Merge remote-tracking branch 'dakrone/add-store-status-to-explain'

core/src/main/java/org/elasticsearch/action/admin/cluster/allocation/ClusterAllocationExplanation.java

@@ -21,7 +21,6 @@ package org.elasticsearch.action.admin.cluster.allocation;
 
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.routing.UnassignedInfo;
-import org.elasticsearch.cluster.routing.allocation.decider.Decision;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -32,7 +31,6 @@ import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.index.shard.ShardId;
 
 import java.io.IOException;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -45,21 +43,18 @@ public final class ClusterAllocationExplanation implements ToXContent, Writeable
     private final ShardId shard;
     private final boolean primary;
     private final String assignedNodeId;
-    private final Map<DiscoveryNode, Decision> nodeToDecision;
-    private final Map<DiscoveryNode, Float> nodeWeights;
     private final UnassignedInfo unassignedInfo;
-    private final long remainingDelayNanos;
+    private final long remainingDelayMillis;
+    private final Map<DiscoveryNode, NodeExplanation> nodeExplanations;
 
-    public ClusterAllocationExplanation(ShardId shard, boolean primary, @Nullable String assignedNodeId,
-            UnassignedInfo unassignedInfo, Map<DiscoveryNode, Decision> nodeToDecision,
-            Map<DiscoveryNode, Float> nodeWeights, long remainingDelayNanos) {
+    public ClusterAllocationExplanation(ShardId shard, boolean primary, @Nullable String assignedNodeId, long remainingDelayMillis,
+                                        @Nullable UnassignedInfo unassignedInfo, Map<DiscoveryNode, NodeExplanation> nodeExplanations) {
         this.shard = shard;
         this.primary = primary;
         this.assignedNodeId = assignedNodeId;
         this.unassignedInfo = unassignedInfo;
-        this.nodeToDecision = nodeToDecision == null ? Collections.emptyMap() : nodeToDecision;
-        this.nodeWeights = nodeWeights == null ? Collections.emptyMap() : nodeWeights;
-        this.remainingDelayNanos = remainingDelayNanos;
+        this.remainingDelayMillis = remainingDelayMillis;
+        this.nodeExplanations = nodeExplanations;
     }
 
     public ClusterAllocationExplanation(StreamInput in) throws IOException {
@@ -67,27 +62,15 @@ public final class ClusterAllocationExplanation implements ToXContent, Writeable
         this.primary = in.readBoolean();
         this.assignedNodeId = in.readOptionalString();
         this.unassignedInfo = in.readOptionalWriteable(UnassignedInfo::new);
+        this.remainingDelayMillis = in.readVLong();
 
-        Map<DiscoveryNode, Decision> ntd = null;
-        int size = in.readVInt();
-        ntd = new HashMap<>(size);
-        for (int i = 0; i < size; i++) {
-            DiscoveryNode dn = new DiscoveryNode(in);
-            Decision decision = Decision.readFrom(in);
-            ntd.put(dn, decision);
+        int mapSize = in.readVInt();
+        Map<DiscoveryNode, NodeExplanation> nodeToExplanation = new HashMap<>(mapSize);
+        for (int i = 0; i < mapSize; i++) {
+            NodeExplanation nodeExplanation = new NodeExplanation(in);
+            nodeToExplanation.put(nodeExplanation.getNode(), nodeExplanation);
         }
-        this.nodeToDecision = ntd;
-
-        Map<DiscoveryNode, Float> ntw = null;
-        size = in.readVInt();
-        ntw = new HashMap<>(size);
-        for (int i = 0; i < size; i++) {
-            DiscoveryNode dn = new DiscoveryNode(in);
-            float weight = in.readFloat();
-            ntw.put(dn, weight);
-        }
-        this.nodeWeights = ntw;
-        remainingDelayNanos = in.readVLong();
+        this.nodeExplanations = nodeToExplanation;
     }
 
     @Override
@@ -96,27 +79,20 @@ public final class ClusterAllocationExplanation implements ToXContent, Writeable
         out.writeBoolean(this.isPrimary());
         out.writeOptionalString(this.getAssignedNodeId());
         out.writeOptionalWriteable(this.getUnassignedInfo());
+        out.writeVLong(remainingDelayMillis);
 
-        Map<DiscoveryNode, Decision> ntd = this.getNodeDecisions();
-        out.writeVInt(ntd.size());
-        for (Map.Entry<DiscoveryNode, Decision> entry : ntd.entrySet()) {
-            entry.getKey().writeTo(out);
-            Decision.writeTo(entry.getValue(), out);
-        }
-        Map<DiscoveryNode, Float> ntw = this.getNodeWeights();
-        out.writeVInt(ntw.size());
-        for (Map.Entry<DiscoveryNode, Float> entry : ntw.entrySet()) {
-            entry.getKey().writeTo(out);
-            out.writeFloat(entry.getValue());
+        out.writeVInt(this.nodeExplanations.size());
+        for (NodeExplanation explanation : this.nodeExplanations.values()) {
+            explanation.writeTo(out);
         }
-        out.writeVLong(remainingDelayNanos);
     }
 
-
+    /** Return the shard that the explanation is about */
     public ShardId getShard() {
         return this.shard;
     }
 
+    /** Return true if the explained shard is primary, false otherwise */
     public boolean isPrimary() {
         return this.primary;
     }
@@ -138,22 +114,14 @@ public final class ClusterAllocationExplanation implements ToXContent, Writeable
         return this.unassignedInfo;
     }
 
-    /** Return a map of node to decision for shard allocation */
-    public Map<DiscoveryNode, Decision> getNodeDecisions() {
-        return this.nodeToDecision;
-    }
-
-    /**
-     * Return a map of node to balancer "weight" for allocation. Higher weights mean the balancer wants to allocated the shard to that node
-     * more
-     */
-    public Map<DiscoveryNode, Float> getNodeWeights() {
-        return this.nodeWeights;
+    /** Return the remaining allocation delay for this shard in millisocends */
+    public long getRemainingDelayMillis() {
+        return this.remainingDelayMillis;
     }
 
-    /** Return the remaining allocation delay for this shard in nanoseconds */
-    public long getRemainingDelayNanos() {
-        return this.remainingDelayNanos;
+    /** Return a map of node to the explanation for that node */
+    public Map<DiscoveryNode, NodeExplanation> getNodeExplanations() {
+        return this.nodeExplanations;
     }
 
