TransportReplicationAction.java

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 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch licenses this file to you under
 * the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.elasticsearch.action.support.replication;

import org.apache.logging.log4j.message.ParameterizedMessage;
import org.apache.lucene.store.AlreadyClosedException;
import org.elasticsearch.Assertions;
import org.elasticsearch.ElasticsearchException;
import org.elasticsearch.ExceptionsHelper;
import org.elasticsearch.action.ActionListener;
import org.elasticsearch.action.ActionListenerResponseHandler;
import org.elasticsearch.action.ActionResponse;
import org.elasticsearch.action.UnavailableShardsException;
import org.elasticsearch.action.support.ActionFilters;
import org.elasticsearch.action.support.ActiveShardCount;
import org.elasticsearch.action.support.ChannelActionListener;
import org.elasticsearch.action.support.TransportAction;
import org.elasticsearch.action.support.TransportActions;
import org.elasticsearch.client.transport.NoNodeAvailableException;
import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.ClusterStateObserver;
import org.elasticsearch.cluster.action.shard.ShardStateAction;
import org.elasticsearch.cluster.block.ClusterBlockException;
import org.elasticsearch.cluster.block.ClusterBlockLevel;
import org.elasticsearch.cluster.metadata.IndexMetaData;
import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
import org.elasticsearch.cluster.node.DiscoveryNode;
import org.elasticsearch.cluster.routing.AllocationId;
import org.elasticsearch.cluster.routing.IndexShardRoutingTable;
import org.elasticsearch.cluster.routing.ShardRouting;
import org.elasticsearch.cluster.service.ClusterService;
import org.elasticsearch.common.Nullable;
import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.common.io.stream.StreamOutput;
import org.elasticsearch.common.io.stream.Writeable;
import org.elasticsearch.common.lease.Releasable;
import org.elasticsearch.common.lease.Releasables;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.unit.TimeValue;
import org.elasticsearch.common.util.concurrent.AbstractRunnable;
import org.elasticsearch.index.IndexNotFoundException;
import org.elasticsearch.index.IndexService;
import org.elasticsearch.index.seqno.SequenceNumbers;
import org.elasticsearch.index.shard.IndexShard;
import org.elasticsearch.index.shard.IndexShardClosedException;
import org.elasticsearch.index.shard.ReplicationGroup;
import org.elasticsearch.index.shard.ShardId;
import org.elasticsearch.index.shard.ShardNotFoundException;
import org.elasticsearch.index.shard.ShardNotInPrimaryModeException;
import org.elasticsearch.indices.IndexClosedException;
import org.elasticsearch.indices.IndicesService;
import org.elasticsearch.node.NodeClosedException;
import org.elasticsearch.tasks.Task;
import org.elasticsearch.tasks.TaskId;
import org.elasticsearch.threadpool.ThreadPool;
import org.elasticsearch.transport.ConnectTransportException;
import org.elasticsearch.transport.TransportChannel;
import org.elasticsearch.transport.TransportException;
import org.elasticsearch.transport.TransportRequest;
import org.elasticsearch.transport.TransportRequestOptions;
import org.elasticsearch.transport.TransportResponse;
import org.elasticsearch.transport.TransportResponse.Empty;
import org.elasticsearch.transport.TransportResponseHandler;
import org.elasticsearch.transport.TransportService;

import java.io.IOException;
import java.util.Map;
import java.util.Objects;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Base class for requests that should be executed on a primary copy followed by replica copies.
 * Subclasses can resolve the target shard and provide implementation for primary and replica operations.
 *
 * The action samples cluster state on the receiving node to reroute to node with primary copy and on the
 * primary node to validate request before primary operation followed by sampling state again for resolving
 * nodes with replica copies to perform replication.
 */
public abstract class TransportReplicationAction<
            Request extends ReplicationRequest<Request>,
            ReplicaRequest extends ReplicationRequest<ReplicaRequest>,
            Response extends ReplicationResponse
        > extends TransportAction<Request, Response> {

    protected final ThreadPool threadPool;
    protected final TransportService transportService;
    protected final ClusterService clusterService;
    protected final ShardStateAction shardStateAction;
    protected final IndicesService indicesService;
    protected final IndexNameExpressionResolver indexNameExpressionResolver;
    protected final TransportRequestOptions transportOptions;
    protected final String executor;

    // package private for testing
    protected final String transportReplicaAction;
    protected final String transportPrimaryAction;

    private final boolean syncGlobalCheckpointAfterOperation;

    protected TransportReplicationAction(Settings settings, String actionName, TransportService transportService,
                                         ClusterService clusterService, IndicesService indicesService,
                                         ThreadPool threadPool, ShardStateAction shardStateAction,
                                         ActionFilters actionFilters,
                                         IndexNameExpressionResolver indexNameExpressionResolver, Writeable.Reader<Request> requestReader,
                                         Writeable.Reader<ReplicaRequest> replicaRequestReader, String executor) {
        this(settings, actionName, transportService, clusterService, indicesService, threadPool, shardStateAction, actionFilters,
                indexNameExpressionResolver, requestReader, replicaRequestReader, executor, false, false);
    }


    protected TransportReplicationAction(Settings settings, String actionName, TransportService transportService,
                                         ClusterService clusterService, IndicesService indicesService,
                                         ThreadPool threadPool, ShardStateAction shardStateAction,
                                         ActionFilters actionFilters,
                                         IndexNameExpressionResolver indexNameExpressionResolver, Writeable.Reader<Request> requestReader,
                                         Writeable.Reader<ReplicaRequest> replicaRequestReader, String executor,
                                         boolean syncGlobalCheckpointAfterOperation, boolean forceExecutionOnPrimary) {
        super(actionName, actionFilters, transportService.getTaskManager());
        this.threadPool = threadPool;
        this.transportService = transportService;
        this.clusterService = clusterService;
        this.indicesService = indicesService;
        this.shardStateAction = shardStateAction;
        this.indexNameExpressionResolver = indexNameExpressionResolver;
        this.executor = executor;

        this.transportPrimaryAction = actionName + "[p]";
        this.transportReplicaAction = actionName + "[r]";

        transportService.registerRequestHandler(actionName, ThreadPool.Names.SAME, requestReader, this::handleOperationRequest);

        transportService.registerRequestHandler(transportPrimaryAction, executor, forceExecutionOnPrimary, true,
            in -> new ConcreteShardRequest<>(requestReader, in), this::handlePrimaryRequest);

