUp) {
 131             onPeerUp((PeerUp) message);
 132         } else if(message instanceof RegisterListenerLocal) {
 133             onRegisterListenerLocal((RegisterListenerLocal)message);
 134         } else if(message instanceof UnregisterListenerLocal) {
 135             onUnregisterListenerLocal((UnregisterListenerLocal) message);
 136         } else if(message instanceof SelectOwner) {
 137             onSelectOwner((SelectOwner) message);
 138         } else if(!commitCoordinator.handleMessage(message, this)) {
 139             super.onReceiveCommand(message);
 140         }
 141     }
 142
 143     private void onSelectOwner(SelectOwner selectOwner) {
 144         String currentOwner = getCurrentOwner(selectOwner.getEntityPath());
 145         if(Strings.isNullOrEmpty(currentOwner)) {
 146             writeNewOwner(selectOwner.getEntityPath(), newOwner(selectOwner.getAllCandidates(),
 147                     selectOwner.getOwnerSelectionStrategy()));
 148         }
 149     }
 150
 151     private void onRegisterCandidateLocal(RegisterCandidateLocal registerCandidate) {
 152         LOG.debug("{}: onRegisterCandidateLocal: {}", persistenceId(), registerCandidate);
 153
 154         listenerSupport.setHasCandidateForEntity(registerCandidate.getEntity());
 155
 156         NormalizedNode<?, ?> entityOwners = entityOwnersWithCandidate(registerCandidate.getEntity().getType(),
 157                 registerCandidate.getEntity().getId(), localMemberName);
 158         commitCoordinator.commitModification(new MergeModification(ENTITY_OWNERS_PATH, entityOwners), this);
 159
 160         getSender().tell(SuccessReply.INSTANCE, getSelf());
 161     }
 162
 163     private void onUnregisterCandidateLocal(UnregisterCandidateLocal unregisterCandidate) {
 164         LOG.debug("{}: onUnregisterCandidateLocal: {}", persistenceId(), unregisterCandidate);
 165
 166         Entity entity = unregisterCandidate.getEntity();
 167         listenerSupport.unsetHasCandidateForEntity(entity);
 168
 169         YangInstanceIdentifier candidatePath = candidatePath(entity.getType(), entity.getId(), localMemberName);
 170         commitCoordinator.commitModification(new DeleteModification(candidatePath), this);
 171
 172         getSender().tell(SuccessReply.INSTANCE, getSelf());
 173     }
 174
 175     private void onRegisterListenerLocal(final RegisterListenerLocal registerListener) {
 176         LOG.debug("{}: onRegisterListenerLocal: {}", persistenceId(), registerListener);
 177
 178         listenerSupport.addEntityOwnershipListener(registerListener.getEntityType(), registerListener.getListener());
 179
 180         getSender().tell(SuccessReply.INSTANCE, getSelf());
 181
 182         searchForEntitiesOwnedBy(localMemberName, new EntityWalker() {
 183             @Override
 184             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 185                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleType =
 186                         entityTypeNode.getChild(ENTITY_TYPE_NODE_ID);
 187                 String entityType = possibleType.isPresent() ? possibleType.get().getValue().toString() : null;
 188                 if (registerListener.getEntityType().equals(entityType)) {
 189                     Entity entity = new Entity(entityType,
 190                             (YangInstanceIdentifier) entityNode.getChild(ENTITY_ID_NODE_ID).get().getValue());
 191                     listenerSupport.notifyEntityOwnershipListener(entity, false, true, true, registerListener.getListener());
 192                 }
 193             }
 194         });
 195     }
 196
 197     private void onUnregisterListenerLocal(UnregisterListenerLocal unregisterListener) {
 198         LOG.debug("{}: onUnregisterListenerLocal: {}", persistenceId(), unregisterListener);
 199
 200         listenerSupport.removeEntityOwnershipListener(unregisterListener.getEntityType(), unregisterListener.getListener());
 201
 202         getSender().tell(SuccessReply.INSTANCE, getSelf());
 203     }
 204
 205     void tryCommitModifications(final BatchedModifications modifications) {
 206         if(isLeader()) {
 207             LOG.debug("{}: Committing BatchedModifications {} locally", persistenceId(), modifications.getTransactionID());
 208
 209             // Note that it's possible the commit won't get consensus and will timeout and not be applied
 210             // to the state. However we don't need to retry it in that case b/c it will be committed to
 211             // the journal first and, once a majority of followers come back on line and it is replicated,
 212             // it will be applied at that point.