     public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
@@ -174,36 +142,118 @@ public final class ClusterAllocationExplanation implements ToXContent, Writeable
             if (unassignedInfo != null) {
                 unassignedInfo.toXContent(builder, params);
                 long delay = unassignedInfo.getLastComputedLeftDelayNanos();
-                builder.field("allocation_delay", TimeValue.timeValueNanos(delay));
-                builder.field("allocation_delay_ms", TimeValue.timeValueNanos(delay).millis());
-                builder.field("remaining_delay", TimeValue.timeValueNanos(remainingDelayNanos));
-                builder.field("remaining_delay_ms", TimeValue.timeValueNanos(remainingDelayNanos).millis());
+                builder.timeValueField("allocation_delay_in_millis", "allocation_delay", TimeValue.timeValueNanos(delay));
+                builder.timeValueField("remaining_delay_in_millis", "remaining_delay", TimeValue.timeValueMillis(remainingDelayMillis));
             }
             builder.startObject("nodes");
-            for (Map.Entry<DiscoveryNode, Float> entry : nodeWeights.entrySet()) {
-                DiscoveryNode node = entry.getKey();
-                builder.startObject(node.getId()); {
-                    builder.field("node_name", node.getName());
-                    builder.startObject("node_attributes"); {
-                        for (Map.Entry<String, String> attrEntry : node.getAttributes().entrySet()) {
-                            builder.field(attrEntry.getKey(), attrEntry.getValue());
-                        }
-                    }
-                    builder.endObject(); // end attributes
-                    Decision d = nodeToDecision.get(node);
-                    if (node.getId().equals(assignedNodeId)) {
-                        builder.field("final_decision", "CURRENTLY_ASSIGNED");
-                    } else {
-                        builder.field("final_decision", d.type().toString());
-                    }
-                    builder.field("weight", entry.getValue());
-                    d.toXContent(builder, params);
-                }
-                builder.endObject(); // end node <uuid>
+            for (NodeExplanation explanation : nodeExplanations.values()) {
+                explanation.toXContent(builder, params);
             }
             builder.endObject(); // end nodes
         }
         builder.endObject(); // end wrapping object
         return builder;
     }
+
+    /** An Enum representing the final decision for a shard allocation on a node */
+    public enum FinalDecision {
+        // Yes, the shard can be assigned
+        YES((byte) 0),
+        // No, the shard cannot be assigned
+        NO((byte) 1),
+        // The shard is already assigned to this node
+        ALREADY_ASSIGNED((byte) 2);
+
+        private final byte id;
+
+        FinalDecision (byte id) {
+            this.id = id;
+        }
+
+        private static FinalDecision fromId(byte id) {
+            switch (id) {
+                case 0: return YES;
+                case 1: return NO;
+                case 2: return ALREADY_ASSIGNED;
+                default:
+                    throw new IllegalArgumentException("unknown id for final decision: [" + id + "]");
+            }
+        }
+
+        @Override
+        public String toString() {
+            switch (id) {
+                case 0: return "YES";
+                case 1: return "NO";
+                case 2: return "ALREADY_ASSIGNED";
+                default:
+                    throw new IllegalArgumentException("unknown id for final decision: [" + id + "]");
+            }
+        }
+
+        static FinalDecision readFrom(StreamInput in) throws IOException {
+            return fromId(in.readByte());
+        }
+
+        void writeTo(StreamOutput out) throws IOException {
+            out.writeByte(id);
+        }
+    }
+
+    /** An Enum representing the state of the shard store's copy of the data on a node */
+    public enum StoreCopy {
+        // No data for this shard is on the node
+        NONE((byte) 0),
+        // A copy of the data is available on this node
+        AVAILABLE((byte) 1),
+        // The copy of the data on the node is corrupt
+        CORRUPT((byte) 2),
+        // There was an error reading this node's copy of the data
+        IO_ERROR((byte) 3),
+        // The copy of the data on the node is stale
+        STALE((byte) 4),
+        // It's unknown what the copy of the data is
+        UNKNOWN((byte) 5);
+
+        private final byte id;
+
+        StoreCopy (byte id) {
+            this.id = id;
+        }
+
+        private static StoreCopy fromId(byte id) {
+            switch (id) {
+                case 0: return NONE;
+                case 1: return AVAILABLE;
+                case 2: return CORRUPT;
+                case 3: return IO_ERROR;
+                case 4: return STALE;
+                case 5: return UNKNOWN;
+                default:
+                    throw new IllegalArgumentException("unknown id for store copy: [" + id + "]");
+            }
+        }
+
+        @Override
+        public String toString() {
+            switch (id) {
+                case 0: return "NONE";
+                case 1: return "AVAILABLE";
+                case 2: return "CORRUPT";
+                case 3: return "IO_ERROR";
+                case 4: return "STALE";
+                case 5: return "UNKNOWN";
+                default:
+                    throw new IllegalArgumentException("unknown id for store copy: [" + id + "]");
+            }
+        }
+
+        static StoreCopy readFrom(StreamInput in) throws IOException {
+            return fromId(in.readByte());
+        }
+
+        void writeTo(StreamOutput out) throws IOException {
+            out.writeByte(id);
+        }
+    }
 }

core/src/main/java/org/elasticsearch/action/admin/cluster/allocation/NodeExplanation.java

@@ -0,0 +1,145 @@
+/*
+ * 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.admin.cluster.allocation;
+
+import org.elasticsearch.ExceptionsHelper;
+import org.elasticsearch.action.admin.indices.shards.IndicesShardStoresResponse;
+import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.cluster.routing.allocation.decider.Decision;
+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.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContentBuilder;
+
+import java.io.IOException;
+import java.util.Map;
+/** The cluster allocation explanation for a single node */
+public class NodeExplanation implements Writeable, ToXContent {
+    private final DiscoveryNode node;
+    private final Decision nodeDecision;
+    private final Float nodeWeight;
+    private final IndicesShardStoresResponse.StoreStatus storeStatus;
+    private final ClusterAllocationExplanation.FinalDecision finalDecision;
+    private final ClusterAllocationExplanation.StoreCopy storeCopy;
+    private final String finalExplanation;
+
+    public NodeExplanation(final DiscoveryNode node, final Decision nodeDecision, final Float nodeWeight,
+                           final @Nullable IndicesShardStoresResponse.StoreStatus storeStatus,
+                           final ClusterAllocationExplanation.FinalDecision finalDecision,
+                           final String finalExplanation,
+                           final ClusterAllocationExplanation.StoreCopy storeCopy) {
+        this.node = node;
+        this.nodeDecision = nodeDecision;
+        this.nodeWeight = nodeWeight;
+        this.storeStatus = storeStatus;
+        this.finalDecision = finalDecision;
+        this.finalExplanation = finalExplanation;
+        this.storeCopy = storeCopy;
+    }
+
+    public NodeExplanation(StreamInput in) throws IOException {
+        this.node = new DiscoveryNode(in);
+        this.nodeDecision = Decision.readFrom(in);
+        this.nodeWeight = in.readFloat();
+        if (in.readBoolean()) {
+            this.storeStatus = IndicesShardStoresResponse.StoreStatus.readStoreStatus(in);
+        } else {
+            this.storeStatus = null;
+        }
+        this.finalDecision = ClusterAllocationExplanation.FinalDecision.readFrom(in);
+        this.finalExplanation = in.readString();
+        this.storeCopy = ClusterAllocationExplanation.StoreCopy.readFrom(in);
+    }
+
+    @Override
+    public void writeTo(StreamOutput out) throws IOException {
+        node.writeTo(out);
+        Decision.writeTo(nodeDecision, out);
+        out.writeFloat(nodeWeight);
+        if (storeStatus == null) {
+            out.writeBoolean(false);
+        } else {
+            out.writeBoolean(true);
+            storeStatus.writeTo(out);
+        }
+        finalDecision.writeTo(out);
+        out.writeString(finalExplanation);
+        storeCopy.writeTo(out);
+    }
+
+    public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
+        builder.startObject(node.getId()); {
+            builder.field("node_name", node.getName());
+            builder.startObject("node_attributes"); {
+                for (Map.Entry<String, String> attrEntry : node.getAttributes().entrySet()) {
+                    builder.field(attrEntry.getKey(), attrEntry.getValue());
+                }
+            }
+            builder.endObject(); // end attributes
+            builder.startObject("store"); {
+                builder.field("shard_copy", storeCopy.toString());
+                if (storeStatus != null) {
+                    final Throwable storeErr = storeStatus.getStoreException();
+                    if (storeErr != null) {
+                        builder.field("store_exception", ExceptionsHelper.detailedMessage(storeErr));
+                    }
+                }
+            }
+            builder.endObject(); // end store
+            builder.field("final_decision", finalDecision.toString());
+            builder.field("final_explanation", finalExplanation.toString());
+            builder.field("weight", nodeWeight);
+            nodeDecision.toXContent(builder, params);
+        }
+        builder.endObject(); // end node <uuid>
+        return builder;
+    }
+
+    public DiscoveryNode getNode() {
+        return this.node;
+    }
+
+    public Decision getDecision() {
+        return this.nodeDecision;
+    }
+
+    public Float getWeight() {
+        return this.nodeWeight;
+    }
+
+    @Nullable
+    public IndicesShardStoresResponse.StoreStatus getStoreStatus() {
+        return this.storeStatus;
+    }
+
+    public ClusterAllocationExplanation.FinalDecision getFinalDecision() {
+        return this.finalDecision;
+    }
+
+    public String getFinalExplanation() {
+        return this.finalExplanation;
+    }
+
+    public ClusterAllocationExplanation.StoreCopy getStoreCopy() {
+        return this.storeCopy;
+    }
+}