        // we must never reject on because of thread pool capacity on replicas
        transportService.registerRequestHandler(transportReplicaAction, executor, true, true,
            in -> new ConcreteReplicaRequest<>(replicaRequestReader, in), this::handleReplicaRequest);

        this.transportOptions = transportOptions(settings);

        this.syncGlobalCheckpointAfterOperation = syncGlobalCheckpointAfterOperation;
    }

    @Override
    protected void doExecute(Task task, Request request, ActionListener<Response> listener) {
        assert request.shardId() != null : "request shardId must be set";
        new ReroutePhase((ReplicationTask) task, request, listener).run();
    }

    protected ReplicationOperation.Replicas<ReplicaRequest> newReplicasProxy() {
        return new ReplicasProxy();
    }

    protected abstract Response newResponseInstance(StreamInput in) throws IOException;

    /**
     * Resolves derived values in the request. For example, the target shard id of the incoming request, if not set at request construction.
     * Additional processing or validation of the request should be done here.
     *
     * @param indexMetaData index metadata of the concrete index this request is going to operate on
     * @param request       the request to resolve
     */
    protected void resolveRequest(final IndexMetaData indexMetaData, final Request request) {
        if (request.waitForActiveShards() == ActiveShardCount.DEFAULT) {
            // if the wait for active shard count has not been set in the request,
            // resolve it from the index settings
            request.waitForActiveShards(indexMetaData.getWaitForActiveShards());
        }
    }

    /**
     * Primary operation on node with primary copy.
     *
     * @param shardRequest the request to the primary shard
     * @param primary      the primary shard to perform the operation on
     */
    protected abstract void shardOperationOnPrimary(Request shardRequest, IndexShard primary,
        ActionListener<PrimaryResult<ReplicaRequest, Response>> listener);

    /**
     * Synchronously execute the specified replica operation. This is done under a permit from
     * {@link IndexShard#acquireReplicaOperationPermit(long, long, long, ActionListener, String, Object)}.
     *
     * @param shardRequest the request to the replica shard
     * @param replica      the replica shard to perform the operation on
     */
    protected abstract ReplicaResult shardOperationOnReplica(ReplicaRequest shardRequest, IndexShard replica) throws Exception;

    /**
     * Cluster level block to check before request execution. Returning null means that no blocks need to be checked.
     */
    @Nullable
    protected ClusterBlockLevel globalBlockLevel() {
        return null;
    }

    /**
     * Index level block to check before request execution. Returning null means that no blocks need to be checked.
     */
    @Nullable
    public ClusterBlockLevel indexBlockLevel() {
        return null;
    }

    /**
     * True if provided index should be resolved when resolving request
     */
    protected boolean resolveIndex() {
        return true;
    }

    protected TransportRequestOptions transportOptions(Settings settings) {
        return TransportRequestOptions.EMPTY;
    }

    private String concreteIndex(final ClusterState state, final ReplicationRequest request) {
        return resolveIndex() ? indexNameExpressionResolver.concreteSingleIndex(state, request).getName() : request.index();
    }

    private ClusterBlockException blockExceptions(final ClusterState state, final String indexName) {
        ClusterBlockLevel globalBlockLevel = globalBlockLevel();
        if (globalBlockLevel != null) {
            ClusterBlockException blockException = state.blocks().globalBlockedException(globalBlockLevel);
            if (blockException != null) {
                return blockException;
            }
        }
        ClusterBlockLevel indexBlockLevel = indexBlockLevel();
        if (indexBlockLevel != null) {
            ClusterBlockException blockException = state.blocks().indexBlockedException(indexBlockLevel, indexName);
            if (blockException != null) {
                return blockException;
            }
        }
        return null;
    }

    protected boolean retryPrimaryException(final Throwable e) {
        return e.getClass() == ReplicationOperation.RetryOnPrimaryException.class
                || TransportActions.isShardNotAvailableException(e)
                || isRetryableClusterBlockException(e);
    }

    boolean isRetryableClusterBlockException(final Throwable e) {
        if (e instanceof ClusterBlockException) {
            return ((ClusterBlockException) e).retryable();
        }
        return false;
    }

    protected void handleOperationRequest(final Request request, final TransportChannel channel, Task task) {
        execute(task, request, new ChannelActionListener<>(channel, actionName, request));
    }

    protected void handlePrimaryRequest(final ConcreteShardRequest<Request> request, final TransportChannel channel, final Task task) {
        new AsyncPrimaryAction(
            request, new ChannelActionListener<>(channel, transportPrimaryAction, request), (ReplicationTask) task).run();
    }

    class AsyncPrimaryAction extends AbstractRunnable {
        private final ActionListener<Response> onCompletionListener;
        private final ReplicationTask replicationTask;
        private final ConcreteShardRequest<Request> primaryRequest;