 213             handleBatchedModificationsLocal(modifications, self());
 214         } else {
 215             final ActorSelection leader = getLeader();
 216             if (leader != null) {
 217                 if(LOG.isDebugEnabled()) {
 218                     LOG.debug("{}: Sending BatchedModifications {} to leader {}", persistenceId(),
 219                             modifications.getTransactionID(), leader);
 220                 }
 221
 222                 Future<Object> future = Patterns.ask(leader, modifications, TimeUnit.SECONDS.toMillis(
 223                         getDatastoreContext().getShardTransactionCommitTimeoutInSeconds()));
 224
 225                 Patterns.pipe(future, getContext().dispatcher()).pipeTo(getSelf(), ActorRef.noSender());
 226             }
 227         }
 228     }
 229
 230     boolean hasLeader() {
 231         return getLeader() != null && !isIsolatedLeader();
 232     }
 233
 234     @Override
 235     protected void onStateChanged() {
 236         super.onStateChanged();
 237
 238         commitCoordinator.onStateChanged(this, isLeader());
 239     }
 240
 241     @Override
 242     protected void onLeaderChanged(String oldLeader, String newLeader) {
 243         super.onLeaderChanged(oldLeader, newLeader);
 244
 245         LOG.debug("{}: onLeaderChanged: oldLeader: {}, newLeader: {}, isLeader: {}", persistenceId(), oldLeader,
 246                 newLeader, isLeader());
 247
 248         if(isLeader()) {
 249             // We were just elected leader. If the old leader is down, select new owners for the entities
 250             // owned by the down leader.
 251
 252             String oldLeaderMemberName = peerIdToMemberNames.get(oldLeader);
 253
 254             LOG.debug("{}: oldLeaderMemberName: {}", persistenceId(), oldLeaderMemberName);
 255
 256             if(downPeerMemberNames.contains(oldLeaderMemberName)) {
 257                 selectNewOwnerForEntitiesOwnedBy(oldLeaderMemberName);
 258             }
 259         }
 260     }
 261
 262     private void onCandidateRemoved(CandidateRemoved message) {
 263         LOG.debug("{}: onCandidateRemoved: {}", persistenceId(), message);
 264
 265         if(isLeader()) {
 266             String currentOwner = getCurrentOwner(message.getEntityPath());
 267             if(message.getRemovedCandidate().equals(currentOwner)){
 268                 writeNewOwner(message.getEntityPath(),
 269                         newOwner(message.getRemainingCandidates(), getEntityOwnerElectionStrategyWrapper(message.getEntityPath())));
 270             }
 271         } else {
 272             // We're not the leader. If the removed candidate is our local member then check if we actually
 273             // have a local candidate registered. If we do then we must have been partitioned from the leader
 274             // and the leader removed our candidate since the leader can't tell the difference between a
 275             // temporary network partition and a node's process actually restarted. So, in that case, re-add
 276             // our candidate.
 277             if(localMemberName.equals(message.getRemovedCandidate()) &&
 278                     listenerSupport.hasCandidateForEntity(createEntity(message.getEntityPath()))) {
 279                 LOG.debug("Local candidate member was removed but a local candidate is registered for {}" +
 280                     " - adding back local candidate", message.getEntityPath());
 281
 282                 commitCoordinator.commitModification(new MergeModification(
 283                         candidatePath(message.getEntityPath(), localMemberName),
 284                         candidateMapEntry(localMemberName)), this);
 285             }
 286         }
 287     }
 288
 289     private EntityOwnerSelectionStrategyWrapper getEntityOwnerElectionStrategyWrapper(YangInstanceIdentifier entityPath) {
 290         String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 291         EntityOwnerSelectionStrategyWrapper entityOwnerSelectionStrategy = ownerSelectionStrategies.get(entityType);
 292
 293         if(entityOwnerSelectionStrategy == null){
 294             entityOwnerSelectionStrategy = defaultEntityOwnerSelectionStrategy;
 295             ownerSelectionStrategies.put(entityType, entityOwnerSelectionStrategy);
 296         }
 297
 298         return entityOwnerSelectionStrategy;
 299     }
 300
 301     private void onCandidateAdded(CandidateAdded message) {
 302         if(!isLeader()){
 303             return;
 304         }
 305
 306         LOG.debug("{}: onCandidateAdded: {}", persistenceId(), message);
 307
 308         // Since a node's candidate member is only added by the node itself, we can assume the node is up so
 309         // remove it from the downPeerMemberNames.
