Only apply initial recovery filter to shrunk shard (#44054)

Today the `index.routing.allocation.initial_recovery._id` setting can only be
set on indices that are the result of a shrink, but the filtered allocation
decider also applies this filter to shards with a recovery source of
`EMPTY_STORE`. The only way to have this setting set while the recovery source
is `EMPTY_STORE` is to force-allocate an empty primary, but such a forced
allocation ignores this allocation decider.

This commit simplifies the allocation decider so that the `initial_recovery`
setting only applies to shards with a recovery source of `LOCAL_SHARDS`.

Author: DaveCTurner

server/src/main/java/org/elasticsearch/cluster/routing/allocation/decider/FilterAllocationDecider.java

@@ -30,7 +30,6 @@
 import org.elasticsearch.common.settings.Setting.Property;
 import org.elasticsearch.common.settings.Settings;
 
-import java.util.EnumSet;
 import java.util.Map;
 
 import static org.elasticsearch.cluster.node.DiscoveryNodeFilters.IP_VALIDATOR;
@@ -81,17 +80,6 @@ public class FilterAllocationDecider extends AllocationDecider {
         Setting.prefixKeySetting(CLUSTER_ROUTING_EXCLUDE_GROUP_PREFIX + ".", key ->
             Setting.simpleString(key, value -> IP_VALIDATOR.accept(key, value), Property.Dynamic, Property.NodeScope));
 
-    /**
-     * The set of {@link RecoverySource.Type} values for which the
-     * {@link IndexMetaData#INDEX_ROUTING_INITIAL_RECOVERY_GROUP_SETTING} should apply.
-     * Note that we do not include the {@link RecoverySource.Type#SNAPSHOT} type here
-     * because if the snapshot is restored to a different cluster that does not contain
-     * the initial recovery node id, or to the same cluster where the initial recovery node
-     * id has been decommissioned, then the primary shards will never be allocated.
-     */
-    static EnumSet<RecoverySource.Type> INITIAL_RECOVERY_TYPES =
-        EnumSet.of(RecoverySource.Type.EMPTY_STORE, RecoverySource.Type.LOCAL_SHARDS);
-
     private volatile DiscoveryNodeFilters clusterRequireFilters;
     private volatile DiscoveryNodeFilters clusterIncludeFilters;
     private volatile DiscoveryNodeFilters clusterExcludeFilters;
@@ -108,17 +96,16 @@ public FilterAllocationDecider(Settings settings, ClusterSettings clusterSetting
     @Override
     public Decision canAllocate(ShardRouting shardRouting, RoutingNode node, RoutingAllocation allocation) {
         if (shardRouting.unassigned()) {
-            // only for unassigned - we filter allocation right after the index creation ie. for shard shrinking etc. to ensure
+            // only for unassigned - we filter allocation right after the index creation (for shard shrinking) to ensure
             // that once it has been allocated post API the replicas can be allocated elsewhere without user interaction
             // this is a setting that can only be set within the system!
             IndexMetaData indexMd = allocation.metaData().getIndexSafe(shardRouting.index());
             DiscoveryNodeFilters initialRecoveryFilters = indexMd.getInitialRecoveryFilters();
             if (initialRecoveryFilters != null  &&
-                INITIAL_RECOVERY_TYPES.contains(shardRouting.recoverySource().getType()) &&
+                shardRouting.recoverySource().getType() == RecoverySource.Type.LOCAL_SHARDS &&
                 initialRecoveryFilters.match(node.node()) == false) {
-                String explanation = (shardRouting.recoverySource().getType() == RecoverySource.Type.LOCAL_SHARDS) ?
-                    "initial allocation of the shrunken index is only allowed on nodes [%s] that hold a copy of every shard in the index" :
-                    "initial allocation of the index is only allowed on nodes [%s]";
+                String explanation =
+                    "initial allocation of the shrunken index is only allowed on nodes [%s] that hold a copy of every shard in the index";
                 return allocation.decision(Decision.NO, NAME, explanation, initialRecoveryFilters);
             }
         }

server/src/test/java/org/elasticsearch/cluster/routing/allocation/decider/FilterAllocationDeciderTests.java

@@ -139,39 +139,25 @@ public void testFilterInitialRecovery() {
     }
 
     private ClusterState createInitialClusterState(AllocationService service, Settings settings) {
-        RecoverySource.Type recoveryType = randomFrom(FilterAllocationDecider.INITIAL_RECOVERY_TYPES);
         MetaData.Builder metaData = MetaData.builder();
         final Settings.Builder indexSettings = settings(Version.CURRENT).put(settings);
         final IndexMetaData sourceIndex;
-        if (recoveryType == RecoverySource.Type.LOCAL_SHARDS) {
-            //put a fake closed source index
-            sourceIndex = IndexMetaData.builder("sourceIndex")
-                .settings(settings(Version.CURRENT)).numberOfShards(2).numberOfReplicas(0)
-                .putInSyncAllocationIds(0, Collections.singleton("aid0"))
-                .putInSyncAllocationIds(1, Collections.singleton("aid1"))
-                .build();
-            metaData.put(sourceIndex, false);
-            indexSettings.put(INDEX_RESIZE_SOURCE_UUID.getKey(), sourceIndex.getIndexUUID());
-            indexSettings.put(INDEX_RESIZE_SOURCE_NAME.getKey(), sourceIndex.getIndex().getName());
-        } else {
-            sourceIndex = null;
-        }
+        //put a fake closed source index
+        sourceIndex = IndexMetaData.builder("sourceIndex")
+            .settings(settings(Version.CURRENT)).numberOfShards(2).numberOfReplicas(0)
+            .putInSyncAllocationIds(0, Collections.singleton("aid0"))
+            .putInSyncAllocationIds(1, Collections.singleton("aid1"))
+            .build();
+        metaData.put(sourceIndex, false);
+        indexSettings.put(INDEX_RESIZE_SOURCE_UUID.getKey(), sourceIndex.getIndexUUID());
+        indexSettings.put(INDEX_RESIZE_SOURCE_NAME.getKey(), sourceIndex.getIndex().getName());
         final IndexMetaData.Builder indexMetaDataBuilder = IndexMetaData.builder("idx").settings(indexSettings)
             .numberOfShards(1).numberOfReplicas(1);
         final IndexMetaData indexMetaData = indexMetaDataBuilder.build();
         metaData.put(indexMetaData, false);
         RoutingTable.Builder routingTableBuilder = RoutingTable.builder();
-        switch (recoveryType) {
-            case EMPTY_STORE:
-                routingTableBuilder.addAsNew(indexMetaData);
-                break;
-            case LOCAL_SHARDS:
-                routingTableBuilder.addAsFromCloseToOpen(sourceIndex);
-                routingTableBuilder.addAsNew(indexMetaData);
-                break;
-            default:
-                throw new UnsupportedOperationException(recoveryType + " is not supported");
-        }
+        routingTableBuilder.addAsFromCloseToOpen(sourceIndex);
+        routingTableBuilder.addAsNew(indexMetaData);
 
         RoutingTable routingTable = routingTableBuilder.build();
         ClusterState clusterState = ClusterState.builder(org.elasticsearch.cluster.ClusterName.CLUSTER_NAME_SETTING