core/src/main/java/org/elasticsearch/action/admin/cluster/allocation/TransportClusterAllocationExplainAction.java

@@ -20,8 +20,13 @@
 package org.elasticsearch.action.admin.cluster.allocation;
 
 import com.carrotsearch.hppc.cursors.ObjectObjectCursor;
+import org.apache.lucene.index.CorruptIndexException;
 import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.ExceptionsHelper;
 import org.elasticsearch.action.ActionListener;
+import org.elasticsearch.action.admin.indices.shards.IndicesShardStoresRequest;
+import org.elasticsearch.action.admin.indices.shards.IndicesShardStoresResponse;
+import org.elasticsearch.action.admin.indices.shards.TransportIndicesShardStoresAction;
 import org.elasticsearch.action.support.ActionFilters;
 import org.elasticsearch.action.support.master.TransportMasterNodeAction;
 import org.elasticsearch.cluster.ClusterInfoService;
@@ -47,8 +52,10 @@ import org.elasticsearch.cluster.routing.allocation.allocator.ShardsAllocator;
 import org.elasticsearch.cluster.routing.allocation.decider.AllocationDeciders;
 import org.elasticsearch.cluster.routing.allocation.decider.Decision;
 import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.common.collect.ImmutableOpenIntMap;
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.TransportService;
 
@@ -56,6 +63,7 @@ import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 
 /**
  * The {@code TransportClusterAllocationExplainAction} is responsible for actually executing the explanation of a shard's allocation on the
@@ -68,19 +76,22 @@ public class TransportClusterAllocationExplainAction
     private final ClusterInfoService clusterInfoService;
     private final AllocationDeciders allocationDeciders;
     private final ShardsAllocator shardAllocator;
+    private final TransportIndicesShardStoresAction shardStoresAction;
 
     @Inject
     public TransportClusterAllocationExplainAction(Settings settings, TransportService transportService, ClusterService clusterService,
                                                    ThreadPool threadPool, ActionFilters actionFilters,
                                                    IndexNameExpressionResolver indexNameExpressionResolver,
                                                    AllocationService allocationService, ClusterInfoService clusterInfoService,
-                                                   AllocationDeciders allocationDeciders, ShardsAllocator shardAllocator) {
+                                                   AllocationDeciders allocationDeciders, ShardsAllocator shardAllocator,
+                                                   TransportIndicesShardStoresAction shardStoresAction) {
         super(settings, ClusterAllocationExplainAction.NAME, transportService, clusterService, threadPool, actionFilters,
                 indexNameExpressionResolver, ClusterAllocationExplainRequest::new);
         this.allocationService = allocationService;
         this.clusterInfoService = clusterInfoService;
         this.allocationDeciders = allocationDeciders;
         this.shardAllocator = shardAllocator;
+        this.shardStoresAction = shardStoresAction;
     }
 
     @Override
@@ -118,12 +129,86 @@ public class TransportClusterAllocationExplainAction
         }
     }
 
