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