Introduce allocation filter to control placement of search only replicas

Signed-off-by: Marc Handalian <[email protected]>

CHANGELOG.md

@@ -37,6 +37,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Adding translog durability validation in index templates ([#15494](https://github.com/opensearch-project/OpenSearch/pull/15494))
 - Add index creation using the context field ([#15290](https://github.com/opensearch-project/OpenSearch/pull/15290))
 - [Reader Writer Separation] Add searchOnly replica routing configuration ([#15410](https://github.com/opensearch-project/OpenSearch/pull/15410))
+- [Reader Writer Separation] Add allocation filter for search replicas ([#15455](https://github.com/opensearch-project/OpenSearch/pull/15455))
 
 ### Dependencies
 - Bump `netty` from 4.1.111.Final to 4.1.112.Final ([#15081](https://github.com/opensearch-project/OpenSearch/pull/15081))

server/src/internalClusterTest/java/org/opensearch/cluster/allocation/SearchReplicaFilteringAllocationIT.java

@@ -0,0 +1,125 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.cluster.allocation;
+
+import org.opensearch.cluster.metadata.IndexMetadata;
+import org.opensearch.cluster.routing.IndexShardRoutingTable;
+import org.opensearch.cluster.routing.ShardRouting;
+import org.opensearch.common.settings.Settings;
+import org.opensearch.common.util.FeatureFlags;
+import org.opensearch.indices.replication.common.ReplicationType;
+import org.opensearch.test.OpenSearchIntegTestCase;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+import static org.opensearch.cluster.metadata.IndexMetadata.SETTING_REPLICATION_TYPE;
+import static org.opensearch.cluster.routing.allocation.decider.FilterAllocationDecider.SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_SETTING;
+
+@OpenSearchIntegTestCase.ClusterScope(scope = OpenSearchIntegTestCase.Scope.TEST, numDataNodes = 0)
+public class SearchReplicaFilteringAllocationIT extends OpenSearchIntegTestCase {
+
+    @Override
+    protected Settings featureFlagSettings() {
+        return Settings.builder().put(super.featureFlagSettings()).put(FeatureFlags.READER_WRITER_SPLIT_EXPERIMENTAL, Boolean.TRUE).build();
+    }
+
+    public void testSearchReplicaDedicatedIncludes() {
+        List<String> nodesIds = internalCluster().startNodes(3);
+        final String node_0 = nodesIds.get(0);
+        final String node_1 = nodesIds.get(1);
+        final String node_2 = nodesIds.get(2);
+        assertEquals(3, cluster().size());
+
+        client().admin()
+            .cluster()
+            .prepareUpdateSettings()
+            .setTransientSettings(
+                Settings.builder().put(SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_SETTING.getKey() + "_name", node_1 + "," + node_0)
+            )
+            .execute()
+            .actionGet();
+
+        createIndex(
+            "test",
+            Settings.builder()
+                .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
+                .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0)
+                .put(IndexMetadata.SETTING_NUMBER_OF_SEARCH_REPLICAS, 1)
+                .put(SETTING_REPLICATION_TYPE, ReplicationType.SEGMENT)
+                .build()
+        );
+        ensureGreen("test");
+        // ensure primary is not on 1 or 2,
+        IndexShardRoutingTable routingTable = getRoutingTable();
+        assertEquals(node_2, getNodeName(routingTable.primaryShard().currentNodeId()));
+
+        String existingSearchReplicaNode = getNodeName(routingTable.searchOnlyReplicas().get(0).currentNodeId());
+        String emptyAllowedNode = existingSearchReplicaNode.equals(node_0) ? node_1 : node_0;
+
+        // set the included nodes to the other open node.
+        client().admin()
+            .cluster()
+            .prepareUpdateSettings()
+            .setTransientSettings(Settings.builder().put(SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_SETTING.getKey() + "_name", emptyAllowedNode))
+            .execute()
+            .actionGet();
+        ensureGreen("test");
+
+        routingTable = getRoutingTable();
+        assertEquals(node_2, getNodeName(routingTable.primaryShard().currentNodeId()));
+        assertEquals(emptyAllowedNode, getNodeName(routingTable.searchOnlyReplicas().get(0).currentNodeId()));
+    }
+
+    public void testSearchReplicaDedicatedIncludes_DoNotAssignToOtherNodes() {
+        List<String> nodesIds = internalCluster().startNodes(3);
+        final String node_0 = nodesIds.get(0);
+        final String node_1 = nodesIds.get(1);
+        final String node_2 = nodesIds.get(2);
+        assertEquals(3, cluster().size());
+
+        // set filter on 1 node and set search replica count to 2 - should leave 1 unassigned
+        client().admin()
+            .cluster()
+            .prepareUpdateSettings()
+            .setTransientSettings(Settings.builder().put(SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_SETTING.getKey() + "_name", node_1))
+            .execute()
+            .actionGet();
+
+        logger.info("--> creating an index with no replicas");
+        createIndex(
+            "test",
+            Settings.builder()
+                .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
+                .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0)
+                .put(IndexMetadata.SETTING_NUMBER_OF_SEARCH_REPLICAS, 2)
+                .put(SETTING_REPLICATION_TYPE, ReplicationType.SEGMENT)
+                .build()
+        );
+        ensureYellowAndNoInitializingShards("test");
+        IndexShardRoutingTable routingTable = getRoutingTable();
+        assertEquals(2, routingTable.searchOnlyReplicas().size());
+        List<ShardRouting> assignedSearchShards = routingTable.searchOnlyReplicas()
+            .stream()
+            .filter(ShardRouting::assignedToNode)
+            .collect(Collectors.toList());
+        assertEquals(1, assignedSearchShards.size());
+        assertEquals(node_1, getNodeName(assignedSearchShards.get(0).currentNodeId()));
+        assertEquals(1, routingTable.searchOnlyReplicas().stream().filter(ShardRouting::unassigned).count());
+    }
+
+    private IndexShardRoutingTable getRoutingTable() {
+        IndexShardRoutingTable routingTable = getClusterState().routingTable().index("test").getShards().get(0);
+        return routingTable;
+    }
+
+    private String getNodeName(String id) {
+        return getClusterState().nodes().get(id).getName();
+    }
+}