+    /**
+     * Construct a {@code NodeExplanation} object for the given shard given all the metadata. This also attempts to construct the human
+     * readable FinalDecision and final explanation as part of the explanation.
+     */
+    public static NodeExplanation calculateNodeExplanation(ShardRouting shard,
+                                                           IndexMetaData indexMetaData,
+                                                           DiscoveryNode node,
+                                                           Decision nodeDecision,
+                                                           Float nodeWeight,
+                                                           IndicesShardStoresResponse.StoreStatus storeStatus,
+                                                           String assignedNodeId,
+                                                           Set<String> activeAllocationIds) {
+        final ClusterAllocationExplanation.FinalDecision finalDecision;
+        final ClusterAllocationExplanation.StoreCopy storeCopy;
+        final String finalExplanation;
+
+        if (storeStatus == null) {
+            // No copies of the data
+            storeCopy = ClusterAllocationExplanation.StoreCopy.NONE;
+        } else {
+            final Throwable storeErr = storeStatus.getStoreException();
+            if (storeErr != null) {
+                if (ExceptionsHelper.unwrapCause(storeErr) instanceof CorruptIndexException) {
+                    storeCopy = ClusterAllocationExplanation.StoreCopy.CORRUPT;
+                } else {
+                    storeCopy = ClusterAllocationExplanation.StoreCopy.IO_ERROR;
+                }
+            } else if (activeAllocationIds.isEmpty()) {
+                // The ids are only empty if dealing with a legacy index
+                // TODO: fetch the shard state versions and display here?
+                storeCopy = ClusterAllocationExplanation.StoreCopy.UNKNOWN;
+            } else if (activeAllocationIds.contains(storeStatus.getAllocationId())) {
+                storeCopy = ClusterAllocationExplanation.StoreCopy.AVAILABLE;
+            } else {
+                // Otherwise, this is a stale copy of the data (allocation ids don't match)
+                storeCopy = ClusterAllocationExplanation.StoreCopy.STALE;
+            }
+        }
+
+        if (node.getId().equals(assignedNodeId)) {
+            finalDecision = ClusterAllocationExplanation.FinalDecision.ALREADY_ASSIGNED;
+            finalExplanation = "the shard is already assigned to this node";
+        } else if (shard.primary() && shard.unassigned() && shard.allocatedPostIndexCreate(indexMetaData) &&
+                storeCopy == ClusterAllocationExplanation.StoreCopy.STALE) {
+            finalExplanation = "the copy of the shard is stale, allocation ids do not match";
+            finalDecision = ClusterAllocationExplanation.FinalDecision.NO;
+        } else if (shard.primary() && shard.unassigned() && shard.allocatedPostIndexCreate(indexMetaData) &&
+                storeCopy == ClusterAllocationExplanation.StoreCopy.NONE) {
+            finalExplanation = "there is no copy of the shard available";
+            finalDecision = ClusterAllocationExplanation.FinalDecision.NO;
+        } else if (shard.primary() && shard.unassigned() && storeCopy == ClusterAllocationExplanation.StoreCopy.CORRUPT) {
+            finalExplanation = "the copy of the shard is corrupt";
+            finalDecision = ClusterAllocationExplanation.FinalDecision.NO;
+        } else if (shard.primary() && shard.unassigned() && storeCopy == ClusterAllocationExplanation.StoreCopy.IO_ERROR) {
+            finalExplanation = "the copy of the shard cannot be read";
+            finalDecision = ClusterAllocationExplanation.FinalDecision.NO;
+        } else {
+            if (nodeDecision.type() == Decision.Type.NO) {
+                finalDecision = ClusterAllocationExplanation.FinalDecision.NO;
+                finalExplanation = "the shard cannot be assigned because one or more allocation decider returns a 'NO' decision";
+            } else {
+                finalDecision = ClusterAllocationExplanation.FinalDecision.YES;
+                if (storeCopy == ClusterAllocationExplanation.StoreCopy.AVAILABLE) {
+                    finalExplanation = "the shard can be assigned and the node contains a valid copy of the shard data";
+                } else {
+                    finalExplanation = "the shard can be assigned";
+                }
+            }
+        }
+        return new NodeExplanation(node, nodeDecision, nodeWeight, storeStatus, finalDecision, finalExplanation, storeCopy);
+    }
+
+
     /**
      * For the given {@code ShardRouting}, return the explanation of the allocation for that shard on all nodes. If {@code
      * includeYesDecisions} is true, returns all decisions, otherwise returns only 'NO' and 'THROTTLE' decisions.
      */
     public static ClusterAllocationExplanation explainShard(ShardRouting shard, RoutingAllocation allocation, RoutingNodes routingNodes,
-                                                            boolean includeYesDecisions, ShardsAllocator shardAllocator) {
+                                                            boolean includeYesDecisions, ShardsAllocator shardAllocator,
+                                                            List<IndicesShardStoresResponse.StoreStatus> shardStores) {
         // don't short circuit deciders, we want a full explanation
         allocation.debugDecision(true);
         // get the existing unassigned info if available
@@ -139,14 +224,35 @@ public class TransportClusterAllocationExplainAction
                 nodeToDecision.put(discoNode, d);
             }
         }
-        long remainingDelayNanos = 0;
+        long remainingDelayMillis = 0;
+        final MetaData metadata = allocation.metaData();
+        final IndexMetaData indexMetaData = metadata.index(shard.index());
         if (ui != null) {
-            final MetaData metadata = allocation.metaData();
-            final Settings indexSettings = metadata.index(shard.index()).getSettings();
-            remainingDelayNanos = ui.getRemainingDelay(System.nanoTime(), metadata.settings(), indexSettings);
+            final Settings indexSettings = indexMetaData.getSettings();
+            long remainingDelayNanos = ui.getRemainingDelay(System.nanoTime(), metadata.settings(), indexSettings);
+            remainingDelayMillis = TimeValue.timeValueNanos(remainingDelayNanos).millis();
         }
-        return new ClusterAllocationExplanation(shard.shardId(), shard.primary(), shard.currentNodeId(), ui, nodeToDecision,
-                shardAllocator.weighShard(allocation, shard), remainingDelayNanos);
+
+        // Calculate weights for each of the nodes
+        Map<DiscoveryNode, Float> weights = shardAllocator.weighShard(allocation, shard);
+
+        Map<DiscoveryNode, IndicesShardStoresResponse.StoreStatus> nodeToStatus = new HashMap<>(shardStores.size());
+        for (IndicesShardStoresResponse.StoreStatus status : shardStores) {
+            nodeToStatus.put(status.getNode(), status);
+        }
+
+        Map<DiscoveryNode, NodeExplanation> explanations = new HashMap<>(shardStores.size());
+        for (Map.Entry<DiscoveryNode, Decision> entry : nodeToDecision.entrySet()) {
+            DiscoveryNode node = entry.getKey();
+            Decision decision = entry.getValue();
+            Float weight = weights.get(node);
+            IndicesShardStoresResponse.StoreStatus storeStatus = nodeToStatus.get(node);
+            NodeExplanation nodeExplanation = calculateNodeExplanation(shard, indexMetaData, node, decision, weight,
+                    storeStatus, shard.currentNodeId(), indexMetaData.activeAllocationIds(shard.getId()));
+            explanations.put(node, nodeExplanation);
+        }
+        return new ClusterAllocationExplanation(shard.shardId(), shard.primary(),
+                shard.currentNodeId(), remainingDelayMillis, ui, explanations);
     }
 
     @Override
@@ -156,30 +262,30 @@ public class TransportClusterAllocationExplainAction
         final RoutingAllocation allocation = new RoutingAllocation(allocationDeciders, routingNodes, state.nodes(),
                 clusterInfoService.getClusterInfo(), System.nanoTime());
 
-        ShardRouting shardRouting = null;
+        ShardRouting foundShard = null;
         if (request.useAnyUnassignedShard()) {
             // If we can use any shard, just pick the first unassigned one (if there are any)
             RoutingNodes.UnassignedShards.UnassignedIterator ui = routingNodes.unassigned().iterator();
             if (ui.hasNext()) {
-                shardRouting = ui.next();
+                foundShard = ui.next();
             }
         } else {
             String index = request.getIndex();
             int shard = request.getShard();
             if (request.isPrimary()) {
                 // If we're looking for the primary shard, there's only one copy, so pick it directly
-                shardRouting = allocation.routingTable().shardRoutingTable(index, shard).primaryShard();
+                foundShard = allocation.routingTable().shardRoutingTable(index, shard).primaryShard();
             } else {
                 // If looking for a replica, go through all the replica shards
                 List<ShardRouting> replicaShardRoutings = allocation.routingTable().shardRoutingTable(index, shard).replicaShards();
                 if (replicaShardRoutings.size() > 0) {
                     // Pick the first replica at the very least
-                    shardRouting = replicaShardRoutings.get(0);
+                    foundShard = replicaShardRoutings.get(0);
                     // In case there are multiple replicas where some are assigned and some aren't,
                     // try to find one that is unassigned at least
                     for (ShardRouting replica : replicaShardRoutings) {
                         if (replica.unassigned()) {
-                            shardRouting = replica;
+                            foundShard = replica;
                             break;
                         }
                     }
@@ -187,14 +293,34 @@ public class TransportClusterAllocationExplainAction
             }
         }
 
-        if (shardRouting == null) {
+        if (foundShard == null) {
             listener.onFailure(new ElasticsearchException("unable to find any shards to explain [{}] in the routing table", request));
             return;
         }
+        final ShardRouting shardRouting = foundShard;
         logger.debug("explaining the allocation for [{}], found shard [{}]", request, shardRouting);
 
