Introduce ShardRouting.Role (#92668)

Introduces the concept of a `ShardRouting.Role` which allows plugins to
assign different roles to each shard copy in a replication group. Unlike
the primary/replica flag, a shard copy role sticks to the shard copy
throughout its life and is preserved across relocations and
reassignments.

Author: DaveCTurner

benchmarks/src/main/java/org/elasticsearch/benchmark/routing/allocation/AllocationBenchmark.java

@@ -131,7 +131,7 @@ public void setUp() throws Exception {
             );
         }
         Metadata metadata = mb.build();
-        RoutingTable.Builder rb = RoutingTable.builder();
+        RoutingTable.Builder rb = RoutingTable.builder(TestShardRoutingRoleStrategies.DEFAULT_ROLE_ONLY);
         for (int i = 1; i <= numIndices; i++) {
             rb.addAsNew(metadata.index("test_" + i));
         }

benchmarks/src/main/java/org/elasticsearch/benchmark/routing/allocation/Allocators.java

@@ -81,7 +81,8 @@ public static AllocationService createAllocationService(Settings settings, Clust
             NoopGatewayAllocator.INSTANCE,
             new BalancedShardsAllocator(settings),
             EmptyClusterInfoService.INSTANCE,
-            EmptySnapshotsInfoService.INSTANCE
+            EmptySnapshotsInfoService.INSTANCE,
+            TestShardRoutingRoleStrategies.DEFAULT_ROLE_ONLY
         );
     }
 

benchmarks/src/main/java/org/elasticsearch/benchmark/routing/allocation/ShardsAvailabilityHealthIndicatorBenchmark.java

@@ -129,15 +129,16 @@ public void setUp() throws Exception {
                 .numberOfReplicas(numReplicas)
                 .build();
 
-            final IndexRoutingTable.Builder indexRountingTableBuilder = new IndexRoutingTable.Builder(indexMetadata.getIndex());
+            final IndexRoutingTable.Builder indexRountingTableBuilder = IndexRoutingTable.builder(indexMetadata.getIndex());
             for (int shardIdNumber = 0; shardIdNumber < numShards; shardIdNumber++) {
                 ShardId shardId = new ShardId(indexMetadata.getIndex(), shardIdNumber);
                 final IndexShardRoutingTable.Builder shardBuilder = new IndexShardRoutingTable.Builder(shardId);
                 ShardRouting shardRouting = ShardRouting.newUnassigned(
                     shardId,
                     true,
                     RecoverySource.ExistingStoreRecoverySource.INSTANCE,
-                    decidersNoUnassignedInfo
+                    decidersNoUnassignedInfo,
+                    ShardRouting.Role.DEFAULT
                 );
                 shardBuilder.addShard(shardRouting);
                 if (shardIdNumber < numReplicas) {
@@ -146,7 +147,8 @@ public void setUp() throws Exception {
                             shardId,
                             false,
                             RecoverySource.EmptyStoreRecoverySource.INSTANCE,
-                            decidersNoUnassignedInfo
+                            decidersNoUnassignedInfo,
+                            ShardRouting.Role.DEFAULT
                         )
                     );
                 }

benchmarks/src/main/java/org/elasticsearch/benchmark/routing/allocation/TestShardRoutingRoleStrategies.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package org.elasticsearch.benchmark.routing.allocation;
+
+import org.elasticsearch.cluster.routing.ShardRouting;
+import org.elasticsearch.cluster.routing.ShardRoutingRoleStrategy;
+
+public class TestShardRoutingRoleStrategies {
+
+    /**
+     * A strategy which only returns the default role in all situations. This is deliberately not available to production code to avoid any
+     * possibility of using it instead of the strategy provided by the plugin (if so configured).
+     */
+    public static final ShardRoutingRoleStrategy DEFAULT_ROLE_ONLY = new ShardRoutingRoleStrategy() {
+        @Override
+        public ShardRouting.Role newReplicaRole() {
+            return ShardRouting.Role.DEFAULT;
+        }
+
+        @Override
+        public ShardRouting.Role newEmptyRole(int copyIndex) {
+            return ShardRouting.Role.DEFAULT;
+        }
+    };
+
+    private TestShardRoutingRoleStrategies() {
+        // no instances
+    }
+}

docs/changelog/92668.yaml

@@ -0,0 +1,5 @@
+pr: 92668
+summary: "Introduce ShardRouting.Role"
+area: Allocation
+type: enhancement
+issues: []

modules/data-streams/src/test/java/org/elasticsearch/datastreams/DataStreamGetWriteIndexTests.java

@@ -17,6 +17,7 @@
 import org.elasticsearch.action.admin.indices.rollover.MetadataRolloverService;
 import org.elasticsearch.action.index.IndexRequest;
 import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.TestShardRoutingRoleStrategies;
 import org.elasticsearch.cluster.metadata.ComposableIndexTemplate;
 import org.elasticsearch.cluster.metadata.DataStream;
 import org.elasticsearch.cluster.metadata.DataStreamTestHelper;
@@ -248,6 +249,7 @@ public void setup() throws Exception {
             when(env.sharedDataFile()).thenReturn(null);
             AllocationService allocationService = mock(AllocationService.class);
             when(allocationService.reroute(any(ClusterState.class), any(String.class), any())).then(i -> i.getArguments()[0]);
+            when(allocationService.getShardRoutingRoleStrategy()).thenReturn(TestShardRoutingRoleStrategies.DEFAULT_ROLE_ONLY);
             ShardLimitValidator shardLimitValidator = new ShardLimitValidator(Settings.EMPTY, clusterService);
             createIndexService = new MetadataCreateIndexService(
                 Settings.EMPTY,

modules/ingest-geoip/src/test/java/org/elasticsearch/ingest/geoip/DatabaseNodeServiceTests.java

@@ -383,7 +383,8 @@ static ClusterState createClusterState(PersistentTasksCustomMetadata tasksCustom
             new ShardId(index, 0),
             true,
             RecoverySource.ExistingStoreRecoverySource.INSTANCE,
-            new UnassignedInfo(UnassignedInfo.Reason.INDEX_CREATED, "")
+            new UnassignedInfo(UnassignedInfo.Reason.INDEX_CREATED, ""),
+            ShardRouting.Role.DEFAULT
         );
         String nodeId = ESTestCase.randomAlphaOfLength(8);
         shardRouting = shardRouting.initialize(nodeId, null, shardRouting.getExpectedShardSize());

server/src/internalClusterTest/java/org/elasticsearch/cluster/coordination/RareClusterStateIT.java

@@ -20,6 +20,7 @@
 import org.elasticsearch.action.support.master.AcknowledgedResponse;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.ClusterStateUpdateTask;
+import org.elasticsearch.cluster.TestShardRoutingRoleStrategies;
 import org.elasticsearch.cluster.block.ClusterBlocks;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.cluster.metadata.MappingMetadata;
@@ -102,7 +103,10 @@ public ClusterState execute(ClusterState currentState) {
                 builder.blocks(ClusterBlocks.builder().blocks(currentState.blocks()).removeIndexBlocks(index));
                 ClusterState updatedState = builder.build();
 
-                RoutingTable.Builder routingTable = RoutingTable.builder(updatedState.routingTable());
+                RoutingTable.Builder routingTable = RoutingTable.builder(
+                    TestShardRoutingRoleStrategies.DEFAULT_ROLE_ONLY,
+                    updatedState.routingTable()
+                );
                 routingTable.addAsRecovery(updatedState.metadata().index(index));
                 updatedState = ClusterState.builder(updatedState).routingTable(routingTable.build()).build();