server/src/internalClusterTest/java/org/opensearch/indices/settings/SearchOnlyReplicaFeatureFlagIT.java

@@ -17,6 +17,7 @@
 
 import static org.opensearch.cluster.metadata.IndexMetadata.SETTING_NUMBER_OF_SEARCH_REPLICAS;
 import static org.opensearch.cluster.metadata.IndexMetadata.SETTING_REPLICATION_TYPE;
+import static org.opensearch.cluster.routing.allocation.decider.FilterAllocationDecider.SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_SETTING;
 
 @OpenSearchIntegTestCase.ClusterScope(scope = OpenSearchIntegTestCase.Scope.SUITE, numDataNodes = 1)
 public class SearchOnlyReplicaFeatureFlagIT extends OpenSearchIntegTestCase {
@@ -53,4 +54,15 @@ public void testUpdateFeatureFlagDisabled() {
         });
         assertTrue(settingsException.getMessage().contains("unknown setting"));
     }
+
+    public void testFilterAllocationSettingNotRegistered() {
+        expectThrows(SettingsException.class, () -> {
+            client().admin()
+                .cluster()
+                .prepareUpdateSettings()
+                .setTransientSettings(Settings.builder().put(SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_SETTING.getKey() + "_name", "node"))
+                .execute()
+                .actionGet();
+        });
+    }
 }

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

@@ -44,6 +44,7 @@
 import org.opensearch.common.settings.Setting;
 import org.opensearch.common.settings.Setting.Property;
 import org.opensearch.common.settings.Settings;
+import org.opensearch.common.util.FeatureFlags;
 import org.opensearch.node.remotestore.RemoteStoreNodeService;
 
 import java.util.Map;
@@ -88,6 +89,8 @@ public class FilterAllocationDecider extends AllocationDecider {
     private static final String CLUSTER_ROUTING_REQUIRE_GROUP_PREFIX = "cluster.routing.allocation.require";
     private static final String CLUSTER_ROUTING_INCLUDE_GROUP_PREFIX = "cluster.routing.allocation.include";
     private static final String CLUSTER_ROUTING_EXCLUDE_GROUP_PREFIX = "cluster.routing.allocation.exclude";
+    private static final String SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_PREFIX = "cluster.routing.allocation.search.replica.dedicated.include";
+
     public static final Setting.AffixSetting<String> CLUSTER_ROUTING_REQUIRE_GROUP_SETTING = Setting.prefixKeySetting(
         CLUSTER_ROUTING_REQUIRE_GROUP_PREFIX + ".",
         key -> Setting.simpleString(key, value -> IP_VALIDATOR.accept(key, value), Property.Dynamic, Property.NodeScope)
@@ -100,7 +103,12 @@ public class FilterAllocationDecider extends AllocationDecider {
         CLUSTER_ROUTING_EXCLUDE_GROUP_PREFIX + ".",
         key -> Setting.simpleString(key, value -> IP_VALIDATOR.accept(key, value), Property.Dynamic, Property.NodeScope)
     );
+    public static final Setting.AffixSetting<String> SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_SETTING = Setting.prefixKeySetting(
+        SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_PREFIX + ".",
+        key -> Setting.simpleString(key, value -> IP_VALIDATOR.accept(key, value), Property.Dynamic, Property.NodeScope)
+    );
 