-        ClusterAllocationExplanation cae = explainShard(shardRouting, allocation, routingNodes,
-                request.includeYesDecisions(), shardAllocator);
-        listener.onResponse(new ClusterAllocationExplainResponse(cae));
+        getShardStores(shardRouting, new ActionListener<IndicesShardStoresResponse>() {
+            @Override
+            public void onResponse(IndicesShardStoresResponse shardStoreResponse) {
+                ImmutableOpenIntMap<List<IndicesShardStoresResponse.StoreStatus>> shardStatuses =
+                        shardStoreResponse.getStoreStatuses().get(shardRouting.getIndexName());
+                List<IndicesShardStoresResponse.StoreStatus> shardStoreStatus = shardStatuses.get(shardRouting.id());
+                ClusterAllocationExplanation cae = explainShard(shardRouting, allocation, routingNodes,
+                        request.includeYesDecisions(), shardAllocator, shardStoreStatus);
+                listener.onResponse(new ClusterAllocationExplainResponse(cae));
+            }
+
+            @Override
+            public void onFailure(Throwable e) {
+                listener.onFailure(e);
+            }
+        });
+    }
+
+    private void getShardStores(ShardRouting shard, final ActionListener<IndicesShardStoresResponse> listener) {
+        IndicesShardStoresRequest request = new IndicesShardStoresRequest(shard.getIndexName());
+        request.shardStatuses("all");
+        shardStoresAction.execute(request, listener);
     }
 }

core/src/main/java/org/elasticsearch/action/admin/indices/shards/IndicesShardStoresResponse.java

@@ -164,7 +164,7 @@ public class IndicesShardStoresResponse extends ActionResponse implements ToXCon
             return allocationStatus;
         }
 
-        static StoreStatus readStoreStatus(StreamInput in) throws IOException {
+        public static StoreStatus readStoreStatus(StreamInput in) throws IOException {
             StoreStatus storeStatus = new StoreStatus();
             storeStatus.readFrom(in);
             return storeStatus;

core/src/test/java/org/elasticsearch/action/admin/cluster/allocation/ClusterAllocationExplainIT.java

@@ -20,14 +20,21 @@
 package org.elasticsearch.action.admin.cluster.allocation;
 
 import org.elasticsearch.action.admin.cluster.node.stats.NodesStatsResponse;
+import org.elasticsearch.action.admin.indices.shards.IndicesShardStoresResponse;
+import org.elasticsearch.client.Requests;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
+import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.routing.UnassignedInfo;
+import org.elasticsearch.cluster.routing.allocation.decider.Decision;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.test.ESIntegTestCase;
 import org.elasticsearch.test.ESSingleNodeTestCase;
 
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
+import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.greaterThan;
 import static org.hamcrest.Matchers.greaterThanOrEqualTo;
@@ -68,6 +75,101 @@ public final class ClusterAllocationExplainIT extends ESIntegTestCase {
         assertThat(cae.getShard().getIndexName(), equalTo("test"));
         assertFalse(cae.isPrimary());
         assertFalse(cae.isAssigned());
-        assertThat("expecting a remaining delay, got: " + cae.getRemainingDelayNanos(), cae.getRemainingDelayNanos(), greaterThan(0L));
+        assertThat("expecting a remaining delay, got: " + cae.getRemainingDelayMillis(), cae.getRemainingDelayMillis(), greaterThan(0L));
+    }
+
+    public void testUnassignedShards() throws Exception {
+        logger.info("--> starting 3 nodes");
+        String noAttrNode = internalCluster().startNode();
+        String barAttrNode = internalCluster().startNode(Settings.builder().put("node.attr.bar", "baz"));
+        String fooBarAttrNode = internalCluster().startNode(Settings.builder()
+                .put("node.attr.foo", "bar")
+                .put("node.attr.bar", "baz"));
+
+        // Wait for all 3 nodes to be up
+        logger.info("--> waiting for 3 nodes to be up");
+        client().admin().cluster().health(Requests.clusterHealthRequest().waitForNodes("3")).actionGet();
+
+        client().admin().indices().prepareCreate("anywhere")
+                .setSettings(Settings.builder()
+                        .put("index.number_of_shards", 5)
+                        .put("index.number_of_replicas", 1))
+                .get();
+
+        client().admin().indices().prepareCreate("only-baz")
+                .setSettings(Settings.builder()
+                        .put("index.routing.allocation.include.bar", "baz")
+                        .put("index.number_of_shards", 5)
+                        .put("index.number_of_replicas", 1))
+                .get();
+
+        client().admin().indices().prepareCreate("only-foo")
+                .setSettings(Settings.builder()
+                        .put("index.routing.allocation.include.foo", "bar")
+                        .put("index.number_of_shards", 1)
+                        .put("index.number_of_replicas", 1))
+                .get();
+
+        ensureGreen("anywhere", "only-baz");
+        ensureYellow("only-foo");
+
+        ClusterAllocationExplainResponse resp = client().admin().cluster().prepareAllocationExplain()
+                .setIndex("only-foo")
+                .setShard(0)
+                .setPrimary(false)
+                .get();
+        ClusterAllocationExplanation cae = resp.getExplanation();
+        assertThat(cae.getShard().getIndexName(), equalTo("only-foo"));
+        assertFalse(cae.isPrimary());
+        assertFalse(cae.isAssigned());
+        assertThat(UnassignedInfo.Reason.INDEX_CREATED, equalTo(cae.getUnassignedInfo().getReason()));
+        assertThat("expecting no remaining delay: " + cae.getRemainingDelayMillis(), cae.getRemainingDelayMillis(), equalTo(0L));
+
+        Map<DiscoveryNode, NodeExplanation> explanations = cae.getNodeExplanations();
+
+        Float noAttrWeight = -1f;
+        Float barAttrWeight = -1f;
+        Float fooBarAttrWeight = -1f;
+        for (Map.Entry<DiscoveryNode, NodeExplanation> entry : explanations.entrySet()) {
+            DiscoveryNode node = entry.getKey();
+            String nodeName = node.getName();
+            NodeExplanation explanation = entry.getValue();
+            ClusterAllocationExplanation.FinalDecision finalDecision = explanation.getFinalDecision();
+            String finalExplanation = explanation.getFinalExplanation();
+            ClusterAllocationExplanation.StoreCopy storeCopy = explanation.getStoreCopy();
+            Decision d = explanation.getDecision();
+            float weight = explanation.getWeight();
+            IndicesShardStoresResponse.StoreStatus storeStatus = explanation.getStoreStatus();
+
+            assertEquals(d.type(), Decision.Type.NO);
+            if (noAttrNode.equals(nodeName)) {
+                assertThat(d.toString(), containsString("node does not match index include filters [foo:\"bar\"]"));
+                noAttrWeight = weight;
+                assertNull(storeStatus);
+                assertEquals("the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
+                        explanation.getFinalExplanation());
+                assertEquals(ClusterAllocationExplanation.FinalDecision.NO, finalDecision);
+            } else if (barAttrNode.equals(nodeName)) {
+                assertThat(d.toString(), containsString("node does not match index include filters [foo:\"bar\"]"));
+                barAttrWeight = weight;
+                assertNull(storeStatus);
+                assertEquals("the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
+                        explanation.getFinalExplanation());
+                assertEquals(ClusterAllocationExplanation.FinalDecision.NO, finalDecision);
+            } else if (fooBarAttrNode.equals(nodeName)) {
+                assertThat(d.toString(), containsString("the shard cannot be allocated on the same node id"));
+                fooBarAttrWeight = weight;
+                assertEquals(storeStatus.getAllocationStatus(),
+                        IndicesShardStoresResponse.StoreStatus.AllocationStatus.PRIMARY);
+                assertEquals(ClusterAllocationExplanation.FinalDecision.NO, finalDecision);
+                assertEquals(ClusterAllocationExplanation.StoreCopy.AVAILABLE, storeCopy);
+                assertEquals("the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
+                        explanation.getFinalExplanation());
+            } else {
+                fail("unexpected node with name: " + nodeName +
+                     ", I have: " + noAttrNode + ", " + barAttrNode + ", " + fooBarAttrNode);
+            }
+        }
+        assertFalse(barAttrWeight == fooBarAttrWeight);
     }
 }