 310         downPeerMemberNames.remove(message.getNewCandidate());
 311
 312         String currentOwner = getCurrentOwner(message.getEntityPath());
 313         if(Strings.isNullOrEmpty(currentOwner)){
 314             EntityOwnerSelectionStrategyWrapper strategy = getEntityOwnerElectionStrategyWrapper(message.getEntityPath());
 315             if(strategy.selectionDelayInMillis() == 0L) {
 316                 writeNewOwner(message.getEntityPath(), newOwner(message.getAllCandidates(), strategy));
 317             } else {
 318                 strategy.scheduleOwnerSelection(message.getEntityPath(), message.getAllCandidates());
 319             }
 320         }
 321     }
 322
 323     private void onPeerDown(PeerDown peerDown) {
 324         LOG.info("{}: onPeerDown: {}", persistenceId(), peerDown);
 325
 326         String downMemberName = peerDown.getMemberName();
 327         if(downPeerMemberNames.add(downMemberName) && isLeader()) {
 328             // Remove the down peer as a candidate from all entities.
 329             removeCandidateFromEntities(downMemberName);
 330         }
 331     }
 332
 333     private void onPeerUp(PeerUp peerUp) {
 334         LOG.debug("{}: onPeerUp: {}", persistenceId(), peerUp);
 335
 336         peerIdToMemberNames.put(peerUp.getPeerId(), peerUp.getMemberName());
 337         downPeerMemberNames.remove(peerUp.getMemberName());
 338     }
 339
 340     private void selectNewOwnerForEntitiesOwnedBy(String owner) {
 341         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 342         searchForEntitiesOwnedBy(owner, new EntityWalker() {
 343             @Override
 344             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 345
 346                 YangInstanceIdentifier entityPath = YangInstanceIdentifier.builder(ENTITY_TYPES_PATH).
 347                         node(entityTypeNode.getIdentifier()).node(ENTITY_NODE_ID).node(entityNode.getIdentifier()).
 348                         node(ENTITY_OWNER_NODE_ID).build();
 349
 350                 Object newOwner = newOwner(getCandidateNames(entityNode), getEntityOwnerElectionStrategyWrapper(entityPath));
 351
 352                 LOG.debug("{}: Found entity {}, writing new owner {}", persistenceId(), entityPath, newOwner);
 353
 354                 modifications.addModification(new WriteModification(entityPath,
 355                         ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)));
 356             }
 357         });
 358
 359         commitCoordinator.commitModifications(modifications, this);
 360     }
 361
 362     private void removeCandidateFromEntities(final String owner) {
 363         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 364         searchForEntities(new EntityWalker() {
 365             @Override
 366             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 367                 if (hasCandidate(entityNode, owner)) {
 368                     YangInstanceIdentifier entityId =
 369                             (YangInstanceIdentifier) entityNode.getIdentifier().getKeyValues().get(ENTITY_ID_QNAME);
 370                     YangInstanceIdentifier candidatePath = candidatePath(
 371                             entityTypeNode.getIdentifier().getKeyValues().get(ENTITY_TYPE_QNAME).toString(),
 372                             entityId, owner);
 373
 374                     LOG.info("{}: Found entity {}, removing candidate {}, path {}", persistenceId(), entityId,
 375                             owner, candidatePath);
 376
 377                     modifications.addModification(new DeleteModification(candidatePath));
 378                 }
 379             }
 380         });
 381
 382         commitCoordinator.commitModifications(modifications, this);
 383     }
 384
 385     private boolean hasCandidate(MapEntryNode entity, String candidateName) {
 386         return ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getChild(candidateNodeKey(candidateName)).isPresent();
 387     }
 388
 389     private void searchForEntitiesOwnedBy(final String owner, final EntityWalker walker) {
 390         DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
 391         Optional<NormalizedNode<?, ?>> possibleEntityTypes = snapshot.readNode(ENTITY_TYPES_PATH);
 392         if(!possibleEntityTypes.isPresent()) {
 393             return;
 394         }
 395
 396         LOG.debug("{}: Searching for entities owned by {}", persistenceId(), owner);
 397
 398         searchForEntities(new EntityWalker() {
 399             @Override
 400             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 401                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleOwner =
 402                         entityNode.getChild(ENTITY_OWNER_NODE_ID);
 403                 if(possibleOwner.isPresent() && owner.equals(possibleOwner.get().getValue().toString())) {
 404                     walker.onEntity(entityTypeNode, entityNode);
 405                 }
 406             }
 407         });
 408     }
 409
 410     private void searchForEntities(EntityWalker walker) {
 411         DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
 412         Optional<NormalizedNode<?, ?>> possibleEntityTypes = snapshot.readNode(ENTITY_TYPES_PATH);