+    private volatile DiscoveryNodeFilters searchReplicaIncludeFilters;
     private volatile DiscoveryNodeFilters clusterRequireFilters;
     private volatile DiscoveryNodeFilters clusterIncludeFilters;
     private volatile DiscoveryNodeFilters clusterExcludeFilters;
@@ -113,7 +121,6 @@ public FilterAllocationDecider(Settings settings, ClusterSettings clusterSetting
         setClusterIncludeFilters(CLUSTER_ROUTING_INCLUDE_GROUP_SETTING.getAsMap(settings));
         this.migrationDirection = RemoteStoreNodeService.MIGRATION_DIRECTION_SETTING.get(settings);
         this.compatibilityMode = RemoteStoreNodeService.REMOTE_STORE_COMPATIBILITY_MODE_SETTING.get(settings);
-
         clusterSettings.addAffixMapUpdateConsumer(CLUSTER_ROUTING_REQUIRE_GROUP_SETTING, this::setClusterRequireFilters, (a, b) -> {});
         clusterSettings.addAffixMapUpdateConsumer(CLUSTER_ROUTING_EXCLUDE_GROUP_SETTING, this::setClusterExcludeFilters, (a, b) -> {});
         clusterSettings.addAffixMapUpdateConsumer(CLUSTER_ROUTING_INCLUDE_GROUP_SETTING, this::setClusterIncludeFilters, (a, b) -> {});
@@ -122,6 +129,15 @@ public FilterAllocationDecider(Settings settings, ClusterSettings clusterSetting
             RemoteStoreNodeService.REMOTE_STORE_COMPATIBILITY_MODE_SETTING,
             this::setCompatibilityMode
         );
+
+        if (FeatureFlags.isEnabled(FeatureFlags.READER_WRITER_SPLIT_EXPERIMENTAL)) {
+            setSearchReplicaIncludeFilters(SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_SETTING.getAsMap(settings));
+            clusterSettings.addAffixMapUpdateConsumer(
+                SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_SETTING,
+                this::setSearchReplicaIncludeFilters,
+                (a, b) -> {}
+            );
+        }
     }
 
     private void setMigrationDirection(RemoteStoreNodeService.Direction migrationDirection) {
@@ -203,6 +219,9 @@ private Decision shouldFilter(ShardRouting shardRouting, DiscoveryNode node, Rou
         decision = shouldIndexFilter(allocation.metadata().getIndexSafe(shardRouting.index()), node, allocation);
         if (decision != null) return decision;
 
+        decision = shouldSearchReplicaShardTypeFilter(shardRouting, node, allocation);
+        if (decision != null) return decision;
+
         return allocation.decision(Decision.YES, NAME, "node passes include/exclude/require filters");
     }
 
@@ -294,6 +313,32 @@ private Decision shouldClusterFilter(DiscoveryNode node, RoutingAllocation alloc
         return null;
     }
 
+    private Decision shouldSearchReplicaShardTypeFilter(ShardRouting routing, DiscoveryNode node, RoutingAllocation allocation) {
+        if (searchReplicaIncludeFilters != null) {
+            final boolean match = searchReplicaIncludeFilters.match(node);
+            if (match == false && routing.isSearchOnly()) {
+                return allocation.decision(
+                    Decision.NO,
+                    NAME,
+                    "node does not match shard setting [%s] filters [%s]",
+                    SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_PREFIX,
+                    searchReplicaIncludeFilters
+                );
+            }
+            // filter will only apply to search replicas
+            if (routing.isSearchOnly() == false && match) {
+                return allocation.decision(
+                    Decision.NO,
+                    NAME,
+                    "only search replicas can be allocated to node with setting [%s] filters [%s]",
+                    SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_PREFIX,
+                    searchReplicaIncludeFilters
+                );
+            }
+        }
+        return null;
+    }
+
     private void setClusterRequireFilters(Map<String, String> filters) {
         clusterRequireFilters = DiscoveryNodeFilters.trimTier(
             DiscoveryNodeFilters.buildOrUpdateFromKeyValue(clusterRequireFilters, AND, filters)
@@ -311,4 +356,10 @@ private void setClusterExcludeFilters(Map<String, String> filters) {
             DiscoveryNodeFilters.buildOrUpdateFromKeyValue(clusterExcludeFilters, OR, filters)
         );
     }
+
+    private void setSearchReplicaIncludeFilters(Map<String, String> filters) {
+        searchReplicaIncludeFilters = DiscoveryNodeFilters.trimTier(
+            DiscoveryNodeFilters.buildOrUpdateFromKeyValue(searchReplicaIncludeFilters, OR, filters)
+        );
+    }
 }

server/src/main/java/org/opensearch/common/settings/ClusterSettings.java

@@ -805,6 +805,8 @@ public void apply(Settings value, Settings current, Settings previous) {
             OpenSearchOnHeapCacheSettings.EXPIRE_AFTER_ACCESS_SETTING.getConcreteSettingForNamespace(
                 CacheType.INDICES_REQUEST_CACHE.getSettingPrefix()
             )
-        )
+        ),
+        List.of(FeatureFlags.READER_WRITER_SPLIT_EXPERIMENTAL),
+        List.of(FilterAllocationDecider.SEARCH_REPLICA_ROUTING_INCLUDE_GROUP_SETTING)
     );
 }