        AsyncPrimaryAction(ConcreteShardRequest<Request> primaryRequest, ActionListener<Response> onCompletionListener,
                           ReplicationTask replicationTask) {
            this.primaryRequest = primaryRequest;
            this.onCompletionListener = onCompletionListener;
            this.replicationTask = replicationTask;
        }

        @Override
        protected void doRun() throws Exception {
            final ShardId shardId = primaryRequest.getRequest().shardId();
            final IndexShard indexShard = getIndexShard(shardId);
            final ShardRouting shardRouting = indexShard.routingEntry();
            // we may end up here if the cluster state used to route the primary is so stale that the underlying
            // index shard was replaced with a replica. For example - in a two node cluster, if the primary fails
            // the replica will take over and a replica will be assigned to the first node.
            if (shardRouting.primary() == false) {
                throw new ReplicationOperation.RetryOnPrimaryException(shardId, "actual shard is not a primary " + shardRouting);
            }
            final String actualAllocationId = shardRouting.allocationId().getId();
            if (actualAllocationId.equals(primaryRequest.getTargetAllocationID()) == false) {
                throw new ShardNotFoundException(shardId, "expected allocation id [{}] but found [{}]",
                    primaryRequest.getTargetAllocationID(), actualAllocationId);
            }
            final long actualTerm = indexShard.getPendingPrimaryTerm();
            if (actualTerm != primaryRequest.getPrimaryTerm()) {
                throw new ShardNotFoundException(shardId, "expected allocation id [{}] with term [{}] but found [{}]",
                    primaryRequest.getTargetAllocationID(), primaryRequest.getPrimaryTerm(), actualTerm);
            }

            acquirePrimaryOperationPermit(
                    indexShard,
                    primaryRequest.getRequest(),
                    ActionListener.wrap(
                            releasable -> runWithPrimaryShardReference(new PrimaryShardReference(indexShard, releasable)),
                            e -> {
                                if (e instanceof ShardNotInPrimaryModeException) {
                                    onFailure(new ReplicationOperation.RetryOnPrimaryException(shardId, "shard is not in primary mode", e));
                                } else {
                                    onFailure(e);
                                }
                            }));
        }

        void runWithPrimaryShardReference(final PrimaryShardReference primaryShardReference) {
            try {
                final ClusterState clusterState = clusterService.state();
                final IndexMetaData indexMetaData = clusterState.metaData().getIndexSafe(primaryShardReference.routingEntry().index());

                final ClusterBlockException blockException = blockExceptions(clusterState, indexMetaData.getIndex().getName());
                if (blockException != null) {
                    logger.trace("cluster is blocked, action failed on primary", blockException);
                    throw blockException;
                }

                if (primaryShardReference.isRelocated()) {
                    primaryShardReference.close(); // release shard operation lock as soon as possible
                    setPhase(replicationTask, "primary_delegation");
                    // delegate primary phase to relocation target
                    // it is safe to execute primary phase on relocation target as there are no more in-flight operations where primary
                    // phase is executed on local shard and all subsequent operations are executed on relocation target as primary phase.
                    final ShardRouting primary = primaryShardReference.routingEntry();
                    assert primary.relocating() : "indexShard is marked as relocated but routing isn't" + primary;
                    final Writeable.Reader<Response> reader = TransportReplicationAction.this::newResponseInstance;
                    DiscoveryNode relocatingNode = clusterState.nodes().get(primary.relocatingNodeId());
                    transportService.sendRequest(relocatingNode, transportPrimaryAction,
                        new ConcreteShardRequest<>(primaryRequest.getRequest(), primary.allocationId().getRelocationId(),
                            primaryRequest.getPrimaryTerm()),
                        transportOptions,
                        new ActionListenerResponseHandler<>(onCompletionListener, reader) {
                            @Override
                            public void handleResponse(Response response) {
                                setPhase(replicationTask, "finished");
                                super.handleResponse(response);
                            }

                            @Override
                            public void handleException(TransportException exp) {
                                setPhase(replicationTask, "finished");
                                super.handleException(exp);
                            }
                        });
                } else {
                    setPhase(replicationTask, "primary");

                    final ActionListener<Response> referenceClosingListener = ActionListener.wrap(response -> {
                        primaryShardReference.close(); // release shard operation lock before responding to caller
                        setPhase(replicationTask, "finished");
                        onCompletionListener.onResponse(response);
                    }, e -> handleException(primaryShardReference, e));

                    final ActionListener<Response> globalCheckpointSyncingListener = ActionListener.wrap(response -> {
                        if (syncGlobalCheckpointAfterOperation) {
                            final IndexShard shard = primaryShardReference.indexShard;
                            try {
                                shard.maybeSyncGlobalCheckpoint("post-operation");
                            } catch (final Exception e) {
                                // only log non-closed exceptions
                                if (ExceptionsHelper.unwrap(
                                    e, AlreadyClosedException.class, IndexShardClosedException.class) == null) {
                                    // intentionally swallow, a missed global checkpoint sync should not fail this operation
                                    logger.info(
                                        new ParameterizedMessage(
                                            "{} failed to execute post-operation global checkpoint sync", shard.shardId()), e);
                                }
                            }
                        }
                        referenceClosingListener.onResponse(response);
                    }, referenceClosingListener::onFailure);

                    new ReplicationOperation<>(primaryRequest.getRequest(), primaryShardReference,
                        ActionListener.wrap(result -> result.respond(globalCheckpointSyncingListener), referenceClosingListener::onFailure),
                        newReplicasProxy(), logger, actionName, primaryRequest.getPrimaryTerm()).execute();
                }
            } catch (Exception e) {
                handleException(primaryShardReference, e);
            }
        }

        private void handleException(PrimaryShardReference primaryShardReference, Exception e) {
            Releasables.closeWhileHandlingException(primaryShardReference); // release shard operation lock before responding to caller
            onFailure(e);
        }