core/src/test/java/org/elasticsearch/action/admin/cluster/allocation/ClusterAllocationExplainTests.java

@@ -43,16 +43,22 @@ public final class ClusterAllocationExplainTests extends ESSingleNodeTestCase {
         assertEquals(false, cae.isPrimary());
         assertNull(cae.getAssignedNodeId());
         assertNotNull(cae.getUnassignedInfo());
-        Decision d = cae.getNodeDecisions().values().iterator().next();
+        NodeExplanation explanation = cae.getNodeExplanations().values().iterator().next();
+        ClusterAllocationExplanation.FinalDecision fd = explanation.getFinalDecision();
+        ClusterAllocationExplanation.StoreCopy storeCopy = explanation.getStoreCopy();
+        String finalExplanation = explanation.getFinalExplanation();
+        Decision d = explanation.getDecision();
         assertNotNull("should have a decision", d);
         assertEquals(Decision.Type.NO, d.type());
+        assertEquals(ClusterAllocationExplanation.FinalDecision.NO, fd);
+        assertEquals(ClusterAllocationExplanation.StoreCopy.AVAILABLE, storeCopy);
         assertTrue(d.toString(), d.toString().contains("NO(the shard cannot be allocated on the same node id"));
         assertTrue(d instanceof Decision.Multi);
         Decision.Multi md = (Decision.Multi) d;
         Decision ssd = md.getDecisions().get(0);
         assertEquals(Decision.Type.NO, ssd.type());
         assertTrue(ssd.toString(), ssd.toString().contains("NO(the shard cannot be allocated on the same node id"));
-        Float weight = cae.getNodeWeights().values().iterator().next();
+        Float weight = explanation.getWeight();
         assertNotNull("should have a weight", weight);
 
         resp = client().admin().cluster().prepareAllocationExplain().setIndex("test").setShard(0).setPrimary(true).get();
@@ -64,16 +70,22 @@ public final class ClusterAllocationExplainTests extends ESSingleNodeTestCase {
         assertEquals(true, cae.isPrimary());
         assertNotNull("shard should have assigned node id", cae.getAssignedNodeId());
         assertNull("assigned shard should not have unassigned info", cae.getUnassignedInfo());
-        d = cae.getNodeDecisions().values().iterator().next();
+        explanation = cae.getNodeExplanations().values().iterator().next();
+        d = explanation.getDecision();
+        fd = explanation.getFinalDecision();
+        storeCopy = explanation.getStoreCopy();
+        finalExplanation = explanation.getFinalExplanation();
         assertNotNull("should have a decision", d);
         assertEquals(Decision.Type.NO, d.type());
+        assertEquals(ClusterAllocationExplanation.FinalDecision.ALREADY_ASSIGNED, fd);
+        assertEquals(ClusterAllocationExplanation.StoreCopy.AVAILABLE, storeCopy);
         assertTrue(d.toString(), d.toString().contains("NO(the shard cannot be allocated on the same node id"));
         assertTrue(d instanceof Decision.Multi);
         md = (Decision.Multi) d;
         ssd = md.getDecisions().get(0);
         assertEquals(Decision.Type.NO, ssd.type());
         assertTrue(ssd.toString(), ssd.toString().contains("NO(the shard cannot be allocated on the same node id"));
-        weight = cae.getNodeWeights().values().iterator().next();
+        weight = explanation.getWeight();
         assertNotNull("should have a weight", weight);
 
         resp = client().admin().cluster().prepareAllocationExplain().useAnyUnassignedShard().get();

core/src/test/java/org/elasticsearch/action/admin/cluster/allocation/ClusterAllocationExplanationTests.java

@@ -19,17 +19,36 @@
 
 package org.elasticsearch.action.admin.cluster.allocation;
 
+import org.apache.lucene.index.CorruptIndexException;
+import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.ExceptionsHelper;
 import org.elasticsearch.Version;
+import org.elasticsearch.action.admin.indices.shards.IndicesShardStoresResponse;
+import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.cluster.routing.ShardRouting;
+import org.elasticsearch.cluster.routing.ShardRoutingHelper;
+import org.elasticsearch.cluster.routing.UnassignedInfo;
 import org.elasticsearch.cluster.routing.allocation.decider.Decision;
 import org.elasticsearch.common.io.stream.BytesStreamOutput;
 import org.elasticsearch.common.io.stream.StreamInput;
+import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.transport.DummyTransportAddress;
+import org.elasticsearch.common.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.common.xcontent.XContentFactory;
+import org.elasticsearch.index.Index;
 import org.elasticsearch.index.shard.ShardId;
 import org.elasticsearch.test.ESTestCase;
 
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
 import java.util.Map;
+import java.util.Set;
 
 import static java.util.Collections.emptyMap;
 import static java.util.Collections.emptySet;
@@ -39,6 +58,131 @@ import static java.util.Collections.emptySet;
  */
 public final class ClusterAllocationExplanationTests extends ESTestCase {
 