 413         if(!possibleEntityTypes.isPresent()) {
 414             return;
 415         }
 416
 417         for(MapEntryNode entityType:  ((MapNode) possibleEntityTypes.get()).getValue()) {
 418             Optional<DataContainerChild<? extends PathArgument, ?>> possibleEntities =
 419                     entityType.getChild(ENTITY_NODE_ID);
 420             if(!possibleEntities.isPresent()) {
 421                 continue; // shouldn't happen but handle anyway
 422             }
 423
 424             for(MapEntryNode entity:  ((MapNode) possibleEntities.get()).getValue()) {
 425                 walker.onEntity(entityType, entity);
 426             }
 427         }
 428     }
 429
 430     private Collection<String> getCandidateNames(MapEntryNode entity) {
 431         Collection<MapEntryNode> candidates = ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getValue();
 432         Collection<String> candidateNames = new ArrayList<>(candidates.size());
 433         for(MapEntryNode candidate: candidates) {
 434             candidateNames.add(candidate.getChild(CANDIDATE_NAME_NODE_ID).get().getValue().toString());
 435         }
 436
 437         return candidateNames;
 438     }
 439
 440     private void writeNewOwner(YangInstanceIdentifier entityPath, String newOwner) {
 441         LOG.debug("{}: Writing new owner {} for entity {}", persistenceId(), newOwner, entityPath);
 442
 443         commitCoordinator.commitModification(new WriteModification(entityPath.node(ENTITY_OWNER_QNAME),
 444                 ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)), this);
 445     }
 446
 447     private String newOwner(Collection<String> candidates, EntityOwnerSelectionStrategy ownerSelectionStrategy) {
 448         Collection<String> viableCandidates = getViableCandidates(candidates);
 449         if(viableCandidates.size() == 0){
 450             return "";
 451         }
 452         return ownerSelectionStrategy.newOwner(viableCandidates);
 453     }
 454
 455     private Collection<String> getViableCandidates(Collection<String> candidates) {
 456         Collection<String> viableCandidates = new ArrayList<>();
 457
 458         for (String candidate : candidates) {
 459             if (!downPeerMemberNames.contains(candidate)) {
 460                 viableCandidates.add(candidate);
 461             }
 462         }
 463         return viableCandidates;
 464     }
 465
 466     private String getCurrentOwner(YangInstanceIdentifier entityId) {
 467         DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
 468         Optional<NormalizedNode<?, ?>> optionalEntityOwner = snapshot.readNode(entityId.node(ENTITY_OWNER_QNAME));
 469         if(optionalEntityOwner.isPresent()){
 470             return optionalEntityOwner.get().getValue().toString();
 471         }
 472         return null;
 473     }
 474
 475     private EntityOwnerSelectionStrategyWrapper createEntityOwnerSelectionStrategyWrapper(EntityOwnerSelectionStrategy entityOwnerSelectionStrategy){
 476         return new EntityOwnerSelectionStrategyWrapper(context().system().scheduler(), self(),
 477                 context().system().dispatcher(), entityOwnerSelectionStrategy);
 478     }
 479
 480     @VisibleForTesting
 481     void addEntityOwnerSelectionStrategy(String entityType, Class<? extends EntityOwnerSelectionStrategy> ownerSelectionStrategyClass){
 482         try {
 483             EntityOwnerSelectionStrategyWrapper strategy =
 484                     createEntityOwnerSelectionStrategyWrapper(ownerSelectionStrategyClass.newInstance());
 485             ownerSelectionStrategies.put(entityType, strategy);
 486         } catch (InstantiationException | IllegalAccessException e) {
 487             LOG.error("Exception occurred when adding election strategy", e);
 488         }
 489     }
 490
 491     public static Props props(final ShardIdentifier name, final Map<String, String> peerAddresses,
 492             final DatastoreContext datastoreContext, final SchemaContext schemaContext, final String localMemberName) {
 493         return Props.create(new Creator(name, peerAddresses, datastoreContext, schemaContext, localMemberName));
 494     }
 495
 496     private static class Creator extends AbstractShardCreator {
 497         private static final long serialVersionUID = 1L;
 498
 499         private final String localMemberName;
 500
 501         Creator(final ShardIdentifier name, final Map<String, String> peerAddresses,
 502                 final DatastoreContext datastoreContext, final SchemaContext schemaContext,
 503                 final String localMemberName) {
 504             super(name, peerAddresses, datastoreContext, schemaContext);
 505             this.localMemberName = localMemberName;
 506         }
 507
 508         @Override
 509         public Shard create() throws Exception {
 510             return new EntityOwnershipShard(name, peerAddresses, datastoreContext, schemaContext, localMemberName);
 511         }
 512     }
 513
 514     private static interface EntityWalker {
 515         void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode);
 516     }
 517
 518 }