        @Override
        public void onFailure(Exception e) {
            setPhase(replicationTask, "finished");
            onCompletionListener.onFailure(e);
        }

    }

    public static class PrimaryResult<ReplicaRequest extends ReplicationRequest<ReplicaRequest>,
            Response extends ReplicationResponse>
            implements ReplicationOperation.PrimaryResult<ReplicaRequest> {
        final ReplicaRequest replicaRequest;
        public final Response finalResponseIfSuccessful;
        public final Exception finalFailure;

        /**
         * Result of executing a primary operation
         * expects <code>finalResponseIfSuccessful</code> or <code>finalFailure</code> to be not-null
         */
        public PrimaryResult(ReplicaRequest replicaRequest, Response finalResponseIfSuccessful, Exception finalFailure) {
            assert finalFailure != null ^ finalResponseIfSuccessful != null
                    : "either a response or a failure has to be not null, " +
                    "found [" + finalFailure + "] failure and ["+ finalResponseIfSuccessful + "] response";
            this.replicaRequest = replicaRequest;
            this.finalResponseIfSuccessful = finalResponseIfSuccessful;
            this.finalFailure = finalFailure;
        }

        public PrimaryResult(ReplicaRequest replicaRequest, Response replicationResponse) {
            this(replicaRequest, replicationResponse, null);
        }

        @Override
        public ReplicaRequest replicaRequest() {
            return replicaRequest;
        }

        @Override
        public void setShardInfo(ReplicationResponse.ShardInfo shardInfo) {
            if (finalResponseIfSuccessful != null) {
                finalResponseIfSuccessful.setShardInfo(shardInfo);
            }
        }

        public void respond(ActionListener<Response> listener) {
            if (finalResponseIfSuccessful != null) {
                listener.onResponse(finalResponseIfSuccessful);
            } else {
                listener.onFailure(finalFailure);
            }
        }
    }

    public static class ReplicaResult {
        final Exception finalFailure;

        public ReplicaResult(Exception finalFailure) {
            this.finalFailure = finalFailure;
        }

        public ReplicaResult() {
            this(null);
        }

        public void respond(ActionListener<TransportResponse.Empty> listener) {
            if (finalFailure == null) {
                listener.onResponse(TransportResponse.Empty.INSTANCE);
            } else {
                listener.onFailure(finalFailure);
            }
        }
    }

    protected void handleReplicaRequest(final ConcreteReplicaRequest<ReplicaRequest> replicaRequest,
                                        final TransportChannel channel, final Task task) {
        new AsyncReplicaAction(
            replicaRequest, new ChannelActionListener<>(channel, transportReplicaAction, replicaRequest), (ReplicationTask) task).run();
    }

    public static class RetryOnReplicaException extends ElasticsearchException {

        public RetryOnReplicaException(ShardId shardId, String msg) {
            super(msg);
            setShard(shardId);
        }

        public RetryOnReplicaException(StreamInput in) throws IOException {
            super(in);
        }
    }

    private final class AsyncReplicaAction extends AbstractRunnable implements ActionListener<Releasable> {
        private final ActionListener<ReplicaResponse> onCompletionListener;
        private final IndexShard replica;
        /**
         * The task on the node with the replica shard.
         */
        private final ReplicationTask task;
        // important: we pass null as a timeout as failing a replica is
        // something we want to avoid at all costs
        private final ClusterStateObserver observer = new ClusterStateObserver(clusterService, null, logger, threadPool.getThreadContext());
        private final ConcreteReplicaRequest<ReplicaRequest> replicaRequest;

        AsyncReplicaAction(ConcreteReplicaRequest<ReplicaRequest> replicaRequest, ActionListener<ReplicaResponse> onCompletionListener,
                           ReplicationTask task) {
            this.replicaRequest = replicaRequest;
            this.onCompletionListener = onCompletionListener;
            this.task = task;
            final ShardId shardId = replicaRequest.getRequest().shardId();
            assert shardId != null : "request shardId must be set";
            this.replica = getIndexShard(shardId);
        }

        @Override
        public void onResponse(Releasable releasable) {
            try {
                assert replica.getActiveOperationsCount() != 0 : "must perform shard operation under a permit";
                final ReplicaResult replicaResult = shardOperationOnReplica(replicaRequest.getRequest(), replica);
                releasable.close(); // release shard operation lock before responding to caller
                final TransportReplicationAction.ReplicaResponse response =
                        new ReplicaResponse(replica.getLocalCheckpoint(), replica.getLastSyncedGlobalCheckpoint());
                replicaResult.respond(new ResponseListener(response));
            } catch (final Exception e) {
                Releasables.closeWhileHandlingException(releasable); // release shard operation lock before responding to caller
                AsyncReplicaAction.this.onFailure(e);
            }
        }

        @Override
        public void onFailure(Exception e) {
            if (e instanceof RetryOnReplicaException) {
                logger.trace(
                        () -> new ParameterizedMessage(
                            "Retrying operation on replica, action [{}], request [{}]",
                            transportReplicaAction,
                            replicaRequest.getRequest()),
                    e);
                replicaRequest.getRequest().onRetry();
                observer.waitForNextChange(new ClusterStateObserver.Listener() {
                    @Override
                    public void onNewClusterState(ClusterState state) {
                        // Forking a thread on local node via transport service so that custom transport service have an
                        // opportunity to execute custom logic before the replica operation begins
                        transportService.sendRequest(clusterService.localNode(), transportReplicaAction,
                            replicaRequest,
                            new ActionListenerResponseHandler<>(onCompletionListener, ReplicaResponse::new));
                    }