+    private Index i = new Index("foo", "uuid");
+    private ShardRouting primaryShard = ShardRouting.newUnassigned(i, 0, null, true,
+            new UnassignedInfo(UnassignedInfo.Reason.INDEX_CREATED, "foo"));
+    private ShardRouting replicaShard = ShardRouting.newUnassigned(i, 0, null, false,
+            new UnassignedInfo(UnassignedInfo.Reason.INDEX_CREATED, "foo"));
+    private IndexMetaData indexMetaData = IndexMetaData.builder("foo")
+            .settings(Settings.builder()
+                    .put(IndexMetaData.SETTING_VERSION_CREATED, Version.CURRENT)
+                    .put(IndexMetaData.SETTING_INDEX_UUID, "uuid"))
+            .putActiveAllocationIds(0, new HashSet<String>(Arrays.asList("aid1", "aid2")))
+            .numberOfShards(1)
+            .numberOfReplicas(1)
+            .build();
+    private DiscoveryNode node = new DiscoveryNode("node-0", DummyTransportAddress.INSTANCE, emptyMap(), emptySet(), Version.CURRENT);
+    private static Decision.Multi yesDecision = new Decision.Multi();
+    private static Decision.Multi noDecision = new Decision.Multi();
+
+    static {
+        yesDecision.add(Decision.single(Decision.Type.YES, "yes label", "yes please"));
+        noDecision.add(Decision.single(Decision.Type.NO, "no label", "no thanks"));
+    }
+
+
+    private NodeExplanation makeNodeExplanation(boolean primary, boolean isAssigned, boolean hasErr, boolean hasActiveId) {
+        Float nodeWeight = randomFloat();
+        Exception e = hasErr ? new ElasticsearchException("stuff's broke, yo") : null;
+        IndicesShardStoresResponse.StoreStatus storeStatus = new IndicesShardStoresResponse.StoreStatus(node, 42, "eggplant",
+                IndicesShardStoresResponse.StoreStatus.AllocationStatus.PRIMARY, e);
+        String assignedNodeId;
+        if (isAssigned) {
+            assignedNodeId = "node-0";
+        } else {
+            assignedNodeId = "node-9";
+        }
+        Set<String> activeAllocationIds = new HashSet<>();
+        if (hasActiveId) {
+            activeAllocationIds.add("eggplant");
+        }
+
+        return TransportClusterAllocationExplainAction.calculateNodeExplanation(primary ? primaryShard : replicaShard,
+                indexMetaData, node, noDecision, nodeWeight, storeStatus, assignedNodeId, activeAllocationIds);
+    }
+
+    private void assertExplanations(NodeExplanation ne, String finalExplanation, ClusterAllocationExplanation.FinalDecision finalDecision,
+                                    ClusterAllocationExplanation.StoreCopy storeCopy) {
+        assertEquals(finalExplanation, ne.getFinalExplanation());
+        assertEquals(finalDecision, ne.getFinalDecision());
+        assertEquals(storeCopy, ne.getStoreCopy());
+    }
+
+    public void testDecisionAndExplanation() {
+        Exception e = new IOException("stuff's broke, yo");
+        Exception corruptE = new CorruptIndexException("stuff's corrupt, yo", "");
+        Float nodeWeight = randomFloat();
+        Set<String> activeAllocationIds = new HashSet<>();
+        activeAllocationIds.add("eggplant");
+        ShardRouting primaryStartedShard = ShardRouting.newUnassigned(i, 0, null, true,
+                new UnassignedInfo(UnassignedInfo.Reason.INDEX_REOPENED, "foo"));
+        assertTrue(primaryStartedShard.allocatedPostIndexCreate(indexMetaData));
+
+        IndicesShardStoresResponse.StoreStatus storeStatus = new IndicesShardStoresResponse.StoreStatus(node, 42, "eggplant",
+                IndicesShardStoresResponse.StoreStatus.AllocationStatus.PRIMARY, e);
+        NodeExplanation ne = TransportClusterAllocationExplainAction.calculateNodeExplanation(primaryShard, indexMetaData, node,
+                yesDecision, nodeWeight, storeStatus, "", activeAllocationIds);
+        assertExplanations(ne, "the copy of the shard cannot be read",
+                ClusterAllocationExplanation.FinalDecision.NO, ClusterAllocationExplanation.StoreCopy.IO_ERROR);
+
+        ne = TransportClusterAllocationExplainAction.calculateNodeExplanation(primaryShard, indexMetaData, node, yesDecision, nodeWeight,
+                null, "", activeAllocationIds);
+        assertExplanations(ne, "the shard can be assigned",
+                ClusterAllocationExplanation.FinalDecision.YES, ClusterAllocationExplanation.StoreCopy.NONE);
+
+        ne = TransportClusterAllocationExplainAction.calculateNodeExplanation(primaryStartedShard, indexMetaData, node, yesDecision,
+                nodeWeight, null, "", activeAllocationIds);
+        assertExplanations(ne, "there is no copy of the shard available",
+                ClusterAllocationExplanation.FinalDecision.NO, ClusterAllocationExplanation.StoreCopy.NONE);
+
+        ne = TransportClusterAllocationExplainAction.calculateNodeExplanation(primaryShard, indexMetaData, node, noDecision, nodeWeight,
+                null, "", activeAllocationIds);
+        assertExplanations(ne, "the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
+                ClusterAllocationExplanation.FinalDecision.NO, ClusterAllocationExplanation.StoreCopy.NONE);
+
+        storeStatus = new IndicesShardStoresResponse.StoreStatus(node, 42, "eggplant",
+                IndicesShardStoresResponse.StoreStatus.AllocationStatus.PRIMARY, null);
+        ne = TransportClusterAllocationExplainAction.calculateNodeExplanation(primaryShard, indexMetaData, node, noDecision, nodeWeight,
+                storeStatus, "", activeAllocationIds);
+        assertExplanations(ne, "the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
+                ClusterAllocationExplanation.FinalDecision.NO, ClusterAllocationExplanation.StoreCopy.AVAILABLE);
+
+        storeStatus = new IndicesShardStoresResponse.StoreStatus(node, 42, "eggplant",
+                IndicesShardStoresResponse.StoreStatus.AllocationStatus.PRIMARY, corruptE);
+        ne = TransportClusterAllocationExplainAction.calculateNodeExplanation(primaryShard, indexMetaData, node, yesDecision, nodeWeight,
+                storeStatus, "", activeAllocationIds);
+        assertExplanations(ne, "the copy of the shard is corrupt",
+                ClusterAllocationExplanation.FinalDecision.NO, ClusterAllocationExplanation.StoreCopy.CORRUPT);
+
+        storeStatus = new IndicesShardStoresResponse.StoreStatus(node, 42, "banana",
+                IndicesShardStoresResponse.StoreStatus.AllocationStatus.PRIMARY, null);
+        ne = TransportClusterAllocationExplainAction.calculateNodeExplanation(primaryShard, indexMetaData, node, yesDecision, nodeWeight,
+                storeStatus, "", activeAllocationIds);
+        assertExplanations(ne, "the shard can be assigned",
+                ClusterAllocationExplanation.FinalDecision.YES, ClusterAllocationExplanation.StoreCopy.STALE);
+
+        storeStatus = new IndicesShardStoresResponse.StoreStatus(node, 42, "banana",
+                IndicesShardStoresResponse.StoreStatus.AllocationStatus.PRIMARY, null);
+        ne = TransportClusterAllocationExplainAction.calculateNodeExplanation(primaryStartedShard, indexMetaData, node, yesDecision,
+                nodeWeight, storeStatus, "", activeAllocationIds);
+        assertExplanations(ne, "the copy of the shard is stale, allocation ids do not match",
+                ClusterAllocationExplanation.FinalDecision.NO, ClusterAllocationExplanation.StoreCopy.STALE);
+
+        storeStatus = new IndicesShardStoresResponse.StoreStatus(node, 42, "eggplant",
+                IndicesShardStoresResponse.StoreStatus.AllocationStatus.PRIMARY, null);
+        ne = TransportClusterAllocationExplainAction.calculateNodeExplanation(primaryShard, indexMetaData, node, yesDecision, nodeWeight,
+                storeStatus, "node-0", activeAllocationIds);
+        assertExplanations(ne, "the shard is already assigned to this node",
+                ClusterAllocationExplanation.FinalDecision.ALREADY_ASSIGNED, ClusterAllocationExplanation.StoreCopy.AVAILABLE);
+
+        storeStatus = new IndicesShardStoresResponse.StoreStatus(node, 42, "eggplant",
+                IndicesShardStoresResponse.StoreStatus.AllocationStatus.PRIMARY, null);
+        ne = TransportClusterAllocationExplainAction.calculateNodeExplanation(primaryShard, indexMetaData, node, yesDecision, nodeWeight,
+                storeStatus, "", activeAllocationIds);
+        assertExplanations(ne, "the shard can be assigned and the node contains a valid copy of the shard data",
+                ClusterAllocationExplanation.FinalDecision.YES, ClusterAllocationExplanation.StoreCopy.AVAILABLE);
+}
+
     public void testDecisionEquality() {
         Decision.Multi d = new Decision.Multi();
         Decision.Multi d2 = new Decision.Multi();
@@ -53,21 +197,19 @@ public final class ClusterAllocationExplanationTests extends ESTestCase {
 