                    @Override
                    public void onClusterServiceClose() {
                        responseWithFailure(new NodeClosedException(clusterService.localNode()));
                    }

                    @Override
                    public void onTimeout(TimeValue timeout) {
                        throw new AssertionError("Cannot happen: there is not timeout");
                    }
                });
            } else {
                responseWithFailure(e);
            }
        }

        protected void responseWithFailure(Exception e) {
            setPhase(task, "finished");
            onCompletionListener.onFailure(e);
        }

        @Override
        protected void doRun() throws Exception {
            setPhase(task, "replica");
            final String actualAllocationId = this.replica.routingEntry().allocationId().getId();
            if (actualAllocationId.equals(replicaRequest.getTargetAllocationID()) == false) {
                throw new ShardNotFoundException(this.replica.shardId(), "expected allocation id [{}] but found [{}]",
                    replicaRequest.getTargetAllocationID(), actualAllocationId);
            }
            acquireReplicaOperationPermit(replica, replicaRequest.getRequest(), this, replicaRequest.getPrimaryTerm(),
                replicaRequest.getGlobalCheckpoint(), replicaRequest.getMaxSeqNoOfUpdatesOrDeletes());
        }

        /**
         * Listens for the response on the replica and sends the response back to the primary.
         */
        private class ResponseListener implements ActionListener<TransportResponse.Empty> {
            private final ReplicaResponse replicaResponse;

            ResponseListener(ReplicaResponse replicaResponse) {
                this.replicaResponse = replicaResponse;
            }

            @Override
            public void onResponse(Empty response) {
                if (logger.isTraceEnabled()) {
                    logger.trace("action [{}] completed on shard [{}] for request [{}]", transportReplicaAction,
                        replicaRequest.getRequest().shardId(),
                        replicaRequest.getRequest());
                }
                setPhase(task, "finished");
                onCompletionListener.onResponse(replicaResponse);
            }

            @Override
            public void onFailure(Exception e) {
                responseWithFailure(e);
            }
        }
    }

    private IndexShard getIndexShard(final ShardId shardId) {
        IndexService indexService = indicesService.indexServiceSafe(shardId.getIndex());
        return indexService.getShard(shardId.id());
    }

    /**
     * Responsible for routing and retrying failed operations on the primary.
     * The actual primary operation is done in {@link ReplicationOperation} on the
     * node with primary copy.
     *
     * Resolves index and shard id for the request before routing it to target node
     */
    final class ReroutePhase extends AbstractRunnable {
        private final ActionListener<Response> listener;
        private final Request request;
        private final ReplicationTask task;
        private final ClusterStateObserver observer;
        private final AtomicBoolean finished = new AtomicBoolean();

        ReroutePhase(ReplicationTask task, Request request, ActionListener<Response> listener) {
            this.request = request;
            if (task != null) {
                this.request.setParentTask(clusterService.localNode().getId(), task.getId());
            }
            this.listener = listener;
            this.task = task;
            this.observer = new ClusterStateObserver(clusterService, request.timeout(), logger, threadPool.getThreadContext());
        }

        @Override
        public void onFailure(Exception e) {
            finishWithUnexpectedFailure(e);
        }

        @Override
        protected void doRun() {
            setPhase(task, "routing");
            final ClusterState state = observer.setAndGetObservedState();
            final String concreteIndex = concreteIndex(state, request);
            final ClusterBlockException blockException = blockExceptions(state, concreteIndex);
            if (blockException != null) {
                if (blockException.retryable()) {
                    logger.trace("cluster is blocked, scheduling a retry", blockException);
                    retry(blockException);
                } else {
                    finishAsFailed(blockException);
                }
            } else {
                // request does not have a shardId yet, we need to pass the concrete index to resolve shardId
                final IndexMetaData indexMetaData = state.metaData().index(concreteIndex);
                if (indexMetaData == null) {
                    retry(new IndexNotFoundException(concreteIndex));
                    return;
                }
                if (indexMetaData.getState() == IndexMetaData.State.CLOSE) {
                    throw new IndexClosedException(indexMetaData.getIndex());
                }

                // resolve all derived request fields, so we can route and apply it
                resolveRequest(indexMetaData, request);
                assert request.waitForActiveShards() != ActiveShardCount.DEFAULT :
                    "request waitForActiveShards must be set in resolveRequest";

                final ShardRouting primary = primary(state);
                if (retryIfUnavailable(state, primary)) {
                    return;
                }
                final DiscoveryNode node = state.nodes().get(primary.currentNodeId());
                if (primary.currentNodeId().equals(state.nodes().getLocalNodeId())) {
                    performLocalAction(state, primary, node, indexMetaData);
                } else {
                    performRemoteAction(state, primary, node);
                }
            }
        }

        private void performLocalAction(ClusterState state, ShardRouting primary, DiscoveryNode node, IndexMetaData indexMetaData) {
            setPhase(task, "waiting_on_primary");
            if (logger.isTraceEnabled()) {
                logger.trace("send action [{}] to local primary [{}] for request [{}] with cluster state version [{}] to [{}] ",
                    transportPrimaryAction, request.shardId(), request, state.version(), primary.currentNodeId());
            }
            performAction(node, transportPrimaryAction, true,
                new ConcreteShardRequest<>(request, primary.allocationId().getId(), indexMetaData.primaryTerm(primary.id())));
        }

        private void performRemoteAction(ClusterState state, ShardRouting primary, DiscoveryNode node) {
            if (state.version() < request.routedBasedOnClusterVersion()) {
                logger.trace("failed to find primary [{}] for request [{}] despite sender thinking it would be here. Local cluster state "
                        + "version [{}]] is older than on sending node (version [{}]), scheduling a retry...", request.shardId(), request,
                    state.version(), request.routedBasedOnClusterVersion());
                retryBecauseUnavailable(request.shardId(), "failed to find primary as current cluster state with version ["
                    + state.version() + "] is stale (expected at least [" + request.routedBasedOnClusterVersion() + "]");
                return;
            } else {
                // chasing the node with the active primary for a second hop requires that we are at least up-to-date with the current
                // cluster state version this prevents redirect loops between two nodes when a primary was relocated and the relocation
                // target is not aware that it is the active primary shard already.
                request.routedBasedOnClusterVersion(state.version());
            }
            if (logger.isTraceEnabled()) {
                logger.trace("send action [{}] on primary [{}] for request [{}] with cluster state version [{}] to [{}]", actionName,
                    request.shardId(), request, state.version(), primary.currentNodeId());
            }
            setPhase(task, "rerouted");
            performAction(node, actionName, false, request);
        }

        private boolean retryIfUnavailable(ClusterState state, ShardRouting primary) {
            if (primary == null || primary.active() == false) {
                logger.trace("primary shard [{}] is not yet active, scheduling a retry: action [{}], request [{}], "
                    + "cluster state version [{}]", request.shardId(), actionName, request, state.version());
                retryBecauseUnavailable(request.shardId(), "primary shard is not active");
                return true;
            }
            if (state.nodes().nodeExists(primary.currentNodeId()) == false) {
                logger.trace("primary shard [{}] is assigned to an unknown node [{}], scheduling a retry: action [{}], request [{}], "
                    + "cluster state version [{}]", request.shardId(), primary.currentNodeId(), actionName, request, state.version());
                retryBecauseUnavailable(request.shardId(), "primary shard isn't assigned to a known node.");
                return true;
            }
            return false;
        }

        private ShardRouting primary(ClusterState state) {
            IndexShardRoutingTable indexShard = state.getRoutingTable().shardRoutingTable(request.shardId());
            return indexShard.primaryShard();
        }

        private void performAction(final DiscoveryNode node, final String action, final boolean isPrimaryAction,
                                   final TransportRequest requestToPerform) {
            transportService.sendRequest(node, action, requestToPerform, transportOptions, new TransportResponseHandler<Response>() {

                @Override
                public Response read(StreamInput in) throws IOException {
                    return newResponseInstance(in);
                }

                @Override
                public String executor() {
                    return ThreadPool.Names.SAME;
                }

                @Override
                public void handleResponse(Response response) {
                    finishOnSuccess(response);
                }

                @Override
                public void handleException(TransportException exp) {
                    try {
                        // if we got disconnected from the node, or the node / shard is not in the right state (being closed)
                        final Throwable cause = exp.unwrapCause();
                        if (cause instanceof ConnectTransportException || cause instanceof NodeClosedException ||
                            (isPrimaryAction && retryPrimaryException(cause))) {
                            logger.trace(() -> new ParameterizedMessage(
                                    "received an error from node [{}] for request [{}], scheduling a retry",
                                    node.getId(), requestToPerform), exp);
                            retry(exp);
                        } else {
                            finishAsFailed(exp);
                        }
                    } catch (Exception e) {
                        e.addSuppressed(exp);
                        finishWithUnexpectedFailure(e);
                    }
                }
            });
        }

        void retry(Exception failure) {
            assert failure != null;
            if (observer.isTimedOut()) {
                // we running as a last attempt after a timeout has happened. don't retry
                finishAsFailed(failure);
                return;
            }
            setPhase(task, "waiting_for_retry");
            request.onRetry();
            observer.waitForNextChange(new ClusterStateObserver.Listener() {
                @Override
                public void onNewClusterState(ClusterState state) {
                    run();
                }

                @Override
                public void onClusterServiceClose() {
                    finishAsFailed(new NodeClosedException(clusterService.localNode()));
                }

                @Override
                public void onTimeout(TimeValue timeout) {
                    // Try one more time...
                    run();
                }
            });
        }

        void finishAsFailed(Exception failure) {
            if (finished.compareAndSet(false, true)) {
                setPhase(task, "failed");
                logger.trace(() -> new ParameterizedMessage("operation failed. action [{}], request [{}]", actionName, request), failure);
                listener.onFailure(failure);
            } else {
                assert false : "finishAsFailed called but operation is already finished";
            }
        }

        void finishWithUnexpectedFailure(Exception failure) {
            logger.warn(() -> new ParameterizedMessage(
                        "unexpected error during the primary phase for action [{}], request [{}]",
                        actionName, request), failure);
            if (finished.compareAndSet(false, true)) {
                setPhase(task, "failed");
                listener.onFailure(failure);
            } else {
                assert false : "finishWithUnexpectedFailure called but operation is already finished";
            }
        }

        void finishOnSuccess(Response response) {
            if (finished.compareAndSet(false, true)) {
                setPhase(task, "finished");
                if (logger.isTraceEnabled()) {
                    logger.trace("operation succeeded. action [{}],request [{}]", actionName, request);
                }
                listener.onResponse(response);
            } else {
                assert false : "finishOnSuccess called but operation is already finished";
            }
        }

        void retryBecauseUnavailable(ShardId shardId, String message) {
            retry(new UnavailableShardsException(shardId, "{} Timeout: [{}], request: [{}]", message, request.timeout(), request));
        }
    }