     public void testExplanationSerialization() throws Exception {
         ShardId shard = new ShardId("test", "uuid", 0);
-        Map<DiscoveryNode, Decision> nodeToDecisions = new HashMap<>();
-        Map<DiscoveryNode, Float> nodeToWeight = new HashMap<>();
-        for (int i = randomIntBetween(2, 5); i > 0; i--) {
-            DiscoveryNode dn = new DiscoveryNode("node-" + i, DummyTransportAddress.INSTANCE, emptyMap(), emptySet(), Version.CURRENT);
-            Decision.Multi d = new Decision.Multi();
-            d.add(Decision.single(Decision.Type.NO, "no label", "because I said no"));
-            d.add(Decision.single(Decision.Type.YES, "yes label", "yes please"));
-            d.add(Decision.single(Decision.Type.THROTTLE, "throttle label", "wait a sec"));
-            nodeToDecisions.put(dn, d);
-            nodeToWeight.put(dn, randomFloat());
-        }
-
         long remainingDelay = randomIntBetween(0, 500);
-        ClusterAllocationExplanation cae = new ClusterAllocationExplanation(shard, true, "assignedNode", null,
-                nodeToDecisions, nodeToWeight, remainingDelay);
+        Map<DiscoveryNode, NodeExplanation> nodeExplanations = new HashMap<>(1);
+        Float nodeWeight = randomFloat();
+        Set<String> activeAllocationIds = new HashSet<>();
+        activeAllocationIds.add("eggplant");
+
+        IndicesShardStoresResponse.StoreStatus storeStatus = new IndicesShardStoresResponse.StoreStatus(node, 42, "eggplant",
+                IndicesShardStoresResponse.StoreStatus.AllocationStatus.PRIMARY, null);
+        NodeExplanation ne = TransportClusterAllocationExplainAction.calculateNodeExplanation(primaryShard, indexMetaData, node,
+                yesDecision, nodeWeight, storeStatus, "", activeAllocationIds);
+        nodeExplanations.put(ne.getNode(), ne);
+        ClusterAllocationExplanation cae = new ClusterAllocationExplanation(shard, true,
+                "assignedNode", remainingDelay, null, nodeExplanations);
         BytesStreamOutput out = new BytesStreamOutput();
         cae.writeTo(out);
         StreamInput in = StreamInput.wrap(out.bytes());
@@ -77,10 +219,45 @@ public final class ClusterAllocationExplanationTests extends ESTestCase {
         assertTrue(cae2.isAssigned());
         assertEquals("assignedNode", cae2.getAssignedNodeId());
         assertNull(cae2.getUnassignedInfo());
-        for (Map.Entry<DiscoveryNode, Decision> entry : cae2.getNodeDecisions().entrySet()) {
-            assertEquals(nodeToDecisions.get(entry.getKey()), entry.getValue());
+        assertEquals(remainingDelay, cae2.getRemainingDelayMillis());
+        for (Map.Entry<DiscoveryNode, NodeExplanation> entry : cae2.getNodeExplanations().entrySet()) {
+            DiscoveryNode node = entry.getKey();
+            NodeExplanation explanation = entry.getValue();
+            IndicesShardStoresResponse.StoreStatus status = explanation.getStoreStatus();
+            assertNotNull(explanation.getStoreStatus());
+            assertNotNull(explanation.getDecision());
+            assertEquals(nodeWeight, explanation.getWeight());
         }
-        assertEquals(nodeToWeight, cae2.getNodeWeights());
-        assertEquals(remainingDelay, cae2.getRemainingDelayNanos());
+    }
+
+    public void testExplanationToXContent() throws Exception {
+        ShardId shardId = new ShardId("foo", "uuid", 0);
+        long remainingDelay = 42;
+        Decision.Multi d = new Decision.Multi();
+        d.add(Decision.single(Decision.Type.NO, "no label", "because I said no"));
+        d.add(Decision.single(Decision.Type.YES, "yes label", "yes please"));
+        d.add(Decision.single(Decision.Type.THROTTLE, "throttle label", "wait a sec"));
+        Float nodeWeight = 1.5f;
+        Set<String> allocationIds = new HashSet<>();
+        allocationIds.add("bar");
+        IndicesShardStoresResponse.StoreStatus storeStatus = new IndicesShardStoresResponse.StoreStatus(node, 42, "eggplant",
+                IndicesShardStoresResponse.StoreStatus.AllocationStatus.PRIMARY, new ElasticsearchException("stuff's broke, yo"));
+        NodeExplanation ne = TransportClusterAllocationExplainAction.calculateNodeExplanation(primaryShard, indexMetaData, node,
+                d, nodeWeight, storeStatus, "node-0", allocationIds);
+        Map<DiscoveryNode, NodeExplanation> nodeExplanations = new HashMap<>(1);
+        nodeExplanations.put(ne.getNode(), ne);
+        ClusterAllocationExplanation cae = new ClusterAllocationExplanation(shardId, true,
+                "assignedNode", remainingDelay, null, nodeExplanations);
+        XContentBuilder builder = XContentFactory.jsonBuilder();
+        cae.toXContent(builder, ToXContent.EMPTY_PARAMS);
+        assertEquals("{\"shard\":{\"index\":\"foo\",\"index_uuid\":\"uuid\",\"id\":0,\"primary\":true},\"assigned\":true," +
+                        "\"assigned_node_id\":\"assignedNode\",\"nodes\":{\"node-0\":{\"node_name\":\"\",\"node_attribute" +
+                        "s\":{},\"store\":{\"shard_copy\":\"IO_ERROR\",\"store_exception\":\"ElasticsearchException[stuff" +
+                        "'s broke, yo]\"},\"final_decision\":\"ALREADY_ASSIGNED\",\"final_explanation\":\"the shard is al" +
+                        "ready assigned to this node\",\"weight\":1.5,\"decisions\":[{\"decider\":\"no label\",\"decision" +
+                        "\":\"NO\",\"explanation\":\"because I said no\"},{\"decider\":\"yes label\",\"decision\":\"YES\"" +
+                        ",\"explanation\":\"yes please\"},{\"decider\":\"throttle label\",\"decision\":\"THROTTLE\",\"exp" +
+                        "lanation\":\"wait a sec\"}]}}}",
+                builder.string());
     }
 }