    /**
     * Executes the logic for acquiring one or more operation permit on a primary shard. The default is to acquire a single permit but this
     * method can be overridden to acquire more.
     */
    protected void acquirePrimaryOperationPermit(final IndexShard primary,
                                                 final Request request,
                                                 final ActionListener<Releasable> onAcquired) {
        primary.acquirePrimaryOperationPermit(onAcquired, executor, request);
    }

    /**
     * Executes the logic for acquiring one or more operation permit on a replica shard. The default is to acquire a single permit but this
     * method can be overridden to acquire more.
     */
    protected void acquireReplicaOperationPermit(final IndexShard replica,
                                                 final ReplicaRequest request,
                                                 final ActionListener<Releasable> onAcquired,
                                                 final long primaryTerm,
                                                 final long globalCheckpoint,
                                                 final long maxSeqNoOfUpdatesOrDeletes) {
        replica.acquireReplicaOperationPermit(primaryTerm, globalCheckpoint, maxSeqNoOfUpdatesOrDeletes, onAcquired, executor, request);
    }

    class PrimaryShardReference implements Releasable,
            ReplicationOperation.Primary<Request, ReplicaRequest, PrimaryResult<ReplicaRequest, Response>> {

        protected final IndexShard indexShard;
        private final Releasable operationLock;

        PrimaryShardReference(IndexShard indexShard, Releasable operationLock) {
            this.indexShard = indexShard;
            this.operationLock = operationLock;
        }

        @Override
        public void close() {
            operationLock.close();
        }

        public ShardRouting routingEntry() {
            return indexShard.routingEntry();
        }

        public boolean isRelocated() {
            return indexShard.isRelocatedPrimary();
        }

        @Override
        public void failShard(String reason, Exception e) {
            try {
                indexShard.failShard(reason, e);
            } catch (Exception inner) {
                e.addSuppressed(inner);
            }
        }

        @Override
        public void perform(Request request, ActionListener<PrimaryResult<ReplicaRequest, Response>> listener) {
            if (Assertions.ENABLED) {
                listener = ActionListener.map(listener, result -> {
                    assert result.replicaRequest() == null || result.finalFailure == null : "a replica request [" + result.replicaRequest()
                        + "] with a primary failure [" + result.finalFailure + "]";
                    return result;
                });
            }
            assert indexShard.getActiveOperationsCount() != 0 : "must perform shard operation under a permit";
            shardOperationOnPrimary(request, indexShard, listener);
        }

        @Override
        public void updateLocalCheckpointForShard(String allocationId, long checkpoint) {
            indexShard.updateLocalCheckpointForShard(allocationId, checkpoint);
        }

        @Override
        public void updateGlobalCheckpointForShard(final String allocationId, final long globalCheckpoint) {
            indexShard.updateGlobalCheckpointForShard(allocationId, globalCheckpoint);
        }

        @Override
        public long localCheckpoint() {
            return indexShard.getLocalCheckpoint();
        }

        @Override
        public long globalCheckpoint() {
            return indexShard.getLastSyncedGlobalCheckpoint();
        }

        @Override
        public long computedGlobalCheckpoint() {
            return indexShard.getLastKnownGlobalCheckpoint();
        }

        @Override
        public long maxSeqNoOfUpdatesOrDeletes() {
            return indexShard.getMaxSeqNoOfUpdatesOrDeletes();
        }

        @Override
        public ReplicationGroup getReplicationGroup() {
            return indexShard.getReplicationGroup();
        }
    }


    public static class ReplicaResponse extends ActionResponse implements ReplicationOperation.ReplicaResponse {
        private long localCheckpoint;
        private long globalCheckpoint;

        ReplicaResponse(StreamInput in) throws IOException {
            super(in);
            localCheckpoint = in.readZLong();
            globalCheckpoint = in.readZLong();
        }

        public ReplicaResponse(long localCheckpoint, long globalCheckpoint) {
            /*
             * A replica should always know its own local checkpoints so this should always be a valid sequence number or the pre-6.0
             * checkpoint value when simulating responses to replication actions that pre-6.0 nodes are not aware of (e.g., the global
             * checkpoint background sync, and the primary/replica resync).
             */
            assert localCheckpoint != SequenceNumbers.UNASSIGNED_SEQ_NO;
            this.localCheckpoint = localCheckpoint;
            this.globalCheckpoint = globalCheckpoint;
        }

        @Override
        public void writeTo(StreamOutput out) throws IOException {
            out.writeZLong(localCheckpoint);
            out.writeZLong(globalCheckpoint);
        }

        @Override
        public long localCheckpoint() {
            return localCheckpoint;
        }

        @Override
        public long globalCheckpoint() {
            return globalCheckpoint;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            ReplicaResponse that = (ReplicaResponse) o;
            return localCheckpoint == that.localCheckpoint &&
                globalCheckpoint == that.globalCheckpoint;
        }

        @Override
        public int hashCode() {
            return Objects.hash(localCheckpoint, globalCheckpoint);
        }
    }

    /**
     * The {@code ReplicasProxy} is an implementation of the {@code Replicas}
     * interface that performs the actual {@code ReplicaRequest} on the replica
     * shards. It also encapsulates the logic required for failing the replica
     * if deemed necessary as well as marking it as stale when needed.
     */
    protected class ReplicasProxy implements ReplicationOperation.Replicas<ReplicaRequest> {

        @Override
        public void performOn(
                final ShardRouting replica,
                final ReplicaRequest request,
                final long primaryTerm,
                final long globalCheckpoint,
                final long maxSeqNoOfUpdatesOrDeletes,
                final ActionListener<ReplicationOperation.ReplicaResponse> listener) {
            String nodeId = replica.currentNodeId();
            final DiscoveryNode node = clusterService.state().nodes().get(nodeId);
            if (node == null) {
                listener.onFailure(new NoNodeAvailableException("unknown node [" + nodeId + "]"));
                return;
            }
            final ConcreteReplicaRequest<ReplicaRequest> replicaRequest = new ConcreteReplicaRequest<>(
                request, replica.allocationId().getId(), primaryTerm, globalCheckpoint, maxSeqNoOfUpdatesOrDeletes);
            final ActionListenerResponseHandler<ReplicaResponse> handler = new ActionListenerResponseHandler<>(listener,
                ReplicaResponse::new);
            transportService.sendRequest(node, transportReplicaAction, replicaRequest, transportOptions, handler);
        }

        @Override
        public void failShardIfNeeded(ShardRouting replica, long primaryTerm, String message, Exception exception,
                                      ActionListener<Void> listener) {
            // This does not need to fail the shard. The idea is that this
            // is a non-write operation (something like a refresh or a global
            // checkpoint sync) and therefore the replica should still be
            // "alive" if it were to fail.
            listener.onResponse(null);
        }

        @Override
        public void markShardCopyAsStaleIfNeeded(ShardId shardId, String allocationId, long primaryTerm, ActionListener<Void> listener) {
            // This does not need to make the shard stale. The idea is that this
            // is a non-write operation (something like a refresh or a global
            // checkpoint sync) and therefore the replica should still be
            // "alive" if it were to be marked as stale.
            listener.onResponse(null);
        }
    }

    /** a wrapper class to encapsulate a request when being sent to a specific allocation id **/
    public static class ConcreteShardRequest<R extends TransportRequest> extends TransportRequest {

        /** {@link AllocationId#getId()} of the shard this request is sent to **/
        private final String targetAllocationID;
        private final long primaryTerm;
        private final R request;

        public ConcreteShardRequest(Writeable.Reader<R> requestReader, StreamInput in) throws IOException {
            targetAllocationID = in.readString();
            primaryTerm  = in.readVLong();
            request = requestReader.read(in);
        }

        public ConcreteShardRequest(R request, String targetAllocationID, long primaryTerm) {
            Objects.requireNonNull(request);
            Objects.requireNonNull(targetAllocationID);
            this.request = request;
            this.targetAllocationID = targetAllocationID;
            this.primaryTerm = primaryTerm;
        }

        @Override
        public void setParentTask(String parentTaskNode, long parentTaskId) {
            request.setParentTask(parentTaskNode, parentTaskId);
        }

        @Override
        public void setParentTask(TaskId taskId) {
            request.setParentTask(taskId);
        }

        @Override
        public TaskId getParentTask() {
            return request.getParentTask();
        }
        @Override
        public Task createTask(long id, String type, String action, TaskId parentTaskId, Map<String, String> headers) {
            return request.createTask(id, type, action, parentTaskId, headers);
        }

        @Override
        public String getDescription() {
            return "[" + request.getDescription() + "] for aID [" + targetAllocationID + "] and term [" + primaryTerm + "]";
        }

        @Override
        public void writeTo(StreamOutput out) throws IOException {
            out.writeString(targetAllocationID);
            out.writeVLong(primaryTerm);
            request.writeTo(out);
        }

        public R getRequest() {
            return request;
        }

        public String getTargetAllocationID() {
            return targetAllocationID;
        }

        public long getPrimaryTerm() {
            return primaryTerm;
        }

        @Override
        public String toString() {
            return "request: " + request + ", target allocation id: " + targetAllocationID + ", primary term: " + primaryTerm;
        }
    }

    protected static final class ConcreteReplicaRequest<R extends TransportRequest> extends ConcreteShardRequest<R> {

        private final long globalCheckpoint;
        private final long maxSeqNoOfUpdatesOrDeletes;

        public ConcreteReplicaRequest(Writeable.Reader<R> requestReader, StreamInput in) throws IOException {
            super(requestReader, in);
            globalCheckpoint = in.readZLong();
            maxSeqNoOfUpdatesOrDeletes = in.readZLong();
        }

        public ConcreteReplicaRequest(final R request, final String targetAllocationID, final long primaryTerm,
                                      final long globalCheckpoint, final long maxSeqNoOfUpdatesOrDeletes) {
            super(request, targetAllocationID, primaryTerm);
            this.globalCheckpoint = globalCheckpoint;
            this.maxSeqNoOfUpdatesOrDeletes = maxSeqNoOfUpdatesOrDeletes;
        }

        @Override
        public void writeTo(StreamOutput out) throws IOException {
            super.writeTo(out);
            out.writeZLong(globalCheckpoint);
            out.writeZLong(maxSeqNoOfUpdatesOrDeletes);
        }

        public long getGlobalCheckpoint() {
            return globalCheckpoint;
        }

        public long getMaxSeqNoOfUpdatesOrDeletes() {
            return maxSeqNoOfUpdatesOrDeletes;
        }

        @Override
        public String toString() {
            return "ConcreteReplicaRequest{" +
                    "targetAllocationID='" + getTargetAllocationID() + '\'' +
                    ", primaryTerm='" + getPrimaryTerm() + '\'' +
                    ", request=" + getRequest() +
                    ", globalCheckpoint=" + globalCheckpoint +
                    ", maxSeqNoOfUpdatesOrDeletes=" + maxSeqNoOfUpdatesOrDeletes +
                    '}';
        }
    }

    /**
     * Sets the current phase on the task if it isn't null. Pulled into its own
     * method because its more convenient that way.
     */
    static void setPhase(ReplicationTask task, String phase) {
        if (task != null) {
            task.setPhase(phase);
        }
    }
}